UITextField中有一个placeholder属性,UITextField和UITe

作者: 编程  发布:2019-09-15

2、然后在相应的.m文件中,我们做如下操作:

1.创建textView

 #import "ViewController.h"#import <objc/runtime.h>#import <objc/message.h>@interface ViewController ()@end @implementation ViewController- viewDidLoad { [super viewDidLoad]; // 通过运行时,发现UITextView有一个叫做“_placeHolderLabel”的私有变量 unsigned int count = 0; Ivar *ivars = class_copyIvarList([UITextView class], &count); for (int i = 0; i < count; i++) { Ivar ivar = ivars[i]; const char *name = ivar_getName; NSString *objcName = [NSString stringWithUTF8String:name]; NSLog(@"%d : %@",i,objcName); } [self setupTextView]; } - setupTextView { UITextView *textView = [[UITextView alloc] initWithFrame:CGRectMake(0, 100, [UIScreen mainScreen].bounds.size.width, 100]; [textView setBackgroundColor:[UIColor greenColor]]; [self.view addSubview:textView]; // _placeholderLabel UILabel *placeHolderLabel = [[UILabel alloc] init]; placeHolderLabel.text = @"请输入内容"; placeHolderLabel.numberOfLines = 0; placeHolderLabel.textColor = [UIColor lightGrayColor]; [placeHolderLabel sizeToFit]; [textView addSubview:placeHolderLabel]; [textView setValue:placeHolderLabel forKey:@"_placeholderLabel"]; }@end

特点:该方法同样也可以实现类似于placeholder的功能。相比较方法一,方法二可以实现动态监听文本的改变,并非弹出键盘就立即清除placeholder,只有当用户开始输入文本的时候。placeholder才会消失。同样,当用户清空文本的时候,placeholder又会重新显示出来。

@interface YJPlaceholderTextView : UITextView@property (copy ,nonatomic) NSString *placeholder;@property (strong ,nonatomic) UIColor *placeholderColor;@end

 

前言iOS开发中,UITextField和UITextView是最常用的文本接受类和文本展示类的控件。UITextField和UITextView都输入文本,也都可以监听文本的改变。不同的是,UITextField继承自UIControl这个抽象类。UITextView继承自UIScrollView这个实体类。这就导致了UITextView可以多行展示内容,并且还可以像UIScrollView一样滚动。而UITextField只能单独的展示一行内容。从这个角度,UITextView在功能上是优于UITextField的。但是,众所周知,UITextField中有一个placeholder属性,可以设置UITextField的占位文字,起到提示用户输入相关信息的作用。可是,UITextView就没那么幸运了,apple没有给UITextView提供一个类似于placeholder这样的属性来供开发者使用。而开发中,我们经常会遇到既要占位文字,又要可以多行展示并且可以滚动的控件,单纯的UITextField或者UITextView都不能满足这种产品上的需求。比如,现在市面上的app大多都有一个用户反馈的入口,如下图所示。下面我就把自己能够想到的方法汇总一下,让更多的开发者知道,原来有这么多方法可以实现UITextView的占位文字。

#import <UIKit/UIKit.h>@interface WSPlaceholderTextView : UITextView/** 占位文字 */@property (nonatomic, copy) NSString *placeholder;/** 占位文字颜色 */@property (nonatomic, strong) UIColor *placeholderColor;@end#import "WSPlaceholderTextView.h"@implementation WSPlaceholderTextView- (instancetype)initWithFrame:frame{ if (self = [super initWithFrame:frame]) { // 设置默认字体 self.font = [UIFont systemFontOfSize:15]; // 设置默认颜色 self.placeholderColor = [UIColor grayColor]; // 使用通知监听文字改变 [[NSNotificationCenter defaultCenter] addObserver:self selector:@selector(textDidChange:) name:UITextViewTextDidChangeNotification object:self]; } return self;}- textDidChange:(NSNotification *)note{ // 会重新调用drawRect:方法 [self setNeedsDisplay];}- dealloc{ [[NSNotificationCenter defaultCenter] removeObserver:self];}/** * 每次调用drawRect:方法,都会将以前画的东西清除掉 */- drawRect:rect{ // 如果有文字,就直接返回,不需要画占位文字 if (self.hasText) return; // 属性 NSMutableDictionary *attrs = [NSMutableDictionary dictionary]; attrs[NSFontAttributeName] = self.font; attrs[NSForegroundColorAttributeName] = self.placeholderColor; // 画文字 rect.origin.x = 5; rect.origin.y = 8; rect.size.width -= 2 * rect.origin.x; [self.placeholder drawInRect:rect withAttributes:attrs];}- layoutSubviews{ [super layoutSubviews]; [self setNeedsDisplay];}#pragma mark - setter- setPlaceholder:(NSString *)placeholder{ _placeholder = [placeholder copy]; [self setNeedsDisplay];}- setPlaceholderColor:(UIColor *)placeholderColor{ _placeholderColor = placeholderColor; [self setNeedsDisplay];}- setFont:font{ [super setFont:font]; [self setNeedsDisplay];}- setText:(NSString *)text{ [super setText:text]; [self setNeedsDisplay];}- setAttributedText:(NSAttributedString *)attributedText{ [super setAttributedText:attributedText]; [self setNeedsDisplay];}@end

显然,上面的这些方法是我们对自定义的textView的属性进行的重写,这里重写一系列方法只是为了在系统通过代码修改这些属性的时候能够一样发生反应。并且、在这里我们用到了“setNeedsDisplay”这个方法,他并不是会立刻执行的一个方法,只有在下一个消息循环时候才会发生调用。

方法三:

同样地思路,我们也可以把作为占位文字的UILabel用UITextField或者UITextView来替换,同样可以实现带placeholder的textView,在次就不在详述。

#import "WSViewController.h"@interface WSViewController () <UITextViewDelegate>@property(nonatomic, weak)UITextView *textView;@property(nonatomic, weak)UILabel *placeHolder;@end@implementation WSViewController- viewDidLoad { [super viewDidLoad]; // Do any additional setup after loading the view. [self setupTextView];}// 添加textView- setupTextView{ UITextView *textView = [[UITextView alloc] initWithFrame:CGRectMake(10, 74, SCREEN_WIDTH - 2 * 10, 200)]; textView.frame = CGRectMake(10, 74, SCREEN_WIDTH - 2 * 10, 200); [self.view addSubview:textView]; self.textView = textView; textView.contentInset = UIEdgeInsetsMake(-64, 0, 0, 0); textView.delegate = self; [self setupPlaceHolder]; //在弹出的键盘上面加一个view来放置退出键盘的Done按钮 UIToolbar * topView = [[UIToolbar alloc] initWithFrame:CGRectMake(0, 0, 320, 30)]; [topView setBarStyle:UIBarStyleDefault]; UIBarButtonItem * btnSpace = [[UIBarButtonItem alloc] initWithBarButtonSystemItem:UIBarButtonSystemItemFlexibleSpace target:self action:nil]; UIBarButtonItem * doneButton = [[UIBarButtonItem alloc] initWithTitle:@"完成" style:UIBarButtonItemStyleDone target:self action:@selector(dismissKeyBoard)]; NSArray * buttonsArray = [NSArray arrayWithObjects:btnSpace, doneButton, nil]; [topView setItems:buttonsArray]; [textView setInputAccessoryView:topView];}// 给textView添加一个UILabel子控件- setupPlaceHolder{ UILabel *placeHolder = [[UILabel alloc] initWithFrame:CGRectMake(15, -2, SCREEN_WIDTH - 2 * 15, 200)]; self.placeHolder = placeHolder; placeHolder.text = @"我是placeholder"; placeHolder.textColor = [UIColor lightGrayColor]; placeHolder.numberOfLines = 0; placeHolder.contentMode = UIViewContentModeTop; [self.textView addSubview:placeHolder];}#pragma mark - UITextViewDelegate- textViewDidChange:(UITextView *)textView{ if (!textView.text.length) { self.placeHolder.alpha = 1; } else { self.placeHolder.alpha = 0; }}//关闭键盘- dismissKeyBoard{ [self.textView resignFirstResponder];}@end
#import "YJPlaceholderTextView.h"#define YJNotificationCenter [NSNotificationCenter defaultCenter]@implementation YJPlaceholderTextView- initWithFrame:frame{ if (self = [super initWithFrame:frame]) { // 设置通知监听文字的改变 [YJNotificationCenter addObserver:self selector:@selector(textDidChange) name:UITextViewTextDidChangeNotification object:self]; } return self;}

4.添加通知监听文字改变

特点:这种方法的特点是,当用户点击了textView,placeholder占位文字就会立马消失,官方的placeholder是当系统监听到用户输入了文字后placeholder才会消失。

1.创建textView2.给textView添加一个UILabel子控件,作为placeholder3.在文本改变的代理方法里面显示/隐藏UILabel

- setPlaceholder:(NSString *)placeholder{ _placeholder = [placeholder copy]; [self setNeedsDisplay];}- setPlaceholderColor:(UIColor *)placeholderColor{ _placeholderColor = placeholderColor; [self setNeedsDisplay];}- setText:(NSString *)text{ [super setText:text]; [self setNeedsDisplay];}-setFont:font{ [super setFont:font]; [self setNeedsDisplay];}

UITextField中有一个placeholder属性,可以设置UITextField的占位文字,起到提示用户的作用。可是UITextView就没那么幸运了,apple没有给UITextView提供一个类似于placeholder这样的属性来供开发者使用。下面我就把自己能够想到的和网友提供的方法汇总一下,让更多的开发者知道,原来有这么多方法可以实现UITextView的占位文字。

#import "WSViewController.h"@interface WSViewController () <UITextViewDelegate>@property(nonatomic, weak)UITextView *textView;@property(nonatomic, weak)UILabel *placeHolder;@end@implementation WSViewController- viewDidLoad { [super viewDidLoad]; // Do any additional setup after loading the view. [self setupTextView];}// 添加textView- setupTextView{ UITextView *textView = [[UITextView alloc] initWithFrame:CGRectMake(10, 74, SCREEN_WIDTH - 2 * 10, 200)]; textView.frame = CGRectMake(10, 74, SCREEN_WIDTH - 2 * 10, 200); [self.view addSubview:textView]; self.textView = textView; textView.contentInset = UIEdgeInsetsMake(-64, 0, 0, 0); textView.delegate = self; [self setupPlaceHolder]; //在弹出的键盘上面加一个view来放置退出键盘的Done按钮 UIToolbar * topView = [[UIToolbar alloc] initWithFrame:CGRectMake(0, 0, 320, 30)]; [topView setBarStyle:UIBarStyleDefault]; UIBarButtonItem * btnSpace = [[UIBarButtonItem alloc] initWithBarButtonSystemItem:UIBarButtonSystemItemFlexibleSpace target:self action:nil]; UIBarButtonItem * doneButton = [[UIBarButtonItem alloc] initWithTitle:@"完成" style:UIBarButtonItemStyleDone target:self action:@selector(dismissKeyBoard)]; NSArray * buttonsArray = [NSArray arrayWithObjects:btnSpace, doneButton, nil]; [topView setItems:buttonsArray]; [textView setInputAccessoryView:topView]; }// 给textView添加一个UILabel子控件- setupPlaceHolder{ UILabel *placeHolder = [[UILabel alloc] initWithFrame:CGRectMake(15, -2, SCREEN_WIDTH - 2 * 15, 200)]; self.placeHolder = placeHolder; placeHolder.text = @"我是placeholder"; placeHolder.textColor = [UIColor lightGrayColor]; placeHolder.numberOfLines = 0; placeHolder.contentMode = UIViewContentModeTop; [self.textView addSubview:placeHolder];}#pragma mark - UITextViewDelegate- textViewDidChange:(UITextView *)textView{ if (!textView.text.length) { self.placeHolder.alpha = 1; } else { self.placeHolder.alpha = 0; } }//关闭键盘- dismissKeyBoard{ [self.textView resignFirstResponder]; }@end

1.自定义UITextView2.给UITextView添加placeholder和placeholderColor属性3.重写initWithFrame方法4.添加通知监听文字改变5.重写drawRect:方法6.重写相关属性的set方法

最后,我们通过对“- drawRect:rect”方法的调用来实现placeholder的相关设置。

#import <UIKit/UIKit.h>

@interface WSTextView : UITextView
/** 占位文字 */
@property (nonatomic,copy) NSString *placeholder;
/** 占位文字颜色 */
@property (nonatomic,strong) UIColor *placeholderColor;
@end

#import "WSTextView.h"

@implementation WSTextView
- (instancetype)initWithFrame:(CGRect)frame
{
    if (self = [super initWithFrame:frame]) {
        self.font = [UIFont systemFontOfSize:15];
        self.placeholderColor = [UIColor lightGrayColor];
        self.placeholder = @"请输入内容";
    }
    return self;
}

// Only override drawRect: if you perform custom drawing.
// An empty implementation adversely affects performance during animation.
- (void)drawRect:(CGRect)rect {
    // Drawing code
    NSMutableDictionary *attrs = [NSMutableDictionary dictionary];
    attrs[NSFontAttributeName] = self.font;
    attrs[NSForegroundColorAttributeName] = self.placeholderColor;

    [self.placeholder drawInRect:CGRectMake(0, 0, self.frame.size.width, self.frame.size.height) withAttributes:attrs];
}

// 布局子控件的时候需要重绘
- (void)layoutSubviews
{
    [super layoutSubviews];
    [self setNeedsDisplay];

}
// 设置属性的时候需要重绘,所以需要重写相关属性的set方法
- (void)setPlaceholder:(NSString *)placeholder
{
    _placeholder = placeholder;
    [self setNeedsDisplay];
}

- (void)setPlaceholderColor:(UIColor *)placeholderColor
{
    _placeholderColor = placeholderColor;
    [self setNeedsDisplay];

}

- (void)setFont:(UIFont *)font
{
    [super setFont:font];
    [self setNeedsDisplay];
}

- (void)setText:(NSString *)text
{
    [super setText:text];
    if (text.length) { // 因为是在文本改变的代理方法中判断是否显示placeholder,而通过代码设置text的方式又不会调用文本改变的代理方法,所以再此根据text是否不为空判断是否显示placeholder。
        self.placeholder = @"";
    }
    [self setNeedsDisplay];
}

- (void)setAttributedText:(NSAttributedString *)attributedText
{
    [super setAttributedText:attributedText];
    if (attributedText.length) {
        self.placeholder = @"";
    }
    [self setNeedsDisplay];
}
@end

// 应用的时候需要配合UITextView的文本改变的代理方法

#import "ViewController.h"
#import "WSTextView.h"

@interface ViewController ()<UITextViewDelegate>

// @property(nonatomic,weak) WSTextView *textView;

@end

@implementation ViewController

- (void)viewDidLoad {
    [super viewDidLoad];
    // Do any additional setup after loading the view, typically from a nib.
}

- (void)didReceiveMemoryWarning {
    [super didReceiveMemoryWarning];
    // Dispose of any resources that can be recreated.
}

- (void)touchesBegan:(NSSet<UITouch *> *)touches withEvent:(UIEvent *)event
{
    WSTextView *textView = [[WSTextView alloc] initWithFrame:CGRectMake(10, 20, self.view.frame.size.width, 30)];
    textView.placeholder = @"ws";
    textView.delegate = self;
    [self.view addSubview:textView];
    // textView.text = @"试试会不会调用文本改变的代理方法"; // 不会调用文本改变的代理方法
    textView.attributedText = [[NSAttributedString alloc] initWithString:@"富文本"];

    // self.textView = textView;
}

#pragma mark - UITextViewDelegate
- (void)textViewDidChange:(WSTextView *)textView // 此处取巧,把代理方法参数类型直接改成自定义的WSTextView类型,为了可以使用自定义的placeholder属性,省去了通过给控制器WSTextView类型属性这样一步。
{
    if (textView.hasText) { // textView.text.length
        textView.placeholder = @"";

    } else {
        textView.placeholder = @"ws";

    }
}
@end

方法四1.自定义UITextView2.给UITextView添加placeholder和placeholderColor属性3.重写initWithFrame方法4.重写drawRect:方法5.重写相关属性的set方法

1.自定义UITextView2.给UITextView添加placeholder和placeholderColor属性3.重写initWithFrame方法4.重写drawRect:方法5.重写相关属性的set方法

在UI控件中,经常会用到UITextField和UITextView,但是我们都知道对于UITextView而言,它本身是没有占位文字placeholder这一属性的,那么,本文就将介绍如何编写一个带有占位文字的TextView。

5.重写相关属性的set方法

方法三1.自定义UITextView2.给UITextView添加placeholder和placeholderColor属性3.重写initWithFrame方法4.添加通知监听文字改变5.重写drawRect:方法6.重写相关属性的set方法

iOS开发中,UITextField和UITextView是最常用的文本接受类和文本展示类的控件。UITextField和UITextView都输入文本,也都可以监听文本的改变。不同的是,UITextField继承自UIControl这个抽象类。UITextView继承自UIScrollView这个实体类。这就导致了UITextView可以多行展示内容,并且还可以像UIScrollView一样滚动。而UITextField只能单独的展示一行内容。从这个角度,UITextView在功能上是优于UITextField的。但是,众所周知,UITextField中有一个placeholder属性,可以设置UITextField的占位文字,起到提示用户输入相关信息的作用。可是,UITextView就没那么幸运了,apple没有给UITextView提供一个类似于placeholder这样的属性来供开发者使用。而开发中,我们经常会遇到既要占位文字,又要可以多行展示并且可以滚动的控件,单纯的UITextField或者UITextView都不能满足这种产品上的需求。比如,现在市面上的app大多都有一个用户反馈的入口,如下图所示。下面我就把自己能够想到的方法汇总一下,让更多的开发者知道,原来有这么多方法可以实现UITextView的占位文字。

// 画占位文字- drawRect:rect{ if (self.hasText) return; CGFloat x = 5; CGFloat w = rect.size.width - 2*x; CGFloat y = 8; CGFloat h = rect.size.height - 2*y; CGRect placeholderRect = CGRectMake(x, y, w, h); NSMutableDictionary *attr = [NSMutableDictionary dictionary]; attr[NSFontAttributeName] = self.font; // 在没有设置字体颜色时默认为灰色 attr[NSForegroundColorAttributeName] = self.placeholderColor?self.placeholderColor:[UIColor grayColor]; // 画占位文字 [self.placeholder drawInRect:placeholderRect withAttributes:attr]; }

1.自定义UITextView

// 创建textViewUITextView *textView = [[UITextViewalloc]initWithFrame:CGRectMake(20,70,SCREEN.width-40,100)];textView.backgroundColor= [UIColor whiteColor];textView.text = @"我是placeholder";textView.textColor = [UIColor grayColor];textView.delegate = self;[self.view addSubview:textView];#pragma mark - UITextViewDelegate- textViewDidEndEditing:(UITextView *)textView{ if(textView.text.length < 1){ textView.text = @"我是placeholder"; textView.textColor = [UIColor grayColor]; } } - textViewDidBeginEditing:(UITextView *)textView{ if([textView.text isEqualToString:@"我是placeholder"]){ textView.text=@""; textView.textColor=[UIColor blackColor]; } }
// 创建textViewUITextView *textView =[[UITextViewalloc]initWithFrame:CGRectMake(20,70,SCREEN.width-40,100)];textView.backgroundColor= [UIColor whiteColor];textView.text = @"我是placeholder";textView.textColor = [UIColor grayColor];textView.delegate = self;[self.view addSubview:textView];#pragma mark - UITextViewDelegate- textViewDidEndEditing:(UITextView *)textView{ if(textView.text.length < 1){ textView.text = @"我是placeholder"; textView.textColor = [UIColor grayColor]; }}- textViewDidBeginEditing:(UITextView *)textView{ if([textView.text isEqualToString:@"我是placeholder"]){ textView.text=@""; textView.textColor=[UIColor blackColor]; }}
// 通知事件的响应方法- textDidChange{ // 重绘drawRect [self setNeedsDisplay];}

1.把UITextView的text属性当成“placeholder”使用。

特点:这个方法的和方法三很相似,只是没有利用通知来监听文本的改变,需要配合textViewDidChanged:这个文本改变的代理方法使用。

特点:这种方法的特点是,当用户点击了textView,placeholder占位文字就会立马消失,官方的placeholder是当系统监听到用户输入了文字后placeholder才会消失。

在这里,我定义了一个通知类的宏,用来简便书写通知事件。然后,我们开始书写TextView:

2.在开始编辑的代理方法里清除“placeholder”。

特点:相比计较上面两种方法,这种方法可移植性、拓展性更好,这种方法,不仅乐意随意通过我们添加的placeholder属性设置默认文字,还可以通过我们添加的placeholderColor设置默认文字的颜色。今后,我们只需要写好这么一个自定义UITextView,就可以一劳永逸。

通过runtime,我们发现,UITextView内部有一个名为“_placeHolderLabel”的私有成员变量。大家知道,Objective-C没有绝对的私有变量,因为我们可以通过KVC来访问私有变量。

到此,我们的自定义含有placeholder的UITextView就写好了。

2.给textView添加一个UILabel子控件,作为placeholder

方法五通过runtime,我们发现,UITextView内部有一个名为“_placeHolderLabel”的私有成员变量。大家知道,Objective-C没有绝对的私有变量,因为我们可以通过KVC来访问私有变量。

文/VV木公子PS:如非特别说明,所有文章均为原创作品,著作权归作者所有,转载转载请联系作者获得授权,并注明出处,所有打赏均归本人所有!

希望我的文章能对大家有所帮助。康撒米哒~~~

3.重写initWithFrame方法

 #import <UIKit/UIKit.h> @interface WSTextView : UITextView /** 占位文字 */ @property (nonatomic,copy) NSString *placeholder;/** 占位文字颜色 */@property (nonatomic,strong) UIColor *placeholderColor;@end#import "WSTextView.h"@implementation WSTextView - (instancetype)initWithFrame:frame{ if (self = [super initWithFrame:frame]) { self.font = [UIFont systemFontOfSize:15]; self.placeholderColor = [UIColor lightGrayColor]; self.placeholder = @"请输入内容"; } return self;}// Only override drawRect: if you perform custom drawing.// An empty implementation adversely affects performance during animation.- drawRect:rect { // Drawing code NSMutableDictionary *attrs = [NSMutableDictionary dictionary]; attrs[NSFontAttributeName] = self.font; attrs[NSForegroundColorAttributeName] = self.placeholderColor; [self.placeholder drawInRect:CGRectMake(0, 0, self.frame.size.width, self.frame.size.height) withAttributes:attrs];}// 布局子控件的时候需要重绘 - layoutSubviews { [super layoutSubviews]; [self setNeedsDisplay];}// 设置属性的时候需要重绘,所以需要重写相关属性的set方法- setPlaceholder:(NSString *)placeholder { _placeholder = placeholder; [self setNeedsDisplay];} - setPlaceholderColor:(UIColor *)placeholderColor{ _placeholderColor = placeholderColor; [self setNeedsDisplay];} - setFont:font{ [super setFont:font]; [self setNeedsDisplay]; } - setText:(NSString *)text{ [super setText:text]; if (text.length) { // 因为是在文本改变的代理方法中判断是否显示placeholder,而通 过代码设置text的方式又不会调用文本改变的代理方法,所以再此根据text是否不为空判 断是否显示placeholder。 self.placeholder = @""; } [self setNeedsDisplay];} - setAttributedText:(NSAttributedString *)attributedText{ [super setAttributedText:attributedText]; if (attributedText.length) { self.placeholder = @""; } [self setNeedsDisplay];}@end // 应用的时候需要配合UITextView的文本改变的代理方法#import "ViewController.h" #import "WSTextView.h"@interface ViewController ()<UITextViewDelegate>// @property(nonatomic,weak) WSTextView *textView;@end@implementation ViewController- viewDidLoad { [super viewDidLoad]; // Do any additional setup after loading the view, typically from a nib.}- didReceiveMemoryWarning { [super didReceiveMemoryWarning]; // Dispose of any resources that can be recreated.}- touchesBegan:(NSSet<UITouch *> *)touches withEvent:(UIEvent *)event{ WSTextView *textView = [[WSTextView alloc] initWithFrame:CGRectMake(10, 20, self.view.frame.size.width, 30)]; textView.placeholder = @"ws"; textView.delegate = self; [self.view addSubview:textView]; // textView.text = @"试试会不会调用文本改变的代理方法"; // 不会调用文本改变的代理方法 textView.attributedText = [[NSAttributedString alloc] initWithString:@"富文本"]; // self.textView = textView;}#pragma mark - UITextViewDelegate- textViewDidChange:(WSTextView *)textView // 此处取巧,把代理方法参数类型直接改成自定义的WSTextView类型,为了可以使用自定义的placeholder属性,省去了通过给控制器WSTextView类型属性这样一步。{ if (textView.hasText) { // textView.text.length textView.placeholder = @""; } else { textView.placeholder = @"ws"; }}@end

特点:9159.com ,这个方法的和方法三很相似,只是没有利用通知来监听文本的改变,需要配合textViewDidChanged:这个文本改变的代理方法使用。

1、首先自定义一个基于UITextView的YJPlaceholderTextView,.h文件中内容如下:

3.在文本改变的代理方法里面显示/隐藏UILabel

方法二1.创建textView2.给textView添加一个UILabel子控件,作为placeholder3.在文本改变的代理方法里面显示/隐藏UILabel

9159.com 1

通过runtime,我们发现,UITextView内部有一个名为“_placeHolderLabel”的私有成员变量。大家知道,Objective-C没有绝对的私有变量,因为我们可以通过KVC来访问私有变量。

特点:该方法同样也可以实现类似于placeholder的功能。相比较方法一,方法二可以实现动态监听文本的改变,并非弹出键盘就立即清除placeholder,只有当用户开始输入文本的时候。placeholder才会消失。同样,当用户清空文本的时候,placeholder又会重新显示出来。

特点:相对于上面的4种方法,这种方法更加取巧,虽然Apple官方没有给我们开发者提供类似于placeholder的属性,但是通过运行时,我们遍历出了一个placeHolderLabel的私有变量。这种方法简单易懂,代码量少,推荐大家使用这种方法。

 

方法一1.把UITextView的text属性当成“placeholder”使用。2.在开始编辑的代理方法里清除“placeholder”。3.在结束编辑的代理方法里根据条件设置“placeholder”。

特点:相比计较上面两种方法,这种方法可移植性、拓展性更好,这种方法,不仅乐意随意通过我们添加的placeholder属性设置默认文字,还可以通过我们添加的placeholderColor设置默认文字的颜色。今后,我们只需要写好这么一个自定义UITextView,就可以一劳永逸。

方法二:

 #import <UIKit/UIKit.h>@interface WSPlaceholderTextView : UITextView/** 占位文字 */@property (nonatomic, copy) NSString *placeholder;/** 占位文字颜色 */@property (nonatomic, strong) UIColor *placeholderColor;@end #import "WSPlaceholderTextView.h"@implementation WSPlaceholderTextView- (instancetype)initWithFrame:frame { if (self = [super initWithFrame:frame]) { // 设置默认字体 self.font = [UIFont systemFontOfSize:15]; // 设置默认颜色 self.placeholderColor = [UIColor grayColor]; // 使用通知监听文字改变 [[NSNotificationCenter defaultCenter] addObserver:self selector:@selector(textDidChange:) name:UITextViewTextDidChangeNotification object:self]; } return self;} - textDidChange:(NSNotification *)note{ // 会重新调用drawRect:方法 [self setNeedsDisplay];}- dealloc { [[NSNotificationCenter defaultCenter] removeObserver:self];} /** * 每次调用drawRect:方法,都会将以前画的东西清除掉 */ - drawRect:rect { // 如果有文字,就直接返回,不需要画占位文字 if (self.hasText) return; // 属性 NSMutableDictionary *attrs = [NSMutableDictionary dictionary]; attrs[NSFontAttributeName] = self.font; attrs[NSForegroundColorAttributeName] = self.placeholderColor; // 画文字 rect.origin.x = 5; rect.origin.y = 8; rect.size.width -= 2 * rect.origin.x; [self.placeholder drawInRect:rect withAttributes:attrs]; } - layoutSubviews{ [super layoutSubviews]; [self setNeedsDisplay];}#pragma mark - setter- setPlaceholder:(NSString *)placeholder{ _placeholder = [placeholder copy]; [self setNeedsDisplay];}- setPlaceholderColor:(UIColor *)placeholderColor{ _placeholderColor = placeholderColor; [self setNeedsDisplay]; }- setFont:font{ [super setFont:font]; [self setNeedsDisplay];}- setText:(NSString *)text{ [super setText:text]; [self setNeedsDisplay];}- setAttributedText:(NSAttributedString *)attributedText{ [super setAttributedText:attributedText]; [self setNeedsDisplay];}@end
#import <UIKit/UIKit.h>@interface WSTextView : UITextView/** 占位文字 */@property (nonatomic,copy) NSString *placeholder;/** 占位文字颜色 */@property (nonatomic,strong) UIColor *placeholderColor;@end#import "WSTextView.h"@implementation WSTextView- (instancetype)initWithFrame:frame{ if (self = [super initWithFrame:frame]) { self.font = [UIFont systemFontOfSize:15]; self.placeholderColor = [UIColor lightGrayColor]; self.placeholder = @"请输入内容"; } return self;}// Only override drawRect: if you perform custom drawing.// An empty implementation adversely affects performance during animation.- drawRect:rect { // Drawing code NSMutableDictionary *attrs = [NSMutableDictionary dictionary]; attrs[NSFontAttributeName] = self.font; attrs[NSForegroundColorAttributeName] = self.placeholderColor; [self.placeholder drawInRect:CGRectMake(0, 0, self.frame.size.width, self.frame.size.height) withAttributes:attrs];}// 布局子控件的时候需要重绘- layoutSubviews{ [super layoutSubviews]; [self setNeedsDisplay]; }// 设置属性的时候需要重绘,所以需要重写相关属性的set方法- setPlaceholder:(NSString *)placeholder{ _placeholder = placeholder; [self setNeedsDisplay];}- setPlaceholderColor:(UIColor *)placeholderColor{ _placeholderColor = placeholderColor; [self setNeedsDisplay]; }- setFont:font{ [super setFont:font]; [self setNeedsDisplay];}- setText:(NSString *)text{ [super setText:text]; if (text.length) { // 因为是在文本改变的代理方法中判断是否显示placeholder,而通过代码设置text的方式又不会调用文本改变的代理方法,所以再此根据text是否不为空判断是否显示placeholder。 self.placeholder = @""; } [self setNeedsDisplay];}- setAttributedText:(NSAttributedString *)attributedText{ [super setAttributedText:attributedText]; if (attributedText.length) { self.placeholder = @""; } [self setNeedsDisplay];}@end// 应用的时候需要配合UITextView的文本改变的代理方法#import "ViewController.h"#import "WSTextView.h"@interface ViewController ()<UITextViewDelegate>// @property(nonatomic,weak) WSTextView *textView;@end@implementation ViewController- viewDidLoad { [super viewDidLoad]; // Do any additional setup after loading the view, typically from a nib.}- didReceiveMemoryWarning { [super didReceiveMemoryWarning]; // Dispose of any resources that can be recreated.}- touchesBegan:(NSSet<UITouch *> *)touches withEvent:(UIEvent *)event{ WSTextView *textView = [[WSTextView alloc] initWithFrame:CGRectMake(10, 20, self.view.frame.size.width, 30)]; textView.placeholder = @"ws"; textView.delegate = self; [self.view addSubview:textView]; // textView.text = @"试试会不会调用文本改变的代理方法"; // 不会调用文本改变的代理方法 textView.attributedText = [[NSAttributedString alloc] initWithString:@"富文本"]; // self.textView = textView;}#pragma mark - UITextViewDelegate- textViewDidChange:(WSTextView *)textView // 此处取巧,把代理方法参数类型直接改成自定义的WSTextView类型,为了可以使用自定义的placeholder属性,省去了通过给控制器WSTextView类型属性这样一步。{ if (textView.hasText) { // textView.text.length textView.placeholder = @""; } else { textView.placeholder = @"ws"; }}@end
#import "WSViewController.h"

@interface WSViewController () <UITextViewDelegate>

@property(nonatomic, weak)UITextView *textView;

@property(nonatomic, weak)UILabel *placeHolder;

@end

@implementation WSViewController

- (void)viewDidLoad {
    [super viewDidLoad];
    // Do any additional setup after loading the view.

    [self setupTextView];

}

// 添加textView
- (void)setupTextView
{
    UITextView *textView = [[UITextView alloc] initWithFrame:CGRectMake(10, 74, SCREEN_WIDTH - 2 * 10, 200)];
    textView.frame = CGRectMake(10, 74, SCREEN_WIDTH - 2 * 10, 200);

    [self.view addSubview:textView];
    self.textView = textView;

    textView.contentInset = UIEdgeInsetsMake(-64, 0, 0, 0);

    textView.delegate = self;
    [self setupPlaceHolder];


    //在弹出的键盘上面加一个view来放置退出键盘的Done按钮
    UIToolbar * topView = [[UIToolbar alloc] initWithFrame:CGRectMake(0, 0, 320, 30)];
    [topView setBarStyle:UIBarStyleDefault];
    UIBarButtonItem * btnSpace = [[UIBarButtonItem alloc] initWithBarButtonSystemItem:UIBarButtonSystemItemFlexibleSpace target:self action:nil];
    UIBarButtonItem * doneButton = [[UIBarButtonItem alloc] initWithTitle:@"完成" style:UIBarButtonItemStyleDone target:self action:@selector(dismissKeyBoard)];
    NSArray * buttonsArray = [NSArray arrayWithObjects:btnSpace, doneButton, nil];

    [topView setItems:buttonsArray];
    [textView setInputAccessoryView:topView];

}

// 给textView添加一个UILabel子控件
- (void)setupPlaceHolder
{
    UILabel *placeHolder = [[UILabel alloc] initWithFrame:CGRectMake(15, -2, SCREEN_WIDTH - 2 * 15, 200)];
    self.placeHolder = placeHolder;

    placeHolder.text = @"我是placeholder";
    placeHolder.textColor = [UIColor lightGrayColor];
    placeHolder.numberOfLines = 0;
    placeHolder.contentMode = UIViewContentModeTop;
    [self.textView addSubview:placeHolder];
}

#pragma mark - UITextViewDelegate
- (void)textViewDidChange:(UITextView *)textView
{
    if (!textView.text.length) {
    self.placeHolder.alpha = 1;
    } else {
        self.placeHolder.alpha = 0;
    }
}

//关闭键盘
-(void) dismissKeyBoard{
    [self.textView resignFirstResponder];
}

@end

特点:相对于上面的4种方法,这种方法更加取巧,虽然Apple官方没有给我们开发者提供类似于placeholder的属性,但是通过运行时,我们遍历出了一个placeHolderLabel的私有变量。这种方法简单易懂,代码量少,推荐大家使用这种方法。

同样地思路,我们也可以把作为占位文字的UILabel用UITextField或者UITextView来替换,同样可以实现带placeholder的textView,在次就不在详述。

方法五:

1.把UITextView的text属性当成“placeholder”使用。2.在开始编辑的代理方法里清除“placeholder”。3.在结束编辑的代理方法里根据条件设置“placeholder”。

方法四: 

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1.自定义UITextView

#import "ViewController.h"#import <objc/runtime.h>#import <objc/message.h>@interface ViewController ()@end@implementation ViewController- viewDidLoad { [super viewDidLoad]; // 通过运行时,发现UITextView有一个叫做“_placeHolderLabel”的私有变量 unsigned int count = 0; Ivar *ivars = class_copyIvarList([UITextView class], &count); for (int i = 0; i < count; i++) { Ivar ivar = ivars[i]; const char *name = ivar_getName; NSString *objcName = [NSString stringWithUTF8String:name]; NSLog(@"%d : %@",i,objcName); } [self setupTextView]; }- setupTextView{ UITextView *textView = [[UITextView alloc] initWithFrame:CGRectMake(0, 100, [UIScreen mainScreen].bounds.size.width, 100]; [textView setBackgroundColor:[UIColor greenColor]]; [self.view addSubview:textView]; // _placeholderLabel UILabel *placeHolderLabel = [[UILabel alloc] init]; placeHolderLabel.text = @"请输入内容"; placeHolderLabel.numberOfLines = 0; placeHolderLabel.textColor = [UIColor lightGrayColor]; [placeHolderLabel sizeToFit]; [textView addSubview:placeHolderLabel]; // same font textView.font = [UIFont systemFontOfSize:13.f]; placeHolderLabel.font = [UIFont systemFontOfSize:13.f]; [textView setValue:placeHolderLabel forKey:@"_placeholderLabel"];}@end

特点:这个方法的和方法三很相似,只是没有利用通知来监听文本的改变,需要配合textViewDidChanged:这个文本改变的代理方法使用。

2.给UITextView添加placeholder和placeholderColor属性

5.重写drawRect:方法

特点:这种方法的特点是,当用户点击了textView,placeholder占位文字就会立马消失,官方的placeholder是当系统监听到用户输入了文字后placeholder才会消失。

2.给UITextView添加placeholder和placeholderColor属性

3.重写initWithFrame方法

 

同样地思路,我们也可以用两个UITextView来实现placeholder的功能,再次就不在详述。

方法一:

3.在结束编辑的代理方法里根据条件设置“placeholder”。

特点:相比计较上面两种方法,这种方法可移植性、拓展性更好,这种方法,不仅乐意随意通过我们添加的placeholder属性设置默认文字,还可以通过我们添加的placeholderColor设置默认文字的颜色。今后,我们只需要写好这么一个自定义UITextView,就可以一劳永逸。

// 创建textView
UITextView *textView =[[UITextViewalloc]initWithFrame:CGRectMake(20,70,SCREEN.width-40,100)];
textView.backgroundColor= [UIColor whiteColor];
textView.text = @"我是placeholder";
textView.textColor = [UIColor grayColor];
textView.delegate = self;
[self.view addSubview:textView];

#pragma mark - UITextViewDelegate
- (void)textViewDidEndEditing:(UITextView *)textView
{
    if(textView.text.length < 1){
        textView.text = @"我是placeholder";
        textView.textColor = [UIColor grayColor];
    }
}
- (void)textViewDidBeginEditing:(UITextView *)textView
{
    if([textView.text isEqualToString:@"我是placeholder"]){
        textView.text=@"";
        textView.textColor=[UIColor blackColor];
    }
}

4.重写drawRect:方法

特点:该方法同样也可以实现类似于placeholder的功能。相比较方法一,方法二可以实现动态监听文本的改变,并非弹出键盘就立即清除placeholder,只有当用户开始输入文本的时候。placeholder才会消失。同样,当用户清空文本的时候,placeholder又会重新显示出来。

#import "ViewController.h"
#import <objc/runtime.h>
#import <objc/message.h>

@interface ViewController ()

@end

@implementation ViewController

- (void)viewDidLoad {
    [super viewDidLoad];


  // 通过运行时,发现UITextView有一个叫做“_placeHolderLabel”的私有变量
    unsigned int count = 0;
    Ivar *ivars = class_copyIvarList([UITextView class], &count);

    for (int i = 0; i < count; i++) {
        Ivar ivar = ivars[i];
        const char *name = ivar_getName(ivar);
        NSString *objcName = [NSString stringWithUTF8String:name];
        NSLog(@"%d : %@",i,objcName);
    }

    [self setupTextView];

}
- (void)setupTextView
{
    UITextView *textView = [[UITextView alloc] initWithFrame:CGRectMake(0, 100, [UIScreen mainScreen].bounds.size.width, 100];
    [textView setBackgroundColor:[UIColor greenColor]];
    [self.view addSubview:textView];

    // _placeholderLabel
    UILabel *placeHolderLabel = [[UILabel alloc] init];
    placeHolderLabel.text = @"请输入内容";
    placeHolderLabel.numberOfLines = 0;
    placeHolderLabel.textColor = [UIColor lightGrayColor];
    [placeHolderLabel sizeToFit];
    [textView addSubview:placeHolderLabel];

    [textView setValue:placeHolderLabel forKey:@"_placeholderLabel"];

}

@end
#import <UIKit/UIKit.h>

@interface WSPlaceholderTextView : UITextView
/** 占位文字 */
@property (nonatomic, copy) NSString *placeholder;
/** 占位文字颜色 */
@property (nonatomic, strong) UIColor *placeholderColor;
@end

#import "WSPlaceholderTextView.h"

@implementation WSPlaceholderTextView

- (instancetype)initWithFrame:(CGRect)frame
{
    if (self = [super initWithFrame:frame]) {
        // 设置默认字体
        self.font = [UIFont systemFontOfSize:15];

        // 设置默认颜色
        self.placeholderColor = [UIColor grayColor];

        // 使用通知监听文字改变
        [[NSNotificationCenter defaultCenter] addObserver:self selector:@selector(textDidChange:) name:UITextViewTextDidChangeNotification object:self];
    }
    return self;
}

- (void)textDidChange:(NSNotification *)note
{
    // 会重新调用drawRect:方法
    [self setNeedsDisplay];
}

- (void)dealloc
{
    [[NSNotificationCenter defaultCenter] removeObserver:self];
}

/**
 * 每次调用drawRect:方法,都会将以前画的东西清除掉
 */
- (void)drawRect:(CGRect)rect
{
    // 如果有文字,就直接返回,不需要画占位文字
    if (self.hasText) return;

    // 属性
    NSMutableDictionary *attrs = [NSMutableDictionary dictionary];
    attrs[NSFontAttributeName] = self.font;
    attrs[NSForegroundColorAttributeName] = self.placeholderColor;

    // 画文字
    rect.origin.x = 5;
    rect.origin.y = 8;
    rect.size.width -= 2 * rect.origin.x;
    [self.placeholder drawInRect:rect withAttributes:attrs];
}

- (void)layoutSubviews
{
    [super layoutSubviews];

    [self setNeedsDisplay];
}

#pragma mark - setter
- (void)setPlaceholder:(NSString *)placeholder
{
    _placeholder = [placeholder copy];

    [self setNeedsDisplay];
}

- (void)setPlaceholderColor:(UIColor *)placeholderColor
{
    _placeholderColor = placeholderColor;

    [self setNeedsDisplay];
}

- (void)setFont:(UIFont *)font
{
    [super setFont:font];

    [self setNeedsDisplay];
}

- (void)setText:(NSString *)text
{
    [super setText:text];

    [self setNeedsDisplay];
}

- (void)setAttributedText:(NSAttributedString *)attributedText
{
    [super setAttributedText:attributedText];

    [self setNeedsDisplay];
}
@end

6.重写相关属性的set方法

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