UITextView实现placeHolder方法汇总
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。
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：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。
// 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]; } }
方法二：
1.创建textView
2.给textView添加一个UILabel子控件，作为placeholder
3.在文本改变的代理方法里面显示/隐藏UILabel
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。
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。
#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
方法三：
1.自定义UITextView
2.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
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。
#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
方法四：
1.自定义UITextView
2.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
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。
#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。
#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
