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(,,SCREEN.width-,)];
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 < ){
        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(, , SCREEN_WIDTH -  * , )];
    textView.frame = CGRectMake(, , SCREEN_WIDTH -  * , );

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

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

    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(, , , )];
    [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(, -, SCREEN_WIDTH -  * , )];
    self.placeHolder = placeHolder;

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

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

//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:];

        // 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 = ;
    rect.origin.y = ;
    rect.size.width -=  * 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:];
        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(, , 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(, , self.view.frame.size.width, )];
    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 = ;
    Ivar *ivars = class_copyIvarList([UITextView class], &count);

    for (int i = ; 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(, , [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 = ;
    placeHolderLabel.textColor = [UIColor lightGrayColor];
    [placeHolderLabel sizeToFit];
    [textView addSubview:placeHolderLabel];

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

}

@end