前言：在開(kāi)發(fā)過(guò)程當(dāng)中奕锌，我們很多時(shí)候會(huì)遇到在textView中像textFiled用到占位符的情況，也就是一個(gè)placeHold村生。但是系統(tǒng)并沒(méi)有給textView提供這個(gè)屬性惊暴，所以我們需要自己來(lái)實(shí)現(xiàn)。正好寫(xiě)項(xiàng)目遇到這種情況趁桃，就把我知道的幾種能實(shí)現(xiàn)的方式都實(shí)現(xiàn)了出來(lái)辽话。

• 第一種方式 簡(jiǎn)單粗暴

這種方法的特點(diǎn)是，當(dāng)用戶點(diǎn)擊了TextView的卫病，占位符占位文字就會(huì)立馬消失油啤，官方的占位符是當(dāng)系統(tǒng)監(jiān)聽(tīng)到用戶輸入了文字后占位符才會(huì)消失.

//    1.把UITextView的文本屬性當(dāng)成“placeholder”使用
//    2.在開(kāi)始編輯的代理方法里清除“placeholder”
//    3.在結(jié)束編輯的代理方法里根據(jù)條件設(shè)置“placeholder”。

 // 創(chuàng)建textView
    UITextView *textView =[[UITextView alloc]initWithFrame:CGRectMake(20,70,[UIScreen mainScreen].bounds.size.width-40,200)];
    textView.backgroundColor= [UIColor grayColor];
    textView.text = @"這種方法的特點(diǎn)是蟀苛，當(dāng)用戶點(diǎn)擊了TextView的益咬，占位符占位文字就會(huì)立馬消失，官方的占位符是當(dāng)系統(tǒng)監(jiān)聽(tīng)到用戶輸入了文字后占位符才會(huì)消失";
    textView.textColor = [UIColor lightGrayColor];
    textView.delegate = self;
    [self.view addSubview:textView];

代理方法：

#pragma mark - UITextViewDelegate
- (void)textViewDidEndEditing:(UITextView *)textView
{
    if(textView.text.length < 1){
        textView.text = @"這種方法的特點(diǎn)是帜平，當(dāng)用戶點(diǎn)擊了TextView的幽告，占位符占位文字就會(huì)立馬消失，官方的占位符是當(dāng)系統(tǒng)監(jiān)聽(tīng)到用戶輸入了文字后占位符才會(huì)消失";
        textView.textColor = [UIColor grayColor];
    }
}
- (void)textViewDidBeginEditing:(UITextView *)textView
{
    if([textView.text isEqualToString:@"這種方法的特點(diǎn)是裆甩，當(dāng)用戶點(diǎn)擊了TextView的冗锁，占位符占位文字就會(huì)立馬消失，官方的占位符是當(dāng)系統(tǒng)監(jiān)聽(tīng)到用戶輸入了文字后占位符才會(huì)消失"]){
        textView.text=@"";
        textView.textColor=[UIColor blackColor];
    }
}

• 第二種

該方法同樣也可以實(shí)現(xiàn)類(lèi)似于占位符的功能相比較方法一淑掌，方法二可以實(shí)現(xiàn)動(dòng)態(tài)監(jiān)聽(tīng)文本的改變蒿讥，并非彈出鍵盤(pán)就立即清除占位符，只有當(dāng)用戶開(kāi)始輸入文本的時(shí)候.placeholder才會(huì)消失抛腕。同樣芋绸，當(dāng)用戶清空文本的時(shí)候，占位符又會(huì)重新顯示出來(lái)担敌。

這種方法最致命的弊端在于要設(shè)置textView的偏移來(lái)設(shè)置label的位置摔敛，不好控制

//    1.創(chuàng)建textView
    UITextView *textView = [[UITextView alloc] initWithFrame:CGRectMake(10, 74, [UIScreen mainScreen].bounds.size.width - 20, 200)];
    textView.backgroundColor = [UIColor grayColor];
    
    [self.view addSubview:textView];
    self.textView = textView;
    self.textView.delegate = self;
    
    textView.contentInset = UIEdgeInsetsMake(-30, 0, 0, 0);

//    2.給textView添加一個(gè)UILabel子控件，作為占位符
    UILabel *placeHolder = [[UILabel alloc] initWithFrame:CGRectMake(15, 0, [UIScreen mainScreen].bounds.size.width - 50, 200)];
    self.placeHolder = placeHolder;
    placeHolder.text = @"該方法同樣也可以實(shí)現(xiàn)類(lèi)似于占位符的功能相比較方法一全封，方法二可以實(shí)現(xiàn)動(dòng)態(tài)監(jiān)聽(tīng)文本的改變马昙，并非彈出鍵盤(pán)就立即清除占位符，只有當(dāng)用戶開(kāi)始輸入文本的時(shí)候.placeholder才會(huì)消失刹悴。同樣行楞，當(dāng)用戶清空文本的時(shí)候，占位符又會(huì)重新顯示出來(lái)土匀。";
    placeHolder.textColor = [UIColor lightGrayColor];
    placeHolder.numberOfLines = 0;
    placeHolder.contentMode = UIViewContentModeTop;
    [self.textView addSubview:placeHolder];

代理方法

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

• 第三種

相比計(jì)較上面兩種方法子房，這種方法可移植性、拓展性更好，這種方法证杭，不僅樂(lè)意隨意通過(guò)我們添加的placeholder屬性設(shè)置默認(rèn)文字田度，還可以通過(guò)我們添加的placeholderColor設(shè)置默認(rèn)文字的顏色。今后解愤，我們只需要寫(xiě)好這么一個(gè)自定義UITextView镇饺，·就可以一勞永逸。

// 1.自定義UITextView（繼承UITextView）
// 2.給UITextView添加placeholder和placeholderColor屬性
// 3.重寫(xiě)initWithFrame方法
// 4.添加通知監(jiān)聽(tīng)文字改變
// 5.重寫(xiě)drawRect：方法
// 6.重寫(xiě)相關(guān)屬性的set方法

@interface SYJThirdTextView : UITextView
/** 占位文字 */
@property (nonatomic, copy) NSString *placeholder;
/** 占位文字顏色 */
@property (nonatomic, strong) UIColor *placeholderColor;
@end

#.m中實(shí)現(xiàn)

- (instancetype)initWithFrame:(CGRect)frame
{
    if (self = [super initWithFrame:frame]) {
        // 設(shè)置默認(rèn)字體
        self.font = [UIFont systemFontOfSize:15];
        // 設(shè)置默認(rèn)顏色
        self.placeholderColor = [UIColor grayColor];
        
        // 使用通知監(jiān)聽(tīng)文字改變
        [[NSNotificationCenter defaultCenter] addObserver:self selector:@selector(textDidChange:) name:UITextViewTextDidChangeNotification object:self];
    }
    return self;
}

- (void)textDidChange:(NSNotification *)note
{
    // 會(huì)重新調(diào)用drawRect:方法
    [self setNeedsDisplay];
}

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

/**
 * 每次調(diào)用drawRect:方法送讲，都會(huì)將以前畫(huà)的東西清除掉
 */
- (void)drawRect:(CGRect)rect
{
    // 如果有文字奸笤，就直接返回，不需要畫(huà)占位文字
    if (self.hasText) return;
    
    // 屬性
    NSMutableDictionary *attrs = [NSMutableDictionary dictionary];
    attrs[NSFontAttributeName] = self.font;
    attrs[NSForegroundColorAttributeName] = self.placeholderColor;
    
    // 畫(huà)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];
}

    SYJThirdTextView *textView = [[SYJThirdTextView alloc]init];
    [self.view addSubview:textView];
    textView.frame = CGRectMake(10, 100, [UIScreen mainScreen].bounds.size.width - 20, 240);
    textView.placeholder = @"相比計(jì)較上面兩種方法李茫，這種方法可移植性揭保、拓展性更好，這種方法魄宏，不僅樂(lè)意隨意通過(guò)我們添加的placeholder屬性設(shè)置默認(rèn)文字秸侣，還可以通過(guò)我們添加的placeholderColor設(shè)置默認(rèn)文字的顏色。今后宠互，我們只需要寫(xiě)好這么一個(gè)自定義UITextView味榛，就可以一勞永逸。";
    textView.backgroundColor = [UIColor grayColor];
    //占位符顏色
    textView.placeholderColor = [UIColor lightGrayColor];

• 第四種

這個(gè)方法的和方法三很相似予跌，只是沒(méi)有利用通知來(lái)監(jiān)聽(tīng)文本的改變搏色，需要配合textViewDidChanged:這個(gè)文本改變的代理方法使用。

@interface SYJFourTextView : UITextView

//1.自定義UITextView
//2.給UITextView添加placeholder和placeholderColor屬性
//3.重寫(xiě)initWithFrame方法
//4.重寫(xiě)drawRect：方法
//5.重寫(xiě)相關(guān)屬性的set方法

/** 占位文字 */
@property (nonatomic,copy) NSString *placeholder;
/** 占位文字顏色 */
@property (nonatomic,strong) UIColor *placeholderColor;

@end

- (instancetype)initWithFrame:(CGRect)frame
{
    if (self = [super initWithFrame:frame]) {
        self.font = [UIFont systemFontOfSize:15];
        self.placeholderColor = [UIColor lightGrayColor];
        self.placeholder = @"請(qǐng)輸入內(nèi)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];
}

// 布局子控件的時(shí)候需要重繪
- (void)layoutSubviews
{
    [super layoutSubviews];
    [self setNeedsDisplay];
    
}
// 設(shè)置屬性的時(shí)候需要重繪券册，所以需要重寫(xiě)相關(guān)屬性的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?yàn)槭窃谖谋靖淖兊拇矸椒ㄖ信袛嗍欠耧@示placeholder频轿，而通過(guò)代碼設(shè)置text的方式又不會(huì)調(diào)用文本改變的代理方法，所以再此根據(jù)text是否不為空判斷是否顯示placeholder烁焙。
        self.placeholder = @"";
    }
    [self setNeedsDisplay];
}

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

SYJFourTextView *textView = [[SYJFourTextView alloc] initWithFrame:CGRectMake(10, 80, self.view.frame.size.width - 20, 240)];
    textView.backgroundColor = [UIColor grayColor];
    textView.placeholder = @"這個(gè)方法的和方法三很相似航邢，只是沒(méi)有利用通知來(lái)監(jiān)聽(tīng)文本的改變，需要配合textViewDidChanged:這個(gè)文本改變的代理方法使用骄蝇。";
    textView.placeholderColor = [UIColor lightGrayColor];
    textView.delegate = self;
    [self.view addSubview:textView];

#pragma mark - UITextViewDelegate
- (void)textViewDidChange:(SYJFourTextView *)textView // 此處取巧膳殷，把代理方法參數(shù)類(lèi)型直接改成自定義的SYJFourTextView類(lèi)型，為了可以使用自定義的placeholder屬性九火，省去了通過(guò)給控制器SYJFourTextView類(lèi)型屬性這樣一步赚窃。
{
    if (textView.hasText) { // textView.text.length
        textView.placeholder = @"";
        
    } else {
        textView.placeholder = @"這個(gè)方法的和方法三很相似，只是沒(méi)有利用通知來(lái)監(jiān)聽(tīng)文本的改變岔激，需要配合textViewDidChanged:這個(gè)文本改變的代理方法使用";
        
    }
}

• 第五種 <推薦>

相對(duì)于上面的4種方法勒极，這種方法更加取巧，雖然Apple官方?jīng)]有給我們開(kāi)發(fā)者提供類(lèi)似于placeholder的屬性虑鼎，但是通過(guò)運(yùn)行時(shí)辱匿，我們遍歷出了一個(gè)placeHolderLabel的私有變量。這種方法簡(jiǎn)單易懂，代碼量少掀鹅，推薦大家使用這種方法。

//    通過(guò)runtime媒楼，我們發(fā)現(xiàn)乐尊，UITextView內(nèi)部有一個(gè)名為“_placeHolderLabel”的私有成員變量。大家知道划址，Objective-C沒(méi)有絕對(duì)的私有變量扔嵌，因?yàn)槲覀兛梢酝ㄟ^(guò)KVC來(lái)訪問(wèn)私有變量。

    UITextView *textView = [[UITextView alloc] initWithFrame:CGRectMake(10, 100, [UIScreen mainScreen].bounds.size.width -20, 240)];
    [textView setBackgroundColor:[UIColor greenColor]];
    [self.view addSubview:textView];
    
    // _placeholderLabel
    UILabel *placeHolderLabel = [[UILabel alloc] init];
    placeHolderLabel.text = @"相對(duì)于上面的4種方法夺颤，這種方法更加取巧痢缎，雖然Apple官方?jīng)]有給我們開(kāi)發(fā)者提供類(lèi)似于placeholder的屬性，但是通過(guò)運(yùn)行時(shí)世澜，我們遍歷出了一個(gè)placeHolderLabel的私有變量独旷。這種方法簡(jiǎn)單易懂，代碼量少寥裂，推薦大家使用這種方法嵌洼。";
    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"];
                

• 第六種（高大上）

這種方法就是比較高大上的一種了，也是第五種深入思考封恰。既然我們可以通過(guò)runtime找到一個(gè)屬性麻养，那么我們也可以通過(guò)runtime給他動(dòng)態(tài)添加屬性∨堤颍可以為T(mén)extView分類(lèi)動(dòng)態(tài)添加屬性鳖昌，無(wú)需繼承，用法方便低飒。

@interface UITextView (SYJText)

/**
 *  UITextView+placeholder
 */
@property (nonatomic, copy) NSString *syj_placeHolder;
/**
 *  IQKeyboardManager等第三方框架會(huì)讀取placeholder屬性并創(chuàng)建UIToolbar展示
 */
@property (nonatomic, copy) NSString *placeholder;
/**
 *  placeHolder顏色
 */
@property (nonatomic, strong) UIColor *syj_placeHolderColor;


@end

#.m

static const void *syj_placeHolderKey;
@interface UITextView ()
@property (nonatomic, readonly) UILabel *syj_placeHolderLabel;
@end

@implementation UITextView (SYJText)

+(void)load{
    [super load];
    
    //方法交換
    method_exchangeImplementations(class_getInstanceMethod(self.class, NSSelectorFromString(@"layoutSubviews")),
                                   class_getInstanceMethod(self.class, @selector(SYJPlaceHolder_swizzling_layoutSubviews)));
    method_exchangeImplementations(class_getInstanceMethod(self.class, NSSelectorFromString(@"dealloc")),
                                   class_getInstanceMethod(self.class, @selector(SYJPlaceHolder_swizzled_dealloc)));
    method_exchangeImplementations(class_getInstanceMethod(self.class, NSSelectorFromString(@"setText:")),
                                   class_getInstanceMethod(self.class, @selector(SYJPlaceHolder_swizzled_setText:)));
}

#pragma mark - swizzling

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

- (void)SYJPlaceHolder_swizzling_layoutSubviews{
    if (self.syj_placeHolder) {
        UIEdgeInsets textContainerInset = self.textContainerInset;
        CGFloat lineFragmentPadding = self.textContainer.lineFragmentPadding;
        CGFloat x = lineFragmentPadding + textContainerInset.left + self.layer.borderWidth;
        CGFloat y = textContainerInset.top + self.layer.borderWidth;
        CGFloat width = CGRectGetWidth(self.bounds) - x - textContainerInset.right - 2*self.layer.borderWidth;
        CGFloat height = [self.syj_placeHolderLabel sizeThatFits:CGSizeMake(width, 0)].height;
        self.syj_placeHolderLabel.frame = CGRectMake(x, y, width, height);
    }
    [self SYJPlaceHolder_swizzling_layoutSubviews];
}
- (void)SYJPlaceHolder_swizzled_setText:(NSString *)text{
    [self SYJPlaceHolder_swizzled_setText:text];
    if (self.syj_placeHolder) {
        [self updatePlaceHolder];
    }
}
#pragma mark - associated

//動(dòng)態(tài)添加屬性
//綁定syj_placeHolder屬性,作為textview的占位符
-(NSString *)syj_placeHolder{
    return objc_getAssociatedObject(self, &syj_placeHolderKey);
}
-(void)setSyj_placeHolder:(NSString *)syj_placeHolder{
    objc_setAssociatedObject(self, &syj_placeHolderKey, syj_placeHolder, OBJC_ASSOCIATION_RETAIN_NONATOMIC);
    [self updatePlaceHolder];
}
-(UIColor *)syj_placeHolderColor{
    return self.syj_placeHolderLabel.textColor;
}
-(void)setSyj_placeHolderColor:(UIColor *)syj_placeHolderColor{
    self.syj_placeHolderLabel.textColor = syj_placeHolderColor;
}
-(NSString *)placeholder{
    return self.syj_placeHolder;
}
-(void)setPlaceholder:(NSString *)placeholder{
    self.syj_placeHolder = placeholder;
}

#pragma mark - update
- (void)updatePlaceHolder{
    if (self.text.length) {
        [self.syj_placeHolderLabel removeFromSuperview];
        return;
    }
    self.syj_placeHolderLabel.font = self.font?self.font:self.cacutDefaultFont;
    self.syj_placeHolderLabel.textAlignment = self.textAlignment;
    self.syj_placeHolderLabel.text = self.syj_placeHolder;
    [self insertSubview:self.syj_placeHolderLabel atIndex:0];
}

#pragma mark - lazzing
-(UILabel *)syj_placeHolderLabel{
    UILabel *placeHolderLab = objc_getAssociatedObject(self, @selector(syj_placeHolderLabel));
    if (!placeHolderLab) {
        placeHolderLab = [[UILabel alloc] init];
        placeHolderLab.numberOfLines = 0;
        placeHolderLab.textColor = [UIColor lightGrayColor];
        objc_setAssociatedObject(self, @selector(syj_placeHolderLabel), placeHolderLab, OBJC_ASSOCIATION_RETAIN);
        [[NSNotificationCenter defaultCenter] addObserver:self selector:@selector(updatePlaceHolder) name:UITextViewTextDidChangeNotification object:self];
    }
    return placeHolderLab;
}
- (UIFont *)cacutDefaultFont{
    static UIFont *font = nil;
    static dispatch_once_t onceToken;
    dispatch_once(&onceToken, ^{
        UITextView *textview = [[UITextView alloc] init];
        textview.text = @" ";
        font = textview.font;
    });
    return font;
}


@end

 //利用runtime黑魔法及動(dòng)態(tài)添加屬性對(duì)textview添加placeHolder屬性
    UITextView *text = [[UITextView alloc]initWithFrame:CGRectMake(10, 100, [UIScreen mainScreen].bounds.size.width - 20, 240)];
    [self.view addSubview:text];
    text.backgroundColor = [UIColor grayColor];
    //設(shè)置大小要在font設(shè)置place前邊
    text.font = [UIFont boldSystemFontOfSize:16];
    text.syj_placeHolder = @"這個(gè)方法更加的友好,只需引入頭文件,所有文件就能直接使用占位符,不用集成其他類(lèi),建議使用這種方法";
    text.syj_placeHolderColor = [UIColor lightGrayColor];

看下各種的效果

TextView占位符

代碼上傳到github许昨，有需要可以看一下。
https://github.com/SYJshang/TextViewPlaceHolder