自定义控件注意或框架注意:自己暴露在外面的属性,一定要重写setter,保证外界与内部的交互性

一.方案一:通过drawRect:方法将文字画到textView中,监听文字改变用的是通知中心(代理也可以监听文字改变,但是这种方式就成了自己作为自己的代理了,不推荐这种方法)发出的消息

UITextViewTextDidChangeNotification.自己监听通知.

• 对外界提供两个属性

• 内部实现

1 #import "ChaosPlaceholdTextView.h" 2  3 @implementation ChaosPlaceholdTextView 4  5 - (instancetype)initWithFrame:(CGRect)frame 6 { 7     if (self = [super initWithFrame:frame]) { 8          9         [[NSNotificationCenter defaultCenter] addObserver:self selector:@selector(textChange) name:UITextViewTextDidChangeNotification object:nil];10         11         // 外界文字颜色不设置,默认为灰色12         self.placeholdColor = [UIColor grayColor];13     }14     return self;15 }16 17 - (void)dealloc18 {19     [[NSNotificationCenter defaultCenter] removeObserver:self];20 }21 22 - (void)textChange23 {24     [self setNeedsDisplay];25 }26 27 // 调用drawRect时,会将之前的图像擦除掉,重新绘制28 - (void)drawRect:(CGRect)rect {29     30     if ([self hasText]) return;31     32     rect.origin.y += (64 + 7);33     rect.origin.x += 5;34     rect.size.width -= 2 * rect.origin.x;35     36     NSMutableDictionary *attrs = [NSMutableDictionary dictionary];37     attrs[NSForegroundColorAttributeName] = self.placeholdColor;38     attrs[NSFontAttributeName] = [UIFont systemFontOfSize:17];39     [self.placehold drawInRect:rect withAttributes:attrs];40 }41 42 // 设计框架需注意,给外界提供了属性后,一定重写出行的setter,这样既可以时时监听使用者对属性的更改,还可以跟好的与外界代码进行交互43 - (void)setPlacehold:(NSString *)placehold44 {45     _placehold = placehold;46     // 设置了站位文字后,需要重绘一遍47     [self setNeedsDisplay];48 }49 50 - (void)setPlaceholdColor:(UIColor *)placeholdColor51 {52     _placeholdColor = placeholdColor;53     [self setNeedsDisplay];54 }55 56 // 同时,也要考虑到57 - (void)setFont:(UIFont *)font58 {59     [super setFont:font];60     61     [self setNeedsDisplay];62 }63 64 - (void)setText:(NSString *)text65 {66     [super setText:text];67     68     [self setNeedsDisplay];69 }70 71 - (void)setAttributedText:(NSAttributedString *)attributedText72 {73     [super setAttributedText:attributedText];74     75     [self setNeedsDisplay];76 }77 78 @end

• 缺点:由于是画上去的,当设置了textView的alwaysBounceHorizontal属性后,不能跟随着scrollView的滑动而滑动,如下图

方案二:通过给TextView添加一个Label,也是通过监听文字改变的通知,修改label的hidden属性.

1 #import "ChaosPlaceholdTextView.h"  2   3 @interface ChaosPlaceholdTextView()  4 /** 占位文字label */  5 @property (nonatomic, weak) UILabel *placeholderLabel;  6 @end  7   8 @implementation ChaosPlaceholdTextView  9  10 - (UILabel *)placeholderLabel 11 { 12     if (!_placeholderLabel) { 13         // 添加一个用来显示占位文字的label 14         UILabel *placeholderLabel = [[UILabel alloc] init]; 15         placeholderLabel.numberOfLines = 0; 16         placeholderLabel.x = 4; 17         placeholderLabel.y = 7; 18         [self addSubview:placeholderLabel]; 19         _placeholderLabel = placeholderLabel; 20     } 21     return _placeholderLabel; 22 } 23  24 - (instancetype)initWithFrame:(CGRect)frame 25 { 26     if (self = [super initWithFrame:frame]) { 27         // 垂直方向上永远有弹簧效果 28         self.alwaysBounceVertical = YES; 29          30         // 默认字体 31         self.font = [UIFont systemFontOfSize:15]; 32          33         // 默认的占位文字颜色 34         self.placeholderColor = [UIColor grayColor]; 35          36         // 监听文字改变 37         [[NSNotificationCenter defaultCenter] addObserver:self selector:@selector(textDidChange) name:UITextViewTextDidChangeNotification object:nil]; 38     } 39     return self; 40 } 41  42 - (void)dealloc 43 { 44     [[NSNotificationCenter defaultCenter] removeObserver:self]; 45 } 46  47 /** 48  * 监听文字改变 49  */ 50 - (void)textDidChange 51 { 52     // 只要有文字, 就隐藏占位文字label 53     self.placeholderLabel.hidden = self.hasText; 54 } 55  56 /** 57  * 更新占位文字的尺寸 58  */ 59 - (void)updatePlaceholderLabelSize 60 { 61     CGSize maxSize = CGSizeMake(ChaosScreenW - 2 * self.placeholderLabel.x, MAXFLOAT); 62     self.placeholderLabel.size = [self.placeholder boundingRectWithSize:maxSize options:NSStringDrawingUsesLineFragmentOrigin attributes:@{NSFontAttributeName : self.font} context:nil].size; 63 } 64  65 #pragma mark - 重写setter 66 - (void)setPlaceholderColor:(UIColor *)placeholderColor 67 { 68     _placeholderColor = placeholderColor; 69      70     self.placeholderLabel.textColor = placeholderColor; 71 } 72  73 - (void)setPlaceholder:(NSString *)placeholder 74 { 75     _placeholder = [placeholder copy]; 76      77     self.placeholderLabel.text = placeholder; 78      79     [self updatePlaceholderLabelSize]; 80 } 81  82 - (void)setFont:(UIFont *)font 83 { 84     [super setFont:font]; 85      86     self.placeholderLabel.font = font; 87      88     [self updatePlaceholderLabelSize]; 89 } 90  91 - (void)setText:(NSString *)text 92 { 93     [super setText:text]; 94      95     [self textDidChange]; 96 } 97  98 - (void)setAttributedText:(NSAttributedString *)attributedText 99 {100     [super setAttributedText:attributedText];101     102     [self textDidChange];103 }104 105 @end