iOS开发小技巧--自定义带有占位文字的TextView(两种方式)

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

#import "ChaosPlaceholdTextView.h"

@implementation ChaosPlaceholdTextView

- (instancetype)initWithFrame:(CGRect)frame
{
    if (self = [super initWithFrame:frame]) {
        
        [[NSNotificationCenter defaultCenter] addObserver:self selector:@selector(textChange) name:UITextViewTextDidChangeNotification object:nil];
        
        // 外界文字颜色不设置,默认为灰色
        self.placeholdColor = [UIColor grayColor];
    }
    return self;
}

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

- (void)textChange
{
    [self setNeedsDisplay];
}

// 调用drawRect时,会将之前的图像擦除掉,重新绘制
- (void)drawRect:(CGRect)rect {
    
    if ([self hasText]) return;
    
    rect.origin.y += (64 + 7);
    rect.origin.x += 5;
    rect.size.width -= 2 * rect.origin.x;
    
    NSMutableDictionary *attrs = [NSMutableDictionary dictionary];
    attrs[NSForegroundColorAttributeName] = self.placeholdColor;
    attrs[NSFontAttributeName] = [UIFont systemFontOfSize:17];
    [self.placehold drawInRect:rect withAttributes:attrs];
}

// 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
- (void)setPlacehold:(NSString *)placehold
{
    _placehold = placehold;
    // 设置了站位文字后,需要重绘一遍
    [self setNeedsDisplay];
}

- (void)setPlaceholdColor:(UIColor *)placeholdColor
{
    _placeholdColor = placeholdColor;
    [self setNeedsDisplay];
}

// 同时,也要考虑到
- (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

• 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.

#import "ChaosPlaceholdTextView.h"

@interface ChaosPlaceholdTextView()
/** 占位文字label */
@property (nonatomic, weak) UILabel *placeholderLabel;
@end

@implementation ChaosPlaceholdTextView

- (UILabel *)placeholderLabel
{
    if (!_placeholderLabel) {
        // 添加一个用来显示占位文字的label
        UILabel *placeholderLabel = [[UILabel alloc] init];
        placeholderLabel.numberOfLines = 0;
        placeholderLabel.x = 4;
        placeholderLabel.y = 7;
        [self addSubview:placeholderLabel];
        _placeholderLabel = placeholderLabel;
    }
    return _placeholderLabel;
}

- (instancetype)initWithFrame:(CGRect)frame
{
    if (self = [super initWithFrame:frame]) {
        // 垂直方向上永远有弹簧效果
        self.alwaysBounceVertical = YES;
        
        // 默认字体
        self.font = [UIFont systemFontOfSize:15];
        
        // 默认的占位文字颜色
        self.placeholderColor = [UIColor grayColor];
        
        // 监听文字改变
        [[NSNotificationCenter defaultCenter] addObserver:self selector:@selector(textDidChange) name:UITextViewTextDidChangeNotification object:nil];
    }
    return self;
}

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

/**
 * 监听文字改变
 */
- (void)textDidChange
{
    // 只要有文字, 就隐藏占位文字label
    self.placeholderLabel.hidden = self.hasText;
}

/**
 * 更新占位文字的尺寸
 */
- (void)updatePlaceholderLabelSize
{
    CGSize maxSize = CGSizeMake(ChaosScreenW - 2 * self.placeholderLabel.x, MAXFLOAT);
    self.placeholderLabel.size = [self.placeholder boundingRectWithSize:maxSize options:NSStringDrawingUsesLineFragmentOrigin attributes:@{NSFontAttributeName : self.font} context:nil].size;
}

#pragma mark - 重写setter
- (void)setPlaceholderColor:(UIColor *)placeholderColor
{
    _placeholderColor = placeholderColor;
    
    self.placeholderLabel.textColor = placeholderColor;
}

- (void)setPlaceholder:(NSString *)placeholder
{
    _placeholder = [placeholder copy];
    
    self.placeholderLabel.text = placeholder;
    
    [self updatePlaceholderLabelSize];
}

- (void)setFont:(UIFont *)font
{
    [super setFont:font];
    
    self.placeholderLabel.font = font;
    
    [self updatePlaceholderLabelSize];
}

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

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

@end