UITextView添加占位字符

迈不过友情╰ 2022-08-10 09:42 139阅读 0赞

\#import "YGTextView.h"  
  
\#define kPlaceholderDefaultTopMargin 4     // Placeholder上下间距  
\#define kPlaceholderDefaultLeftMargin 5    // Placeholder左右间距  
@implementation YGTextView  
  
\#pragma mark - 初始化PlaceholderTextView  
\- (instancetype)initWithFrame:(CGRect)frame  
\{  
    self = \[super initWithFrame:frame\];  
      
    if (self)  
    \{  
        self.opaque = YES;  
          
        // 设置通知, 当TextView文字发生改变时, 向自己发送通知  
        \[\[NSNotificationCenter defaultCenter\] addObserver:self selector:@selector(textDidChanged) name:UITextViewTextDidChangeNotification object:self\];  
    \}  
      
    return self;  
\}  
  
\#pragma mark - 通知事件  
\- (void)textDidChanged  
\{  
    // 重新绘制  
    \[self setNeedsDisplay\];  
\}  
  
\#pragma mark - 重写属性方法, 实时绘制  
\- (void)setPlaceholder:(NSString \*)placeholder  
\{  
    \_placeholder = \[placeholder copy\];  
      
    \[self setNeedsDisplay\];  
\}  
  
\- (void)setPlaceholderColor:(UIColor \*)placeholderColor  
\{  
    \_placeholderColor = placeholderColor;  
      
    \[self setNeedsDisplay\];  
\}  
  
\- (void)setText:(NSString \*)text  
\{  
    \[super setText:text\]; // 系统自带属性  
      
    \[self setNeedsDisplay\];  
\}  
  
\- (void)setAttributedText:(NSAttributedString \*)attributedText  
\{  
    \[super setAttributedText:attributedText\];  
      
    \[self setNeedsDisplay\];  
\}  
  
\- (void)setFont:(UIFont \*)font  
\{  
    \[super setFont:font\];  
      
    // 会在下一个消息循环调用drawRect  
    \[self setNeedsDisplay\];  
\}  
  
\#pragma mark - 绘制子控件  
\- (void)drawRect:(CGRect)rect  
\{  
    // 若TextView有文字  
    if (self.hasText)  
    \{  
        return;  
    \}  
      
    // 文字属性  
    NSMutableDictionary \*attrs = \[NSMutableDictionary dictionary\];  
    attrs\[NSFontAttributeName\] = self.font; // 获取当前PlaceholderTextView的文字属性  
    attrs\[NSForegroundColorAttributeName\] = self.placeholderColor ? self.placeholderColor : \[UIColor lightGrayColor\];  
      
    // 绘制范围  
    CGFloat placeholderTopMargin = self.placeholderTopMargin ? self.placeholderTopMargin : kPlaceholderDefaultTopMargin;  
    CGFloat placeholderLeftMargin = self.placeholderLeftMargin ? self.placeholderLeftMargin : kPlaceholderDefaultTopMargin;  
      
    CGFloat placeholderX = placeholderTopMargin;  
    CGFloat placeholderY = placeholderLeftMargin;  
    CGFloat placeholderW = rect.size.width - 2 \* placeholderLeftMargin;  
    CGFloat placeholderH = rect.size.height - 2 \* placeholderTopMargin;  
    CGRect placeholderRect = CGRectMake(placeholderX, placeholderY, placeholderW, placeholderH);  
      
    \[self.placeholder drawInRect:placeholderRect withAttributes:attrs\];  
\}  
  
\#pragma mark - 移除通知  
\- (void)dealloc  
\{  
    \[\[NSNotificationCenter defaultCenter\] removeObserver:self\];  
\}  
  
@end