关于UITextField和UITextView的placeholder

1. 大家都知道UITextField支持设置placeholder, 并且可以改变placeholder字体大小和颜色, 参照代码:

/* 设置placeholder*/
[textField setPlaceholder:@"placeholder in textField"];

/* 改变placeholder的颜色 */
[textField setValue:[UIColor redColor] forKeyPath:@"_placeholderLabel.textColor"];  

/* 改变placeholder的字体大小 */
[textField setValue:[UIFont systemFontOfSize:20.f] forKeyPath:@"_placeholderLabel.font"];

2. UITextView是不支持placeholder, 不过没事, 我们可以手动添加一个label, 设置字体大小颜色就只需要操作label即可:

/* 添加UITextView */
UITextView *textView = [[UITextView alloc] initWithFrame:CGRectMake(0, 0, 320.f, 47.f)];
textView.delegate = self;        //
textView.backgroundColor = [UIColor clearColor];
[self addSubView:textView];

/* 添加placeholder Label */
UILabel *placeHolderLabel = [[UILabel alloc] initWithFrame:CGRectZero];
placeHolderLabel.textColor = [UIColor lightGrayColor];
placeHolderLabel.text = @"placeholder in textView";
[placeHolderLabel sizeToFit];
placeHolderLabel.frame = CGRectMake(0, 5.f, placeHolderLabel.frame.size.width, placeHolderLabel.frame.size.height);
[self addSubView:placeHolderLabel];

/* 监听textView发生变化, 无内容则显示placeholder */
- (void)textViewDidChange:(UITextView *)textView{
    if ([[textView.text stringByTrimmingCharactersInSet:[NSCharacterSet whitespaceAndNewlineCharacterSet]] isEqualToString:@""]) {
        placeHolderLabel.text = @"placeholder in textView";
    }else{
        placeHolderLabel.text = @"";
    }
}