转自：http://m.2cto.com/kf/201608/534005.html
流程：
1.创建textView
2.给textView添加一个UILabel子控件，作为placeholder
3.在文本改变的代理方法里面显示/隐藏UILabel
特点：
该方法同样也可以实现类似于placeholder的功能。相比较方法一，方法二可以实现动态监听文本的改变，并非弹出键盘就立即清除placeholder，只有当用户开始输入文本的时候。placeholder才会消失。同样，当用户清空文本的时候，placeholder又会重新显示出来。
代理：<UITextViewDelegate>
pragma mark - 绘制 发布 界面
-
(void)createPublishView{
UITextView * textView = [[UITextView alloc]init];
self.textView = textView;
[self.backgroundView addSubview:_textView];[_textView mas_makeConstraints:^(MASConstraintMaker *make) {
make.left.right.top.mas_equalTo(0); make.height.mas_equalTo(74);}];
_textView.backgroundColor = [UIColor redColor];
_textView.delegate = self;
[self setupPlaceHolder];
}
// 给textView添加一个UILabel子控件
-
(void)setupPlaceHolder {
UILabel *placeHolder = [[UILabel alloc] init];
self.placeHolder = placeHolder;
[self.textView addSubview:placeHolder];[_placeHolder mas_makeConstraints:^(MASConstraintMaker *make) {
make.left.mas_equalTo(15); make.top.mas_equalTo(12); make.height.mas_equalTo(20);}];
placeHolder.backgroundColor = [UIColor yellowColor];
placeHolder.text = @"说点什么吧...";
placeHolder.textColor = [UIColor lightGrayColor];
placeHolder.numberOfLines = 0;
placeHolder.contentMode = UIViewContentModeTop;
placeHolder.font = [UIFont jk_systemFontOfPxSize:14];
}
pragma mark - TextView 代理 & 数据源
-
(void)textViewDidChange:(UITextView *)textView {
if (!textView.text.length) {
self.placeHolder.alpha = 1;
} else {
self.placeHolder.alpha = 0;
}
}
//关闭键盘
-(void) dismissKeyBoard{[self.textView resignFirstResponder];
}
