带提示（hint）的多行文本输入--UITextView

- (void) viewDidLoad {
    //...
    comments.text = @"请输入：";
    comments.textColor = [UIColor lightGrayColor];
    isEmpty = YES;
    //...
}
- (BOOL)textViewShouldBeginEditing:(UITextView*)textView {
    if (isEmpty) {
        comments.text = @"";
        comments.textColor = [UIColor blackColor];
        isEmpty = NO;
    }
    return YES;
}
- (void) textViewDidEndEditing:(UITextView*)textView {
    if(comments.text.length == 0){
        comments.textColor = [UIColor lightGrayColor];
        comments.text = @"请输入：";
        isEmpty = YES;
    }
}
注意：需要在.h文件种添加协议<UITextViewDelegate>,在.m文件种设置协议 comments.delegate=self;