改变 UITextField 提示语的 字体颜色

<pre name="code" class="objc">//第一种       UIColor *color = [UIColor whiteColor];      _userName.attributedPlaceholder = [[NSAttributedString alloc] initWithString:@"用户名" attributes:@{NSForegroundColorAttributeName: color}];      //第二种   [_userName setValue:[UIColor whiteColor] forKeyPath:@"_placeholderLabel.textColor"];  

[textField setValue:[UIFont boldSystemFontOfSize:16] forKeyPath:@"_placeholderLabel.font"];