今天在适配iOS13的时候发现像获取或设置UITextField的PlaceHolder崩溃，造成崩溃的原因是如下这样的写法，现在被系统禁止使用了

color = [textField valueForKeyPath:@"_placeholderLabel.textColor"];

现在正确的写法如下

 UITextField *textField = [[UITextField alloc] init];
  textField.placeholder = @" ";
  Ivar ivar = class_getInstanceVariable([UITextField class], "_placeholderLabel");
  UILabel *placehoderLabel = object_getIvar(textField, ivar);
  color = placehoderLabel.textColor;

通过运行时来获取系统是允许这样做的，亲测可用。

以上是Objc版本，现在我们看一下swift如何写

let iVar = class_getInstanceVariable(UITextField.self, "_placeholderLabel")!
 let placeholderLabel = object_getIvar(textField, iVar) as! UILabel
 color = placeholderLabel.textColor