iOS13 禁止textfield通过KVC获取和修改私有属性

• UITextField

在ios 13之前，UITextField可以通过KVC修改属性

//字体颜色

[textField setValue:[UIColor whiteColor]forKeyPath:@"_placeholderLabel.textColor"];

//字体大小

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

//水平居中

[textField setValue:[NSNumber numberWithInteger:NSTextAlignmentCenter] forKeyPath:@"_placeholderLabel.textAlignment"];

在ios 13之后，UITextField禁止通过KVC修改属性，以下提供两种方式

解决方式1：通过attributedPlaceholder属性修改Placeholder颜色

NSAttributedString *attrString = [[NSAttributedString alloc] initWithString:@"请输入占位文字" attributes: @{NSForegroundColorAttributeName:[UIColor redColor], NSFontAttributeName:textField.font }];

textField.attributedPlaceholder = attrString;

解决方式2：为UITextField重新写一个方法

- (void)resetTextField:(UITextField *)textField{
 	Ivar ivar =  class_getInstanceVariable([textField class], "_placeholderLabel");

    UILabel *placeholderLabel = object_getIvar(textField, ivar);

    placeholderLabel.text = title;

    placeholderLabel.textColor = color;

    placeholderLabel.font = [UIFont systemFontOfSize:fontSize];

    placeholderLabel.textAlignment = alignment;
}