iOS 改变UITextField placeholder颜

iOS11之后，使用UITextField时，它的私有属性_placeholderLabel被禁止访问了。所以我们无法像以前一样使用如下方法改变placeholderLabel的属性了

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

How do we do?

可以利用runtime进行解决。
代码如下：

OC

.h

#import <UIKit/UIKit.h>

NS_ASSUME_NONNULL_BEGIN

@interface HanPlaceholderTextField : UITextField
@property(nonatomic, strong) UIColor *placeholderColor;
@property(nonatomic, strong) UIFont  *placeholderFont;
@end

.m

#import "HanPlaceholderTextField.h"
#import <objc/runtime.h>

@interface HanPlaceholderTextField ()
@end

@implementation HanPlaceholderTextField
-(void)changePlaceholder{
    Ivar ivar = class_getInstanceVariable([UITextField class], "_placeholderLabel");
    UILabel *placeholderLabel = object_getIvar(self, ivar);
    placeholderLabel.textColor = _placeholderColor;
    placeholderLabel.font = _placeholderFont;
}
-(void)setPlaceholderColor:(UIColor *)placeholderColor{
    _placeholderColor = placeholderColor;
    [self changePlaceholder];
}
-(void)setPlaceholder:(NSString *)placeholder{
    [super setPlaceholder:placeholder];
    [self changePlaceholder];
}
-(void)setPlaceholderFont:(UIFont *)placeholderFont{
    _placeholderFont = placeholderFont;
    [self changePlaceholder];
}
@end

用法

...
#import "HanPlaceholderTextField.h"
...

....
HanPlaceholderTextField *textField = [[HanPlaceholderTextField alloc] initWithFrame:CGRectMake(0, 100, [UIScreen mainScreen].bounds.size.width, 40)];
textField.placeholderColor = [UIColor redColor];
textField.placeholderFont = [UIFont systemFontOfSize:10];
textField.textColor = [UIColor blueColor];
textField.placeholder = @"你好";
[self.view addSubview:textField];
....

Swift

import UIKit

class HanPlaceholderTextField: UITextField {
    
    public var placeholderColor:UIColor?{
        didSet{
            self.changePlaceholder();
        }
    }
    public var placeholderFont:UIFont?{
        didSet{
            self.changePlaceholder();
        }
    }
    
    override var placeholder: String?{
        didSet{
            let p = placeholder
            self.changePlaceholder()
            super.placeholder = p
        }
    }

    private func changePlaceholder(){
        let ivar = class_getInstanceVariable(object_getClass(UITextField()), "_placeholderLabel")
        let placeholderLabel  = object_getIvar(self, ivar!) as? UILabel
        placeholderLabel?.textColor = placeholderColor
        placeholderLabel?.font = placeholderFont
    }
    
    

}

用法

import UIKit

class ViewController: UIViewController {

    override func viewDidLoad() {
        super.viewDidLoad()
        // Do any additional setup after loading the view.
        
        
        
        let textField:HanPlaceholderTextField = HanPlaceholderTextField.init(frame: CGRect.init(x: 0, y: 100, width: UIScreen.main.bounds.size.width, height: 44))
        textField.backgroundColor = UIColor.black
        textField.placeholderColor = UIColor.red
        textField.placeholderFont =  UIFont.systemFont(ofSize: 10)
        textField.textColor = UIColor.blue
        textField.placeholder = "你好";
        self.view.addSubview(textField)
    }


}

=====================

发现有一个神奇的属性
textField.attributedPlaceholder
这个属性可以利用富文本改变textField的Placeholder