// .h文件

#import <UIKit/UIKit.h>

@interface UITextField (Placeholder)

@property UIColor *placeholderColor;

@end

// .m文件

#import "UITextField+Placeholder.h"

#import <objc/message.h>

NSString * const placeholderColorName = @"placeholderColor";

@implementation UITextField (Placeholder)

+ (void)load
{
 // 獲取setPlaceholder
 Method setPlaceholder = class_getInstanceMethod(self, @selector(setPlaceholder:));
 // 獲取bs_setPlaceholder
 Method bs_setPlaceholder = class_getInstanceMethod(self, @selector(bs_setPlaceholder:));

 // 交換方法
 method_exchangeImplementations(setPlaceholder, bs_setPlaceholder);
}

// OC最喜歡懶加載,用的的時(shí)候才會(huì)去加載

// 需要給系統(tǒng)UITextField添加屬性,只能使用runtime

- (void)setPlaceholderColor:(UIColor *)placeholderColor
{
 // 設(shè)置關(guān)聯(lián)
 objc_setAssociatedObject(self,(__bridge const void *)(placeholderColorName), placeholderColor, OBJC_ASSOCIATION_RETAIN_NONATOMIC);

 // 設(shè)置占位文字顏色
 UILabel *placeholderLabel = [self valueForKeyPath:@"placeholderLabel"];

 placeholderLabel.textColor = placeholderColor;

}

- (UIColor *)placeholderColor
{
 // 返回關(guān)聯(lián)

 return objc_getAssociatedObject(self, (__bridge const void *)(placeholderColorName));
}

// 設(shè)置占位文字,并且設(shè)置占位文字顏色
- (void)bs_setPlaceholder:(NSString *)placeholder
{
 // 1.設(shè)置占位文字
 [self bs_setPlaceholder:placeholder];


 // 2.設(shè)置占位文字顏色
 self.placeholderColor = self.placeholderColor;

}

@end