// .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,用的的時候才會去加載// 需要給系統UITextField添加屬性,只能使用runtime- (void)setPlaceholderColor:(UIColor *)placeholderColor{ // 設置關聯 objc_setAssociatedObject(self,(__bridge const void *)(placeholderColorName), placeholderColor, OBJC_ASSOCIATION_RETAIN_NONATOMIC); // 設置占位文字顏色 UILabel *placeholderLabel = [self valueForKeyPath:@"placeholderLabel"]; placeholderLabel.textColor = placeholderColor;}- (UIColor *)placeholderColor{ // 返回關聯 return objc_getAssociatedObject(self, (__bridge const void *)(placeholderColorName));}// 設置占位文字,并且設置占位文字顏色- (void)bs_setPlaceholder:(NSString *)placeholder{ // 1.設置占位文字 [self bs_setPlaceholder:placeholder]; // 2.設置占位文字顏色 self.placeholderColor = self.placeholderColor;}@end