Objective-C Runtime之着魔的UIAlertView

前言：

上篇文章写的是Runtime的一个入门教程，刚哥问我那个Associated Objects加回调是啥时候用，那我就来告诉你啦！我们在使用UIAlertView的时候用的多。

传统的UIAlertView：

在一个类中有多个UIAlertView，不同的UIAlertView对应不同的事件，我们使用的传统方法如下：

#pragma mark - action method

- (IBAction)firstButtonClick:(id)sender {
    UIAlertView *alertView = [[UIAlertView alloc] initWithTitle:@"title" message:@"message" delegate:self cancelButtonTitle:@"cancel" otherButtonTitles:@"ok", nil];
    alertView.tag = 1001;
    [alertView show];
}

- (IBAction)secondButtonClick:(id)sender {
    UIAlertView *alertView = [[UIAlertView alloc] initWithTitle:@"title" message:@"message" delegate:self cancelButtonTitle:@"cancel" otherButtonTitles:@"ok", nil];
    alertView.tag = 1002;
    [alertView show];
}

- (IBAction)ThirdButtonClick:(id)sender {
    UIAlertView *alertView = [[UIAlertView alloc] initWithTitle:@"title" message:@"message" delegate:self cancelButtonTitle:@"cancel" otherButtonTitles:@"ok", nil];
    alertView.tag = 1003;
    [alertView show];
}

#pragma mark - delegate method

- (void)alertView:(UIAlertView *)alertView clickedButtonAtIndex:(NSInteger)buttonIndex
{
    if (alertView.tag == 1001) {
        if (buttonIndex == 1) {
            NSLog(@"普通alertView1001执行ok");
        }
    } else if (alertView.tag == 1002) {
        if (buttonIndex == 1) {
            NSLog(@"普通alertView1002执行ok");
        }
    } else if (alertView.tag == 1003) {
        if (buttonIndex == 1) {
            NSLog(@"普通alertView1003执行ok");
        }
    }
}

我们要给每个UIAlertView赋值一个tag值，在delegate方法中还要进行tag的判断以及buttonIndex的判断，太繁琐了。

着魔的UIAlertView：

下面我们使用Category和Associated Objects进行魔法修改

创建一个UIAlertView的Category

UIAlertView+ActionBlock.h

#import <UIKit/UIKit.h>

typedef void (^AlertCallBack)(UIAlertView *, NSUInteger);

@interface UIAlertView (ActionBlock)<UIAlertViewDelegate>

@property (nonatomic, copy) AlertCallBack callBack;

@end

UIAlertView+ActionBlock.m

#if TARGET_IPHONE_SIMULATOR
#import <objc/objc-runtime.h>
#else
#import <objc/runtime.h>
#import <objc/message.h>
#endif

@implementation UIAlertView (ActionBlock)

- (void)setCallBack:(AlertCallBack)callBack
{
    objc_setAssociatedObject(self, @selector(callBack), callBack, OBJC_ASSOCIATION_COPY_NONATOMIC);
    self.delegate = self;
}

- (AlertCallBack)callBack
{
    return objc_getAssociatedObject(self, @selector(callBack));
}

#pragma mark - delegate method

- (void)alertView:(UIAlertView *)alertView clickedButtonAtIndex:(NSInteger)buttonIndex
{
    if (self.callBack) {
        self.callBack(alertView, buttonIndex);
    }
}

在主类中取消delegate，使用block属性

#pragma mark - action method

- (IBAction)firstButtonClick:(id)sender {
    UIAlertView *alertView = [[UIAlertView alloc] initWithTitle:@"title" message:@"message" delegate:self cancelButtonTitle:@"cancel" otherButtonTitles:@"ok", nil];
    alertView.callBack = ^(UIAlertView *alertView, NSUInteger buttonIndex){
        if (buttonIndex == 1) {
            NSLog(@"魔法alertView1001执行ok");
        }
    };
    [alertView show];
}

- (IBAction)secondButtonClick:(id)sender {
    UIAlertView *alertView = [[UIAlertView alloc] initWithTitle:@"title" message:@"message" delegate:self cancelButtonTitle:@"cancel" otherButtonTitles:@"ok", nil];
    alertView.callBack = ^(UIAlertView *alertView, NSUInteger buttonIndex){
        if (buttonIndex == 1) {
            NSLog(@"魔法alertView1002执行ok");
        }
    };
    [alertView show];
}

- (IBAction)ThirdButtonClick:(id)sender {
    UIAlertView *alertView = [[UIAlertView alloc] initWithTitle:@"title" message:@"message" delegate:self cancelButtonTitle:@"cancel" otherButtonTitles:@"ok", nil];
    alertView.callBack = ^(UIAlertView *alertView, NSUInteger buttonIndex){
        if (buttonIndex == 1) {
            NSLog(@"魔法alertView1003执行ok");
        }
    };
    [alertView show];
}

我们通过使用Category给UIAlertView扩展了一个block属性，当block被设置后就会调用setCallBack方法，触发self.delegate = self，即主类中的UIAlertView的delegate方法被Category中的方法覆盖。这样不仅有效解决问题，还解决了其他人修改该类的安全性（block被去掉后，原delegate恢复）

如下不给tag值为1003的UIAlertView设置block，即调用原delegate方法。

- (IBAction)firstButtonClick:(id)sender {
    UIAlertView *alertView = [[UIAlertView alloc] initWithTitle:@"title" message:@"message" delegate:self cancelButtonTitle:@"cancel" otherButtonTitles:@"ok", nil];
    alertView.callBack = ^(UIAlertView *alertView, NSUInteger buttonIndex){
        if (buttonIndex == 1) {
            NSLog(@"魔法alertView1001执行ok");
        }
    };
    alertView.tag = 1001;
    [alertView show];
}

- (IBAction)secondButtonClick:(id)sender {
    UIAlertView *alertView = [[UIAlertView alloc] initWithTitle:@"title" message:@"message" delegate:self cancelButtonTitle:@"cancel" otherButtonTitles:@"ok", nil];
    alertView.callBack = ^(UIAlertView *alertView, NSUInteger buttonIndex){
        if (buttonIndex == 1) {
            NSLog(@"魔法alertView1002执行ok");
        }
    };
    alertView.tag = 1002;
    [alertView show];
}

- (IBAction)ThirdButtonClick:(id)sender {
    UIAlertView *alertView = [[UIAlertView alloc] initWithTitle:@"title" message:@"message" delegate:self cancelButtonTitle:@"cancel" otherButtonTitles:@"ok", nil];
    alertView.tag = 1003;
    [alertView show];
}

- (IBAction)fourthButtonClick:(id)sender {
    UIAlertController *alertController = [UIAlertController alertControllerWithTitle:@"title" message:@"message" preferredStyle:UIAlertControllerStyleAlert];
    UIAlertAction *cancelAction = [UIAlertAction actionWithTitle:@"cancel" style:UIAlertActionStyleCancel handler:nil];
    UIAlertAction *okAction = [UIAlertAction actionWithTitle:@"ok" style:UIAlertActionStyleDefault handler:^(UIAlertAction *alertAction){
        NSLog(@"如果你是iOS8以上的应用，这个适合你，简单明了");
    }];
    [alertController addAction:cancelAction];
    [alertController addAction:okAction];
    [self presentViewController:alertController animated:YES completion:nil];
}

#pragma mark - delegate method

- (void)alertView:(UIAlertView *)alertView clickedButtonAtIndex:(NSInteger)buttonIndex
{
    if (alertView.tag == 1001) {
        if (buttonIndex == 1) {
            NSLog(@"普通alertView1001执行ok");
        }
    } else if (alertView.tag == 1002) {
        if (buttonIndex == 1) {
            NSLog(@"普通alertView1002执行ok");
        }
    } else if (alertView.tag == 1003) {
        if (buttonIndex == 1) {
            NSLog(@"普通alertView1003执行ok");
        }
    } else if (alertView.tag == 1004) {
        if (buttonIndex == 1) {
            NSLog(@"普通alertView1004执行ok");
        }
    }
}

相关Demo下载：

https://github.com/ianisme/UIAlertViewBYRuntime_Demo

总结：

通过Associated Objects我们有效的解决了UIAlertView的繁琐问题，如果您是开发iOS8以上的应用，建议您弃用UIAlertView，苹果的UIAlertController已经有了更好的解决方案。