本文主要通过runtime实现将UIApplicationDelegate方法在AppDelegate类中提取出来，这样避免AppDelegate类变得冗余，可以将UIApplicationDelegate方法中需要处理的逻辑代码剥离出来，单独处理，实现代码低耦合。
- 创建UIApplication的category分类，获取UIApplication的delegate.
+ (void)load
{
SEL systemSelector = @selector(setDelegate:);
SEL customSelector = @selector(nl_setDelegate:);
Method systemMethod = class_getInstanceMethod([self class], systemSelector);
Method customMethod = class_getInstanceMethod([self class], customSelector);
method_exchangeImplementations(systemMethod, customMethod);
}
- (void)nl_setDelegate:(id<UIApplicationDelegate>)delegate
{
//获取UIApplication的delegate
[UIApplication exchangeMethods:delegate];
[self nl_setDelegate:delegate];
}
- 为UIApplicationDelegate 的方法添加默认实现
由于UIApplicationDelegate协议中的方法都是可选的，所以AppDelegate类中可能没有所需方法的实现，这时候我们要为方法添加默认实现。这里我们拿 -(void)applicationDidEnterBackground:(UIApplication *)application方法为例，代码如下
//这里delegateClass 默认是AppDelegate类，但是如果项目修改AppDelegate的类名，这里相应做改变。
Class delegateClass = object_getClass(delegate);
SEL delegateSelector = @selector(applicationDidEnterBackground:);
SEL defaultSelector = @selector(default_applicationDidEnterBackground:);
IMP defaultImp = class_getMethodImplementation([self class], defaultSelector);
class_addMethod(delegateClass, delegateSelector, defaultImp, nil);
- (void)default_applicationDidEnterBackground:(UIApplication *)application
{
}
- 为UIApplicationDelegate 的方法添加自定义方法实现
Class delegateClass = object_getClass(delegate);
SEL customSelector = @selector(custom_applicationDidEnterBackground:);
IMP customImp = class_getMethodImplementation([self class], customSelector);
class_addMethod(delegateClass, customSelector, customImp, nil);
- 交换AppDelegate方法实现和自定义方法实现
Method systemMethod = class_getInstanceMethod(delegateClass, delegateSelector);
Method newMethod = class_getInstanceMethod(delegateClass, customSelector);
method_exchangeImplementations(systemMethod, newMethod);
- 获取UIApplicationDelegate方法回调
- (void)custom_applicationDidEnterBackground:(UIApplication *)application
{
[self custom_applicationDidEnterBackground:application];
//此处获取UIApplicationDelegate 方法 applicationDidEnterBackground:application 回调。
}
- 获取UIApplicationDelegate方法，并发送自定义通知，这样可以在项目中任何地方可以监测应用程序状态，并实现自定义逻辑代码
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