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之前在用電池醫生的時候, 發現它有這樣一個功能:當應用進入後臺的時候, 會顯示另外一張圖片覆蓋App Switcher顯示的介面。

效果如下:

變成---->

而這樣的一個功能, 對於保護使用者隱私還是挺有用的。

這就涉及到了Background Fetch的使用。當然, Background Fetch有更多，更有用的功能, 

詳見-->iOS 7學習：多工處理之Background Fetch

下面就介紹下後臺圖片切換的實現。

1.程式配置後臺模式

操作如下:

2. AppDelegate.h新增程式碼:

@property (strong, nonatomic) UIImageView *splashView;

3.AppDelegate.m新增程式碼:

////  AppDelegate.m
 
//  FuckTest////  Created by Colin on 14-4-5.//  Copyright (c) 2014年 icephone. All rights reserved.//#import "AppDelegate.h"@implementation [email protected] splashView;- (BOOL)application:(UIApplication *)application didFinishLaunchingWithOptions:(NSDictionary *)launchOptions{    // Override point for customization after application launch.
 
        [application setMinimumBackgroundFetchInterval:UIApplicationBackgroundFetchIntervalMinimum];    [self.window makeKeyAndVisible];    splashView = [[UIImageView alloc]initWithFrame:CGRectMake(0, 0, 320, 568)];    [splashView setImage:[UIImage imageNamed:@"Default-568h.png"]];        return YES;}- (void)application:(UIApplication *)application performFetchWithCompletionHandler:(void (^)(UIBackgroundFetchResult))completionHandler{    NSLog(@"後臺獲取");    completionHandler(UIBackgroundFetchResultNewData);}       - (void)applicationWillResignActive:(UIApplication *)application{    // Sent when the application is about to move from active to inactive state. This can occur for certain types of temporary interruptions (such as an incoming phone call or SMS message) or when the user quits the application and it begins the transition to the background state.    // Use this method to pause ongoing tasks, disable timers, and throttle down OpenGL ES frame rates. Games should use this method to pause the game.}- (void)applicationDidEnterBackground:(UIApplication *)application{        [self.window addSubview:splashView];    [self.window bringSubviewToFront:splashView];    // Use this method to release shared resources, save user data, invalidate timers, and store enough application state information to restore your application to its current state in case it is terminated later.     // If your application supports background execution, this method is called instead of applicationWillTerminate: when the user quits.}- (void)applicationWillEnterForeground:(UIApplication *)application{    [self.splashView removeFromSuperview];    // Called as part of the transition from the background to the inactive state; here you can undo many of the changes made on entering the background.}- (void)applicationDidBecomeActive:(UIApplication *)application{    // Restart any tasks that were paused (or not yet started) while the application was inactive. If the application was previously in the background, optionally refresh the user interface.}- (void)applicationWillTerminate:(UIApplication *)application{    // Called when the application is about to terminate. Save data if appropriate. See also applicationDidEnterBackground:.}@end

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