如何更新 LaunchScreen

由于苹果爸爸的消极支持，也由于 launch screen 本来就是 App 启动前的系统缓存行为，更换 launchScreen.storyboard 里的图片有风险，覆盖安装后可能碰到：

1. 启动画面白屏（大概是缓存更新失败）
2. 启动时看到旧的启动画面（系统缓存）

记得在 -[Application didFinishLaunch xx] 调用下面的方法（Swift 或 objc 都行）

Swift version

// 修改 LaunchScreen.storyboard 的步骤：
// 1. 图片素材改名
// 2. 不要放到 .xcassets 里面（?）
// 3. 启动时调用该方法清理缓存
// 4. 修改下面的 launchScreenVersion
// 本方法调用后下次才让新启动画面生效
func clearCacheOfLaunchScreenIfNeeded() {
    // 修改 launchScreen 时要发布的 app 版本，每次修改 LaunchScreen 都要记得修改此变量
    let launchScreenVersion = "1.9.0"
    let key = "launchScreenVersion"

    // useless
    //let appVersion = Bundle.main.infoDictionary?["CFBundleShortVersionString"] as? String

    let cachedLaunchScreenVersion = UserDefaults.standard.object(forKey: key) as? String
    let launchScreenUpdated = (cachedLaunchScreenVersion != launchScreenVersion)
    if launchScreenUpdated {
        UserDefaults.standard.set(launchScreenVersion, forKey: key)
        let home = URL(fileURLWithPath: NSHomeDirectory())
        let cacheURL = URL(fileURLWithPath: "Library/SplashBoard", relativeTo: home)
        //let cachePath = (NSHomeDirectory() as NSString).appendingPathComponent("Library/SplashBoard")
        do {
            let exists = try cacheURL.checkResourceIsReachable()
            try FileManager.default.removeItem(at: cacheURL)
            print("\(#function): \(cacheURL) exists(\(exists)) and remove successfully")
        } catch {
            print("\(#function) error: \(error)")
        }
    }
}

objc version

// 修改 LaunchScreen.storyboard 的步骤：
// 1. 图片素材改名
// 2. 不要放到 .xcassets 里面（覆盖安装后白屏问题）
// 3. 启动时调用该方法清理缓存
// 4. 修改下面的 launchScreenVersion
// 本方法调用后下次才让新启动画面生效
- (void)clearCacheOfLaunchScreenIfNeeded
{
    // 修改 launchScreen 时要发布的 app 版本
    NSString *launchScreenVersion = @"1.9.0";
    NSString *key = @"LaunchScreenVersion";
    NSUserDefaults *ud = NSUserDefaults.standardUserDefaults;
    NSString *cachedLaunchScreenVersion = [ud objectForKey:key];

    //NSString *appVersion = NSBundle.mainBundle.infoDictionary[@"CFBundleShortVersionString"];

    BOOL noRecordedCache = (cachedLaunchScreenVersion.length == 0);
    BOOL launchScreenUpdated = ([cachedLaunchScreenVersion compare:launchScreenVersion options:NSNumericSearch] != NSOrderedSame);
    if (noRecordedCache || launchScreenUpdated) {
        [ud setObject:launchScreenVersion forKey:key];

        NSString *cachePath = [NSHomeDirectory() stringByAppendingPathComponent:@"Library/SplashBoard"];
        NSURL *cacheURL = [NSURL fileURLWithPath:cachePath];

        NSError * __autoreleasing error = nil;
        if ([cacheURL checkResourceIsReachableAndReturnError:&error]) {
            error = nil;
            [NSFileManager.defaultManager removeItemAtURL:cacheURL error:&error];
            NSLog(@"%s: remove launchScreen cache error: %@", __PRETTY_FUNCTION__, error);
        } else {
            NSLog(@"%s: %@ existence checking error: %@", __PRETTY_FUNCTION__, cacheURL, error);
        }
    }
}

参考：

1. Apple news
2. human-interface-guidelines for launch-screen
3. responding to the launch of your app
4. human-interface-guidelines launch-image