崩溃原因

crash：

Assertion failure in 
-[UIApplication _runWithMainScene:transitionContext:completion:], /BuildRoot/Library/Caches/com.apple.xbs/Sources/UIKit_Sim/UIKit-

（

*** Terminating app due to uncaught exception ‘NSInternalInconsistencyException‘, `enter code here`reason: ‘Application windows are expected to have a root

view controller at the end of application launch‘

*** First throw call stack:

）

尝试解决方案一：

//  *************代码做调整，加入到下一个loop周期中，再次运行代码，程序正常。******//

- (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.

    //crash in ios9
    _testWindow = [[UIWindow alloc] initWithFrame:[UIScreen mainScreen].bounds];
    _testWindow.hidden = NO;

    //ok
    //    dispatch_async(dispatch_get_main_queue(), ^{
    //        _testWindow = [[UIWindow alloc] initWithFrame:[UIScreen mainScreen].bounds];
    //        _testWindow.hidden = NO;
    //    });

}

Or

尝试解决方案二：

　　Xcode7 需要所有的窗口都必须有根控制器

XCODE 7 requires that all the Windows must have a rootViewController You can use easy:

UIViewController* vc = [[UIViewController alloc]initWithNibName:nil bundle:nil];

 self.window.rootViewController = vc; 

It‘s working good if you need to use only UIWindow (for easy examples from any Tutorials - before Xcode 7)!