最近发现一个问题，我在使用ContextCompat.CheckSelfPermission()时无论如何开关权限返回值都是PackageManager.PERMISSION_GRANTED，而使用PackageManager.checkPermission()的时候返回值又始终都是PackageManager.PERMISSION_DENIED;
经过多番尝试和查找资料发现原因：
If your application is targeting an API level before 23 (Android M) then both:ContextCompat.CheckSelfPermission and Context.checkSelfPermission doesn't work and always returns 0 (PERMISSION_GRANTED). Even if you run the application on Android 6.0 (API 23).
在targetSdkVersion小于23(Android M)的时候，ContextCompat.CheckSelfPermission 和Context.checkSelfPermission方法都不能正常工作并且始终返0(PERMISSION_GRANTED)，即使你的应用运行在Android6.0(API 23)的设备上。
解决办法：
As I said in the 1st point, if you targeting an API level before 23 on Android 6.0 then ContextCompat.CheckSelfPermission and Context.checkSelfPermission doesn't work. Fortunately you can use PermissionChecker.checkSelfPermission to check run-time permissions.
可以使用PermissionChecker.checkSelfPermission()去检查权限是否被授予。
转自：https://www.jianshu.com/p/2a452546cc1f