为什么我请求 ACCESS_MEDIA_LOCATION 权限时没有显示权限框？

我正在尝试实现 Android 10 的 ACCESS_MEDIA_LOCATION 权限，以便访问照片的位置。

首先，应用程序请求 READ_EXTERNAL_STORAGE 权限，以便使用 MediaStore 访问照片。

然后应用程序使用 ExifInterface 读取照片的位置。在 Android 10 中，ExifInterface 失败，因为它没有权限。

我尝试添加 ACCESS_MEDIA_LOCATION 的权限请求，但没有出现权限请求框。然而，随后获得了许可！

如果我在获得 READ_EXTERNAL_STORAGE 权限之前先请求 ACCESS_MEDIA_LOCATION，则会出现权限请求框。

如果我随后请求 READ_EXTERNAL_STORAGE 权限，则不会出现权限请求框，但随后又会授予权限。 （我知道这样做没有意义，但我只是想看看发生了什么。）

我真的很困惑。为了访问照片的位置，应该请求用户的许可，这是有道理的，但是如果之前已授予 READ_EXTERNAL_STORAGE，为什么 ACCESS_MEDIA_LOCATION 的权限框不会出现？为什么在未经用户同意的情况下授予权限？

我是否缺少某些内容会使权限框出现？

下面的代码片段。

安卓清单：

<manifest ...>

        <uses-permission android:name="android.permission.ACCESS_FINE_LOCATION" />
        <uses-permission android:name="android.permission.ACCESS_COARSE_LOCATION" />
        <uses-permission android:name="android.permission.ACCESS_MEDIA_LOCATION" />
        <uses-permission android:name="android.permission.READ_EXTERNAL_STORAGE" />
        …

片段1：

public class Fragment1 extends Fragment {
…
        public View onCreateView(...
                …
                Log.d(TAG, "Entering Fragment1 requestPermissions operation for permission READ_EXTERNAL_STORAGE");
                Log.d(TAG, "Permission ACCESS_MEDIA_LOCATION, " + this.requireContext().checkSelfPermission(Manifest.permission.ACCESS_MEDIA_LOCATION));
                Log.d(TAG, "Permission READ_EXTERNAL_STORAGE, " + this.requireContext().checkSelfPermission(Manifest.permission.READ_EXTERNAL_STORAGE));

                String[] permission = {Manifest.permission.READ_EXTERNAL_STORAGE};
                this.requestPermissions(permission, 1);

                Log.d(TAG, "Exiting Fragment1 requestPermissions operation for permission READ_EXTERNAL_STORAGE");
                Log.d(TAG, "Permission ACCESS_MEDIA_LOCATION, " + this.requireContext().checkSelfPermission(Manifest.permission.ACCESS_MEDIA_LOCATION));
                Log.d(TAG, "Permission READ_EXTERNAL_STORAGE, " + this.requireContext().checkSelfPermission(Manifest.permission.READ_EXTERNAL_STORAGE));

                ...



        @RequiresApi(api = Build.VERSION_CODES.M)
        @Override
        public void onRequestPermissionsResult(int requestCode, String[] permissions, int[] grantResults) {
                Log.d(TAG, "Fragment1 Request Permissions callback");

                for (int i = 0; i < permissions.length; i++)
                    Log.d(TAG, "Permission " + permissions[0] + ", " + grantResults[0] );

                Log.d(TAG, "Permission ACCESS_MEDIA_LOCATION, " + this.requireContext().checkSelfPermission(Manifest.permission.ACCESS_MEDIA_LOCATION));
                Log.d(TAG, "Permission READ_EXTERNAL_STORAGE, " + this.requireContext().checkSelfPermission(Manifest.permission.READ_EXTERNAL_STORAGE));
    }

片段2：

public class Fragment2 extends Fragment {
        ...
        public View onCreate(...
                …
                Log.d(TAG, "Entering Fragment2 requestPermissions operation for permission ACCESS_MEDIA_LOCATION");
                Log.d(TAG, "Permission ACCESS_MEDIA_LOCATION, " + this.requireContext().checkSelfPermission(Manifest.permission.ACCESS_MEDIA_LOCATION));
                Log.d(TAG, "Permission READ_EXTERNAL_STORAGE, " + this.requireContext().checkSelfPermission(Manifest.permission.READ_EXTERNAL_STORAGE));

                String[] permission = {Manifest.permission.ACCESS_MEDIA_LOCATION};
                this.requestPermissions(permission, 1);     // No permission box appears here :-(

                Log.d(TAG, "Exiting Fragment2 requestPermissions operation for permission ACCESS_MEDIA_LOCATION");
                Log.d(TAG, "Permission ACCESS_MEDIA_LOCATION, " + this.requireContext().checkSelfPermission(Manifest.permission.ACCESS_MEDIA_LOCATION));
                Log.d(TAG, "Permission READ_EXTERNAL_STORAGE, " + this.requireContext().checkSelfPermission(Manifest.permission.READ_EXTERNAL_STORAGE));
                …
        
        @RequiresApi(api = Build.VERSION_CODES.M)
        @Override
        public void onRequestPermissionsResult(int requestCode, String[] permissions, int[] grantResults) {
                    Log.d(TAG, "Fragment2 Request Permissions callback");

                    for (int i = 0; i < permissions.length; i++)
                        Log.d(TAG, "Permission " + permissions[0] + ", " + grantResults[0] );

                    Log.d(TAG, "Permission ACCESS_MEDIA_LOCATION, " + this.requireContext().checkSelfPermission(Manifest.permission.ACCESS_MEDIA_LOCATION));
                    Log.d(TAG, "Permission READ_EXTERNAL_STORAGE, " + this.requireContext().checkSelfPermission(Manifest.permission.READ_EXTERNAL_STORAGE));
        }

当在 Nexus 6 API 29 模拟器上运行时，会弹出 READ_EXTERNAL_STORAGE 的第一个 UI 框，然后我点击“允许”。然后我转到第二个片段，但调用 requestPermissions 时没有弹出 UI 框。

这是日志。可以看到，当调用requestPermissions时，权限是不允许的，但是当它到达回调时，权限已经被授予：

2020-10-20 12:17:38.154 8830-8830/com.example.example1 D/ContentValues: Entering Fragment1 requestPermissions operation for permission READ_EXTERNAL_STORAGE
2020-10-20 12:17:38.155 8830-8830/com.example.example1 D/ContentValues: Permission ACCESS_MEDIA_LOCATION, -1
2020-10-20 12:17:38.155 8830-8830/com.example.example1 D/ContentValues: Permission READ_EXTERNAL_STORAGE, -1
2020-10-20 12:17:38.162 8830-8830/com.example.example1 D/ContentValues: Exiting Fragment1 requestPermissions operation for permission READ_EXTERNAL_STORAGE
2020-10-20 12:17:38.163 8830-8830/com.example.example1 D/ContentValues: Permission ACCESS_MEDIA_LOCATION, -1
2020-10-20 12:17:38.164 8830-8830/com.example.example1 D/ContentValues: Permission READ_EXTERNAL_STORAGE, -1
2020-10-20 12:17:49.544 8830-8830/com.example.example1 D/ContentValues: Fragment1 Request Permissions callback
2020-10-20 12:17:49.544 8830-8830/com.example.example1 D/ContentValues: Permission android.permission.READ_EXTERNAL_STORAGE, 0
2020-10-20 12:17:49.545 8830-8830/com.example.example1 D/ContentValues: Permission ACCESS_MEDIA_LOCATION, -1
2020-10-20 12:17:49.546 8830-8830/com.example.example1 D/ContentValues: Permission READ_EXTERNAL_STORAGE, 0
2020-10-20 12:17:55.312 8830-8830/com.example.example1 D/ContentValues: Entering Fragment2 requestPermissions operation for permission ACCESS_MEDIA_LOCATION
2020-10-20 12:17:55.313 8830-8830/com.example.example1 D/ContentValues: Permission ACCESS_MEDIA_LOCATION, -1
2020-10-20 12:17:55.318 8830-8830/com.example.example1 D/ContentValues: Permission READ_EXTERNAL_STORAGE, 0
2020-10-20 12:17:55.327 8830-8830/com.example.example1 D/ContentValues: Exiting Fragment2 requestPermissions operation for permission ACCESS_MEDIA_LOCATION
2020-10-20 12:17:55.328 8830-8830/com.example.example1 D/ContentValues: Permission ACCESS_MEDIA_LOCATION, -1
2020-10-20 12:17:55.329 8830-8830/com.example.example1 D/ContentValues: Permission READ_EXTERNAL_STORAGE, 0
2020-10-20 12:17:55.621 8830-8830/com.example.example1 D/ContentValues: Fragment2 Request Permissions callback
2020-10-20 12:17:55.622 8830-8830/com.example.example1 D/ContentValues: Permission android.permission.ACCESS_MEDIA_LOCATION, 0
2020-10-20 12:17:55.623 8830-8830/com.example.example1 D/ContentValues: Permission ACCESS_MEDIA_LOCATION, 0
2020-10-20 12:17:55.623 8830-8830/com.example.example1 D/ContentValues: Permission READ_EXTERNAL_STORAGE, 0