Android:检查是否在另一个类中授予了权限，而不是在MainActivity中

<uses-permission android:name="android.permission.READ_EXTERNAL_STORAGE" />

int permissionCheck = ContextCompat.checkSelfPermission(context, Manifest.permission.READ_EXTERNAL_STORAGE);

if (permissionCheck == PackageManager.PERMISSION_GRANTED) {
    // 已经授予了权限
} else {
    // 权限未被授予
}

ActivityCompat.requestPermissions(activity, new String[]{Manifest.permission.READ_EXTERNAL_STORAGE}, requestCode);

@Override
public void onRequestPermissionsResult(int requestCode, String[] permissions, int[] grantResults) {
    super.onRequestPermissionsResult(requestCode, permissions, grantResults);
    if (requestCode == requestCode) {
        if (grantResults.length > 0 && grantResults[0] == PackageManager.PERMISSION_GRANTED) {
            // 权限已被授予
        } else {
            // 权限未被授予
        }
    }
}