refactored permission handling to separate class

src/com/owncloud/android/ui/activity/FileDisplayActivity.java

@@ -100,6 +100,7 @@ import com.owncloud.android.ui.preview.PreviewVideoActivity;
 import com.owncloud.android.utils.DisplayUtils;
 import com.owncloud.android.utils.ErrorMessageAdapter;
 import com.owncloud.android.utils.FileStorageUtils;
+import com.owncloud.android.utils.PermissionUtil;
 import com.owncloud.android.utils.UriUtils;
 
 import java.io.File;
@@ -112,7 +113,6 @@ public class FileDisplayActivity extends HookActivity
         implements FileFragment.ContainerActivity,
         OnSslUntrustedCertListener, OnEnforceableRefreshListener {
 
-    private static final int PERMISSIONS_WRITE_EXTERNAL_STORAGE = 1;
     private SyncBroadcastReceiver mSyncBroadcastReceiver;
     private UploadFinishReceiver mUploadFinishReceiver;
     private DownloadFinishReceiver mDownloadFinishReceiver;
@@ -210,33 +210,26 @@ public class FileDisplayActivity extends HookActivity
     protected void onPostCreate(Bundle savedInstanceState) {
         super.onPostCreate(savedInstanceState);
 
-        if (ContextCompat.checkSelfPermission(this, Manifest.permission.WRITE_EXTERNAL_STORAGE)
-                != android.content.pm.PackageManager.PERMISSION_GRANTED) {
+        if (PermissionUtil.checkSelfPermission(this, Manifest.permission.WRITE_EXTERNAL_STORAGE)) {
             // Check if we should show an explanation
-            if (ActivityCompat.shouldShowRequestPermissionRationale(this,
+            if (PermissionUtil.shouldShowRequestPermissionRationale(this,
                     Manifest.permission.WRITE_EXTERNAL_STORAGE)) {
-
-                // write access isn't considered a rationale enforced permission in 23
-                // code is still in place in case this changes in the future
-
                 // Show explanation to the user and then request permission
                 Snackbar snackbar = Snackbar.make(findViewById(R.id.ListLayout), R.string.permission_storage_access,
                         Snackbar.LENGTH_INDEFINITE)
                         .setAction(R.string.common_ok, new View.OnClickListener() {
                             @Override
                             public void onClick(View v) {
-                                requestWriteExternalStoreagePermission();
+                                PermissionUtil.requestWriteExternalStoreagePermission(FileDisplayActivity.this);
                             }
                         });
 
-                // Changing action button text color
-                View sbView = snackbar.getView();
-                TextView textView = (TextView) sbView.findViewById(android.support.design.R.id.snackbar_action);
-                textView.setTextColor(ContextCompat.getColor(this, R.color.white));
+                DisplayUtils.colorSnackbar(this, snackbar);
+
                 snackbar.show();
             } else {
                 // No explanation needed, request the permission.
-                requestWriteExternalStoreagePermission();
+                PermissionUtil.requestWriteExternalStoreagePermission(this);
             }
         }
 
@@ -250,20 +243,11 @@ public class FileDisplayActivity extends HookActivity
         setBackgroundText();
     }
 
-    /**
-     * request the write permission for external storage.
-     */
-    private void requestWriteExternalStoreagePermission() {
-        ActivityCompat.requestPermissions(this,
-                new String[]{Manifest.permission.WRITE_EXTERNAL_STORAGE},
-                PERMISSIONS_WRITE_EXTERNAL_STORAGE);
-    }
-
     @Override
     public void onRequestPermissionsResult(int requestCode,
                                            String permissions[], int[] grantResults) {
         switch (requestCode) {
-            case PERMISSIONS_WRITE_EXTERNAL_STORAGE: {
+            case PermissionUtil.PERMISSIONS_WRITE_EXTERNAL_STORAGE: {
                 // If request is cancelled, result arrays are empty.
                 if (grantResults.length > 0
                         && grantResults[0] == PackageManager.PERMISSION_GRANTED) {

src/com/owncloud/android/utils/DisplayUtils.java

@@ -28,10 +28,14 @@ import android.content.Context;
 import android.graphics.Point;
 import android.graphics.PorterDuff;
 import android.os.Build;
+import android.support.design.widget.Snackbar;
+import android.support.v4.content.ContextCompat;
 import android.text.format.DateUtils;
 import android.view.Display;
+import android.view.View;
 import android.widget.ProgressBar;
 import android.widget.SeekBar;
+import android.widget.TextView;
 
 import com.owncloud.android.MainApp;
 import com.owncloud.android.R;
@@ -278,4 +282,16 @@ public class DisplayUtils {
         }
     }
 
+    /**
+     * set the owncloud standard colors for the snackbar.
+     *
+     * @param context the context relevant for setting the color according to the context's theme
+     * @param snackbar the snackbar to be colored
+     */
+    public static void colorSnackbar(Context context, Snackbar snackbar) {
+        // Changing action button text color
+        View sbView = snackbar.getView();
+        TextView textView = (TextView) sbView.findViewById(android.support.design.R.id.snackbar_action);
+        textView.setTextColor(ContextCompat.getColor(context, R.color.white));
+    }
 }

src/com/owncloud/android/utils/PermissionUtil.java

@@ -0,0 +1,53 @@
+package com.owncloud.android.utils;
+
+import android.Manifest;
+import android.app.Activity;
+import android.content.Context;
+import android.support.v4.app.ActivityCompat;
+import android.support.v4.content.ContextCompat;
+
+/**
+ * Created by scherzia on 29.12.2015.
+ */
+public class PermissionUtil {
+    public static final int PERMISSIONS_WRITE_EXTERNAL_STORAGE = 1;
+
+    /**
+     * Wrapper method for ContextCompat.checkSelfPermission().
+     * Determine whether <em>the app</em> has been granted a particular permission.
+     *
+     * @param permission The name of the permission being checked.
+     *
+     * @return <code>true</code> if app has the permission, or <code>false</code> if not.
+     */
+    public static boolean checkSelfPermission(Context context, String permission) {
+        return ContextCompat.checkSelfPermission(context, permission)
+                != android.content.pm.PackageManager.PERMISSION_GRANTED;
+    }
+
+    /**
+     * Wrapper method for ActivityCompat.shouldShowRequestPermissionRationale().
+     * Gets whether you should show UI with rationale for requesting a permission.
+     * You should do this only if you do not have the permission and the context in
+     * which the permission is requested does not clearly communicate to the user
+     * what would be the benefit from granting this permission.
+     *
+     * @param activity The target activity.
+     * @param permission A permission to be requested.
+     * @return Whether to show permission rationale UI.
+     */
+    public static boolean shouldShowRequestPermissionRationale(Activity activity, String permission) {
+        return ActivityCompat.shouldShowRequestPermissionRationale(activity, permission);
+    }
+
+    /**
+     * request the write permission for external storage.
+     *
+     * @param activity The target activity.
+     */
+    public static void requestWriteExternalStoreagePermission(Activity activity) {
+        ActivityCompat.requestPermissions(activity,
+                new String[]{Manifest.permission.WRITE_EXTERNAL_STORAGE},
+                PERMISSIONS_WRITE_EXTERNAL_STORAGE);
+    }
+}