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content/posts/android-display-a-dialog-from-an-appwidget.md

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+template = "article.html"
+title = "Android: display a Dialog from an AppWidget"
+date = 2014-04-06T22:27:19+02:00
+description = "A workaround for displaying dialogs from Android AppWidgets, which normally can't show dialogs due to context limitations."
+
+[taxonomies]
+tags = ["android"]
++++
+
+## Issue
+
+When you want to display a dialog, you don't only need a context, you need an
+activity context. From an activity, displaying a dialog is pretty
+straightforward:
+
+*Display a dialog from an activity*
+
+```java
+new AlertDialog.Builder(MyActivity.this)
+  .setTitle("Dialog title")
+  .setMessage("Dialog message")
+  .setPositiveButton(android.R.string.yes, new DialogInterface.OnClickListener() {
+    public void onClick(DialogInterface dialog, int which) {
+      // Handle a positive answer
+    }
+  })
+  .setNegativeButton(android.R.string.no, new DialogInterface.OnClickListener() {
+    public void onClick(DialogInterface dialog, int which) {
+      // Handle a negative answer
+    }
+  })
+  .setIcon(R.drawable.ic_dialog_alert)
+  .show();
+```
+
+Okay, that's a pretty usual code sample. But what about displaying it from an
+app-widget?
+
+<!--more-->
+
+## Display a Dialog from an AppWidget
+
+What is needed to display a Dialog? An Activity. So let's open an Activity,
+which will open the Dialog. When you update your AppWidget, via a RemoteView:
+
+*Open an activity from an AppWidget*
+
+```java
+Intent intent = new Intent(getApplicationContext(), MyActivity.class);
+
+// Old activities shouldn't be in the history stack
+intent.addFlags(Intent.FLAG_ACTIVITY_NEW_TASK | Intent.FLAG_ACTIVITY_CLEAR_TASK);
+
+PendingIntent pendingIntent = PendingIntent.getActivity(getApplicationContext(),
+  0,
+  intent,
+  PendingIntent.FLAG_UPDATE_CURRENT);
+
+// Link the PendingIntent to a Button
+rv.setOnClickPendingIntent(R.id.btn_dialog, pendingIntent);
+```
+
+When the button `btn_dialog` is pressed, the activity `MyActivity` is launched.
+Let's say we have the AlertDialogBuilder code from the first sample in
+`MyActivity.onCreate()`, we have a dialog displayed from an app-widget. But there's
+an issue: we don't want the activity to be visible.
+
+## Hide the proxy activity
+
+The activity must be displayed. But what about making it fully transparent?
+That's an easy, two-steps task. First, in the manifest, remove any decoration
+and hide this activity from history:
+
+*Remove Activity decorations*
+
+```xml
+<activity
+  android:name=".activities.MyActivity"
+  android:noHistory="true"
+  android:theme="@android:style/Theme.Translucent.NoTitleBar"
+  />
+```
+
+Then in the activity itself, set a transparent background:
+
+*Set a transparent background*
+
+```java
+public class MyActivity extends Activity {
+  public void onCreate(Bundle savedInstanceState) {
+    super.onCreate(savedInstanceState);
+    getWindow().setBackgroundDrawable(new ColorDrawable(0));
+
+    // Dialog creation goes here
+  }
+}
+```
+
+At this point, there are two issues. First, if the dialog is displayed from the
+app-widget, it will appear in the recent apps list. That's probably not wanted.
+There's again a simple solution. In the manifest:
+
+*Hide the Activity from recent apps*
+
+```xml
+<activity
+  android:name=".activities.MyActivity"
+  android:noHistory="true"
+  android:excludeFromRecents="true"
+  android:theme="@android:style/Theme.Translucent.NoTitleBar"
+  />
+```
+
+The second issue is more visible. The theme `Theme.Translucent.NoTitleBar`
+refers to a pre-ICS theme, hence the Gingerbread-looking dialog.
+
+{{ img(src="/images/articles/android-display-a-dialog-from-an-appwidget/1-dialog-gb-theme.png", caption="Default theme") }}
+
+To use the Holo theme on 3.0+ devices, the dialog construction code has to be
+tweaked a little:
+
+*Applying a theme to the dialog*
+
+```java
+Context context;
+// For a custom theme:
+context = new ContextThemeWrapper(MyActivity.this, R.style.dialog);
+
+// For the Holo one on 3.0+ devices, fallback on 1.x/2.x devices:
+if (android.os.Build.VERSION.SDK_INT >= Build.VERSION_CODES.HONEYCOMB) {
+  context = new ContextThemeWrapper(MyActivity.this, android.R.style.Theme_Holo);
+} else {
+  context = new ContextThemeWrapper(MyActivity.this, android.R.style.Theme_Dialog);
+}
+
+new AlertDialog.Builder(context)
+  .setTitle("Dialog title")
+  .setMessage("Dialog message")
+  .setPositiveButton(android.R.string.yes, new DialogInterface.OnClickListener() {
+    public void onClick(DialogInterface dialog, int which) {
+      // Handle a positive answer
+    }
+  })
+  .setNegativeButton(android.R.string.no, new DialogInterface.OnClickListener() {
+    public void onClick(DialogInterface dialog, int which) {
+      // Handle a negative answer
+    }
+  })
+  .setIcon(R.drawable.ic_dialog_alert)
+  .show();
+```
+
+{{ img(src="/images/articles/android-display-a-dialog-from-an-appwidget/2-dialog-holo-theme.png", caption="Holo theme") }}
+
+If multiple dialogs are needed, the activity could be reused by adding
+parameters to the intent, and display the needed dialog accordingly. You can
+also call this activity like any other from your other activities, and share the
+dialog creation code. Here's an example of a generic dialog activity, called
+from a button on another activity:
+
+{{ img(src="/images/articles/android-display-a-dialog-from-an-appwidget/3-in-app-shared-dialog.png", caption="Dialog on top of a basic activity") }}
+
+Last point: even if the activity is invisible, it still needs to be closed when
+the dialog is hidden. Don't forget to call `Activity.finish()` when the dialogs
+are dismissed. Starting with API 17, you can use a
+`DialogInterface.OnDismissListener()`:
+
+*Finishing the activity*
+
+```java
+new AlertDialog.Builder(context)
+  .setOnDismissListener(new DialogInterface.OnDismissListener() {
+    @Override
+    public void onDismiss(DialogInterface dialogInterface) {
+      finish();
+    }
+  })
+  // …
+  .show()
+```
+
+You can find a full sample code on
+[GitHub](https://github.com/Kernald/android-dialog-activity-sample).