[android] Actionbar notification count icon (badge) like Google has

Edit Since version 26 of the support library (or androidx) you no longer need to implement a custom OnLongClickListener to display the tooltip. Simply call this:

TooltipCompat.setTooltipText(menu_hotlist, getString(R.string.hint_show_hot_message));

I'll just share my code in case someone wants something like this:

• layout/menu/menu_actionbar.xml

  <?xml version="1.0" encoding="utf-8"?>
  
  <menu xmlns:android="http://schemas.android.com/apk/res/android">
      ...
      <item android:id="@+id/menu_hotlist"
          android:actionLayout="@layout/action_bar_notifitcation_icon"
          android:showAsAction="always"
          android:icon="@drawable/ic_bell"
          android:title="@string/hotlist" />
      ...
  </menu>
  

• layout/action_bar_notifitcation_icon.xml

  Note style and android:clickable properties. these make the layout the size of a button and make the background gray when touched.

  <?xml version="1.0" encoding="utf-8"?>
  <RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
      android:layout_width="wrap_content"
      android:layout_height="fill_parent"
      android:orientation="vertical"
      android:gravity="center"
      android:layout_gravity="center"
      android:clickable="true"
      style="@android:style/Widget.ActionButton">
  
      <ImageView
          android:id="@+id/hotlist_bell"
          android:src="@drawable/ic_bell"
          android:layout_width="wrap_content"
          android:layout_height="wrap_content"
          android:gravity="center"
          android:layout_margin="0dp"
          android:contentDescription="bell"
          />
  
      <TextView xmlns:android="http://schemas.android.com/apk/res/android"
          android:id="@+id/hotlist_hot"
          android:layout_width="wrap_content"
          android:minWidth="17sp"
          android:textSize="12sp"
          android:textColor="#ffffffff"
          android:layout_height="wrap_content"
          android:gravity="center"
          android:text="@null"
          android:layout_alignTop="@id/hotlist_bell"
          android:layout_alignRight="@id/hotlist_bell"
          android:layout_marginRight="0dp"
          android:layout_marginTop="3dp"
          android:paddingBottom="1dp"
          android:paddingRight="4dp"
          android:paddingLeft="4dp"
          android:background="@drawable/rounded_square"/>
  </RelativeLayout>
  

• drawable-xhdpi/ic_bell.png

  A 64x64 pixel image with 10 pixel wide paddings from all sides. You are supposed to have 8 pixel wide paddings, but I find most default items being slightly smaller than that. Of course, you'll want to use different sizes for different densities.

• drawable/rounded_square.xml

  Here, #ff222222 (color #222222 with alpha #ff (fully visible)) is the background color of my Action Bar.

  <?xml version="1.0" encoding="utf-8"?>
  
  <shape
      xmlns:android="http://schemas.android.com/apk/res/android"
      android:shape="rectangle">
      <corners android:radius="2dp" />
      <solid android:color="#ffff0000" />
      <stroke android:color="#ff222222" android:width="2dp"/>
  </shape>
  

• com/ubergeek42/WeechatAndroid/WeechatActivity.java

  Here we make it clickable and updatable! I created an abstract listener that provides Toast creation on onLongClick, the code was taken from from the sources of ActionBarSherlock.

  private int hot_number = 0;
  private TextView ui_hot = null;
  
  @Override public boolean onCreateOptionsMenu(final Menu menu) {
      MenuInflater menuInflater = getSupportMenuInflater();
      menuInflater.inflate(R.menu.menu_actionbar, menu);
      final View menu_hotlist = menu.findItem(R.id.menu_hotlist).getActionView();
      ui_hot = (TextView) menu_hotlist.findViewById(R.id.hotlist_hot);
      updateHotCount(hot_number);
      new MyMenuItemStuffListener(menu_hotlist, "Show hot message") {
          @Override
          public void onClick(View v) {
              onHotlistSelected();
          }
      };
      return super.onCreateOptionsMenu(menu);
  }
  
  // call the updating code on the main thread,
  // so we can call this asynchronously
  public void updateHotCount(final int new_hot_number) {
      hot_number = new_hot_number;
      if (ui_hot == null) return;
      runOnUiThread(new Runnable() {
          @Override
          public void run() {
              if (new_hot_number == 0)
                  ui_hot.setVisibility(View.INVISIBLE);
              else {
                  ui_hot.setVisibility(View.VISIBLE);
                  ui_hot.setText(Integer.toString(new_hot_number));
              }
          }
      });
  }
  
  static abstract class MyMenuItemStuffListener implements View.OnClickListener, View.OnLongClickListener {
      private String hint;
      private View view;
  
      MyMenuItemStuffListener(View view, String hint) {
          this.view = view;
          this.hint = hint;
          view.setOnClickListener(this);
          view.setOnLongClickListener(this);
      }
  
      @Override abstract public void onClick(View v);
  
      @Override public boolean onLongClick(View v) {
          final int[] screenPos = new int[2];
          final Rect displayFrame = new Rect();
          view.getLocationOnScreen(screenPos);
          view.getWindowVisibleDisplayFrame(displayFrame);
          final Context context = view.getContext();
          final int width = view.getWidth();
          final int height = view.getHeight();
          final int midy = screenPos[1] + height / 2;
          final int screenWidth = context.getResources().getDisplayMetrics().widthPixels;
          Toast cheatSheet = Toast.makeText(context, hint, Toast.LENGTH_SHORT);
          if (midy < displayFrame.height()) {
              cheatSheet.setGravity(Gravity.TOP | Gravity.RIGHT,
                      screenWidth - screenPos[0] - width / 2, height);
          } else {
              cheatSheet.setGravity(Gravity.BOTTOM | Gravity.CENTER_HORIZONTAL, 0, height);
          }
          cheatSheet.show();
          return true;
      }
  }