Pivotal Android Tabs

We have published a simple Android project that illustrates how to use tabs in an Android app: TabActivity, TabHost, TabWidget, and android:divider. Thank you Pivot Ryan, the original author, for taking the time to write and open source this. Check it out, fork it, and enjoy — https://github.com/pivotal/Pivotal-Android-Tabs

See Hex’d Colors

IntelliJ trick: in a colors.xml file, place your cursor on a hex value and hold down Shift. You’ll see a large preview of the color.

Colors and States

(Repost from the 6/22/2011 Standup blog): You can use a selector drawable to set Android text color for the various states (focused, selected, etc.) using a drawable xml file. IntelliJ will complain and say this is invalid syntax but the application will use the file as you would expect. This only seems to work for the android:textColor attribute in TextViews.

Android ListView#addHeaderView and ListView#addFooterView methods are strange: you have to add the header and footer Views before you set the ListView‘s adapter so the ListView can take the headers and footers into consideration — you get an exception otherwise. Here we add a ProgressBar (spinner) as the headerView:

// spinner is a ProgressBar
listView.addHeaderView(spinner);

We’d like to be able to show and hide that spinner at will, but removing it outright is dangerous because we’d never be able to add it again without destroying the ListView — remember, we can’t addHeaderView after we’ve it’s adapter:

listView.removeHeaderView(spinner); //dangerous!

So let’s hide it! Turns out that’s hard, too. Just hiding the spinner view itself results in an empty, but still visible, header area.

Now try to hide the spinner:

spinner.setVisibility(View.GONE);

Result: header area still visible with an ugly space:

The solution is to put the progress bar in a LinearLayout that wraps it’s content, and hiding the content. That way the wrapping LinearLayout will collapse when its content is hidden, resulting in a headerView that is technically still present, but 0dip high:

  <LinearLayout
      xmlns:a="http://schemas.android.com/apk/res/android"
      android:orientation="vertical"
      android:layout_width="fill_parent"
      android:layout_height="wrap_content">
    <!-- simplified -->
      <ProgressBar
        android:id="@+id/spinner"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"/>
  </LinearLayout>

Then, set the layout as the header:

spinnerLayout = getLayoutInflater().inflate(R.layout.header_view_spinner, null);
listView.addHeaderView(spinnerLayout);

And when we need to hide it, hide the layout’s content, not the layout:

    spinnerLayout.findViewById(R.id.spinner).setVisibility(View.GONE);

Now the header disappears from view. No more ugly space at the top!