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Friday, October 29, 2010

Experience - Android Drag and Drop List

I am continually surprised by the fact that the things I need for my application do not exist in android. This time I needed a drag and drop list. I have been unsuccessful in finding a simple, working drag and drop list that I can extend. I have seen numerous places that reference android's music app as a starting place. The main classes of importance from the music app were TouchInterceptor and TrackBrowserActivity. Many of the examples that I have seen struggled to use it well and most ended up having serious problems as a result. I would rate the TouchInterceptor code with a rating of "F" because it is not simple and it is not easily extendable. Check out this article for a way to rate code. It left a good impression on me.

This experience is about my efforts to build a simplified drag and drop list. I hope time will prove that it is easy to extend as well. The first task was to get a copy of TouchInterceptor and TrackBrowserActivity running in a simplified project. This took time because of all the dependencies and interconnections between these two classes and the rest of the app. As I look back on the matter the only real benefit this provided me with was a better understanding of how not to make TouchInterceptor work. After I had a runnable project, I attempted to modify the drag animation from an expanding/contracting items on drag to one that rearranged items in place. I was almost finished with this change when I ran into a technical issue that I didn't want to spend time to fix. I then discovered that the Launcher app provided a better drag and drop example because it was simplified compared to some of the complex interactions in the music app. Using both the music app and the launcher app as a reference I wrote a simplified drag and drop project. You can find the project here.

I wanted to provide methods that allowed modifying/customizing the view of the item being dragged, but not fall into the same complex interactions of the music app. I chose to use the DragListener with the intended purpose of handling view changes. In the sample project, I made the item's view invisible to show where the drag view came from, and I changed the background color to show that a drag view is different from the rest of the item views. It is important to revert any changes to the item view because it will be recycled back into the list view for item views.

This project code is simply to share a simple working drag and drop list since I was unable to find one elsewhere on the web. If you add any extensions to this simple project I would like to hear about it in the comments.

Wednesday, October 13, 2010

Experience - Customizing Android's Tab Indicator

I was displeased by the initial look-n-feel of the Tabs on my TabActivity. When I ran the app on the emulator the non-selected tabs had a nice gray background and the selected tab was white. No issue here, but when I ran the exact same app on my device all the backgrounds were white as well as the text on each tab. This was a horrible combination it was nearly impossible to see any part of the Tabs. A description that I like of this problem can be found here.

Below I have listed several ways that I tried to fix the problem as well as the final solution that I decided on.

1) Customize theme & xml for Tab.
I started off looking for a way to customize the xml on TabWidget, TabHost, and even TabHost.Tabspec. I found out that TabHost didn't have much. TabWidget looked promising as I could change the look-n-feel of the divider and the bottom strip. Two nice features but what about the tab indicator? I then looked at TabHost.TabSpec this seemed to be the most promising but I found no xml attributes to change. Still wanting to change the look with xml I started digging into the theme looking for a way to change the look of a tab indicator. I was operating under the impression that this was just a theme problem and I thought a simple customization to the theme and all TabWidgets would display properly. The best resource I found can be found here, however this did not solve my problem.

2) Accessing TabWidget's children in code.
The second approach I took after a quick Google search was to try Advance Tab's idea. I was able to successfully change the tab indicators in code using a line similar to the following:

final TextView tv = (TextView) tabWidget.getChildAt(i).findViewById(;


Changing the look through code is less than ideal and calling TabWidget's getChildAt() method was definitely not how the designers intended to change the tab indicator. I was very happy to have made some progress. However, I still wanted to be able to change the look in xml, so this approach didn't really solve my problem either.

3) Building a view for Tab's Indicator.
After several attempts and time spent on things that produced less than desirable results, I realized I had overlooked something simple. The "ah ha" moment (as I like to call it) came when I took another look at the TabHost.TabSpec's setIndicator() method. Since API level 4 we have been able to create a view and set it as the tab indicator. I felt like this way was simplistic and easy.

Below is a quick overview of how I configured my tab indicator view.
I created a tabindicator.xml like the following:

<?xml version="1.0" encoding="utf-8"?>

<RelativeLayout xmlns:android=""
android:layout_width="fill_parent" android:layout_height="fill_parent">

<TextView android:id="@+id/title"
android:layout_below="@id/title" android:layout_width="wrap_content"
android:layout_centerInParent="true" android:text="Title">
<ImageView android:id="@+id/icon"

The code in my TabActivity looks like this:

public void onCreate(Bundle savedInstanceState) {

View indicator1 = getLayoutInflater().inflate(R.layout.tabindicator, null);
TextView title1 = (TextView)indicator1.findViewById(;

TabHost tabHost = getTabHost();
.setContent(new Intent(this, TabGroup1Activity.class)));

I have left out some details, but hopefully this gives the basic idea on how I built my own tab indicator view. Good luck!