Examples

Android / Developer / Examples — Comments Off
19
Oct 11

Unexpected Behavior when working with Nested TabHosts

During my last project I’ve encountered two problems which caused my app to crash which I did not expect to happen because the exact same code was working within other activities. These crashes were triggered by simple things like a press on the search button of the mobile phone or the creation of a dialog. When analyzing this behavior I’ve identified a nested TabHost View (a TabHost containing another TabHost which contains the Activity) as the cause for the crashes.

One TabHost contains another TabHost. The last TabHost contains the actual content.The problematic setup is shown in the picture to the left. As you can see the outer TabHost contains a Tab which Activity itself is the inner TabHost. The content of this TabHost will be placed between both tabs. So this is a design which doesn’t seem to be so out of the world.

In the following I’m going to point out the two problems and the solutions which I’ve found so that you might be able to solve similar problems. To demonstrate the problems I’ve created an example project which causes the errors and one which contains the proposed solutions where the functions are working. Continue reading →

Android / Animation / API / Developer / Examples — 4 Comments
27
May 11

Playing Animations in Android

If you want to add an animation to your app the first thing you think about is to use animated gifs. But when you perform some research on how to use animated gifs in android you will find out that android does not support this file type. Instead android will always just display one static frame of the animation. But android provides two powerful mechanisms which allow developers to create various types of animations. One way is to use tweened animations where you can define transformation operations such as acceleration, alpha, rotation, scaling, position, etc.  on your objects. The other possibility is to use a frame-by-frame mechanism where it’s possible to define different drawable resources and time intervals in which these resources will be displayed. In this blog post I want to give an introduction on how this frame by frame animation can be implemented in android.
Continue reading →

AIDL / Android / API / Examples / Interprocess Communication — 1 Comment
13
May 11

Using self-defined Parcelable objects during an Android AIDL RPC / IPC call

In my previous post “Using the Android Interface Definition Language (AIDL) to make a Remote Procedure Call (RPC) in Android” I’ve explained the basics on how inter-process communication can be implemented in Android. Now we will take a look at a specialized field in this area: Using Parcelables as parameters of an AIDL method.
As described in the previous post it is possible to either use primitive java types within a remote method signature or any class which implements the android.os.Parcelable interface. Using this interface it is possible to define arbitrarily complex data types which can be used as parameters or return values of methods during a remote method call.
I’ve created a modified version of the first example app to give you a basic example which relies on a Parcelable object as a method return value. Continue reading →

AIDL / Android / API / Examples / Interprocess Communication — 11 Comments
26
Apr 11

Using the Android Interface Definition Language (AIDL) to make a Remote Procedure Call (RPC) in Android

There are different ways to communicate with a Service. A commonly used approach is to use Intents where the Service can respond according to the intent action. This is easily implemented but if the Service is providing many different operations the resulting code might become complex which will result in a hardly maintainable code. Furthermore, when using Intents the developer always has to take care of adding the parameters to the intent and after the result intent was received the result-parameters have to be retrieved from the intent. This will result in an increased programming overhead within the client each time a remote functionality is called which can lead to error-prone code. To avoid these disadvantages you can use the built-in Remote Procedure Call (RPC) mechanism of Android. To demonstrate the use of RPCs in Android I’ve created a basic example. This example consists of two apps where the first contains a Service and the second an Activity. The Activity will connect to the Service using the Android RPC mechanism and will query a String from that Service. Continue reading →

Android / API / Examples / Resources — Comments Off
13
Apr 11

Using Android Activities and Services in multiple Projects

When developing Apps for the Android OS you might end up in the situation where you have common Activities or Services which could be reused in multiple Apps with just a little modification. As you don’t want to copy these classes into every single project – which would lead to a hardly maintainable code – you would seek a way to reference the source of these classes from multiple projects. For non-android applications an approach for this problem would be to break up the code into multiple libraries so that the required functionality can be referenced from multiple projects. As long as you are not interacting with external resources this attempt is also possible in Android projects (build a jar and reference it from the projects). But if you are using external resources these classes can’t be used within a library. This is caused by the fact that the Android SDK won’t generate matching ids within the “R” class for external resources which are included in a referenced jar file. In this post I want to show you different solutions for this problem which can avoid the necessity to copy the source code into the projects. Continue reading →