If your application has many time-intensive operations, here are some tricks to improve the performance and provide a better experience for your users.
- Operations that can take a long time should run on their own thread and not in the main (UI) thread. If an operation takes too long while it runs on the main thread, the Android OS may show an Application not responding (ANR) dialog : from there, the user may choose to wait or to close your application. This message is not very user-friendly and your application should never have an occasion to trigger it. In particular, web services calls to an external API are especially sensitive to this and should always be on their own thread, since a network slowdown or a problem on their end can trigger an ANR, blocking the execution of your application. You can also taken advantages of threads to pre-calculate graphics that are displayed later on on the main thread.
- If your application requires a lot of call to external APIs, avoid sending the calls again and again if the wifi and cellular networks are not available. It is a waste of resources to prepare the whole request, send it off and wait for a timeout when it is sure to fail. You can pool the status of the connexion regularly, switch to an offline mode if no network is available, and reactivate it as soon as the network comes back.
- Take advantage of caching to reduce the impact of expensive operations. Calculations that are long but for which the result won’t change or graphics that will be reused can be kept in memory. You can also cache the result of calls to external APIs to a local database so you won’t depend on that resource being available at all times. A call to a local database can be faster, will not use up your users’ data plan and will work even it the device is offline. On the other hand, you should plan for a way to fresh that data from time to time, for example keeping a time and date stamp and refreshing it when it’s getting old.
- Save the current state of your activities to avoid having to recalculate it when the application is opened again. The data loaded by your activities or the result of any long-running operation should be saved when the onSaveInstanceState event is raised and restored when the onRestoreInstanceState event is raised.Since the state is saved with a serializable Bundle object, the easiest way to manage state is to have a serializable state object containing all the information needed to restore the activity so only this object needs to be saved. The information entered by the user in View controls is already saved automatically by the Android SDK and does not need to be kept in the state. Remember, the activity state may be lost when the user leaves your application or rotates the screen, not only when the user navigates to another activity.
- Make sure your layouts are as simple as possible, without unnecessary layout elements. When the view hierarchy gets too deep, the UI engine have trouble traversing all the views and calculating the position of all elements. For example, if you create a custom control and include it in another layout element, it can add an extra view that is not necessary to display the UI and that will slightly slow down the appication. You can analyse your view hierarchy to see where your layout can be flattened with the Hierarchy Viewer tool. The tool can be opened from Eclipse using the Dump View Hierarchy for UI Automator icon in the DDMS perspective, or launch the standalone tool hierarchyviewer in the <sdk>\tools\ directory.
If you have other unexplained slowdown in your application, you should profile it to help identify bottlenecks. In that case, you should take a look at my article about profiling Android applications.