Android 2.3 introduced a new developer tool called StrictMode. This tool detects disk or network operations occurring on the main thread and takes action to warn the developer.

A handler class allows you to send messages which are to be processed by the handler at some other time or immediately.

The looper class creates and manages a MessageQueue object that holds all messages for a thread.

The looper class creates and manages a MessageQueue object that holds all messages for a thread.

xhdpi is a valid screen pixel density whereas xdpi is not a valid screen pixel density.

Simple StrictMode declaration that detects all types of network and disk I/O:

StrictMode.setThreadPolicy(new StrictMode.ThreadPolicy.Builder()
 .detectAll()
 .penaltyLog()
 .penaltyDialog().build());

The method that checks for messages in the message queue can be defined as follows:

Private Boolean isTimerRunn() {
 Return mHandler.hasMessages(0);
}

In contrast to IOS devices, Android doesn’t know the size, screen resolution or aspect ratio of the devices they run on.

There are four types of screen sizes in the configuration option of android:

There are six valid Android dimension units:

dip(Density independent pixels) is an abstract unit representing a single pixel on a device with a resolution of 160 dpi but the pt(Points) unit are the 1/72 of the physical screen size.

We can extend the AsyncTask class to create a simple thread to perform background tasks and publish the results on the UI thread.

The code for recording the current system time and sending a message to the handler, starting the timer and removing any existing messages before sending the next one is as follows:

Private void startTimer() {
 mSt = System.currentTimeMillis();
 mHandler.removeMessages(0);
 mHandler.sendEmptyMessage(0);
}

AsyncTask class is useful in a situation like downloading new posts from Twitter and then loading those posts into a timeline.

Remember these points, which makes your app compatible with majority of the devices: