Use of Handler Android

Question

Which is the better way to use a handler. Any advantages. All examples I have come across seem to give the inline version.

Using implements Handler.Callback in the class and implementing interface method.

or

Using inline code version

private Handler mHandler = new Handler(){ ....};

Answer 1

The common term or these inline class definitions is Anonymous Classes.

You can read more about the discussion on these in Java/Android: anonymous local classes vs named classes

Essentially the main differences are readbility, speed of coding, re-use and scope.

From a resource point of view the anonymous class creation may cause an overhead in the garbage collector as discussed in Avoid Creating Unnecessary Objects. I am not certain on the exact details of anonymous class creation, however, it is logical that implementing the interface on the class is more efficient.

@WilliamTMallard has provided an example of what NOT to do. In his example, a long and syntacticly complex handler should be implementented on the class rather than anonymous handler because it is harder to read and edit when defined inline.

Answer 2

http://developer.android.com/reference/android/os/Handler.html

package : android.os
public class
Handler
extends Object

A Handler allows you to send and process Message and Runnable objects associated with a thread's MessageQueue. Each Handler instance is associated with a single thread and that thread's message queue. When you create a new Handler, it is bound to the thread / message queue of the thread that is creating it -- from that point on, it will deliver messages and runnables to that message queue and execute them as they come out of the message queue.

There are two main uses for a Handler:

1. to schedule messages and runnables to be executed as some point in the future; and
2. to enqueue an action to be performed on a different thread than your own.

Exmaple 1

use handler in app splash page.

if (!isFirstIn) {
    mHandler.sendEmptyMessageDelayed(GO_HOME, SPLASH_DELAY_MILLIS);
} else {
    mHandler.sendEmptyMessageDelayed(GO_GUIDE, SPLASH_DELAY_MILLIS);
} 


/**************************************************************************************
*1. Handler
*/
private Handler mHandler = new Handler() {
    public void handleMessage(Message msg) {
        if(isAuto){
            switch (msg.what) {
            case GO_HOME:
                goHome();
                break;
            case GO_GUIDE:
                goGuide();
                break;
            }
        }
        super.handleMessage(msg);
    }
}; 
private void goHome() {
    Intent intent = new Intent(SplashActivity.this, MainAct.class);
    SplashActivity.this.startActivity(intent);
    SplashActivity.this.finish();
} 

private void goGuide() {
    Intent intent = new Intent(SplashActivity.this, GuideActivity.class);
    SplashActivity.this.startActivity(intent);
    SplashActivity.this.finish();
} 

Example 2

use Handler request network in child thread if the request work may takes time.

new Thread(new Runnable(){
    @Override
    public void run() {
        String versionPath = Parameters.getCheckVersionPath();
        String result = RequestHelper.doGet(versionPath, null);
        Message msg = new Message();
        Bundle data = new Bundle();
        data.putString("result",result);
        msg.setData(data);
        handler1.sendMessage(msg);
    }
}).start();

handler1 = new Handler(){
    @Override
    public void handleMessage(Message msg) {
        String result = msg.getData().getString("result");
        JSONObject obj;
        try {
            obj = new JSONObject(result);
            Map<String, String> versionInfo = Helper.getSoftwareVersion(obj);
            if (versionInfo != null) {
                newVersion = versionInfo.get("version");
                updateUrl = versionInfo.get("url");
            }
        } catch (JSONException e) {
            Log.w("net work error!", e);
        }
    }

}; 

Example 3

use Handler and Timer to update progress bar.

logobar = (ImageView) findViewById(R.id.splash_bar);//progress bar.
logobarClipe = (ClipDrawable) logobar.getBackground();

timer = new Timer();
timer.schedule(new TimerTask() {
    public void run() {
        updateLogoBarHandler.sendEmptyMessage(0);
}}, 0, rate);


/**************************************************************************************
*2. Handler
*/
//update progress bar.
private Handler updateLogoBarHandler = new Handler() {
    public void handleMessage(Message msg) {
        if(logobarClipe.getLevel() < 10000){
            //1.update image.
            logobarClipe.setLevel(logobarClipe.getLevel() + rate*2);  

            //2.update text.
            float percent = logobarClipe.getLevel() /100;
            String percentTxtVerbose = String.valueOf(percent);
            String percentTxt = percentTxtVerbose.substring(0, percentTxtVerbose.indexOf('.')) + "%";
            bartxt.setText(percentTxt);

        }else{
            timer.cancel();
        }  
        super.handleMessage(msg);
    }
};