(Android review) basic use of handler, androidhandler

(Android review) basic use of handler, androidhandler

I. Basic knowledge points

1. Intent intent = new Intent (); // open the browser's
Intent. setAction (Intent. ACTION_VIEW );
Intent. setData (Uri. parse ("http://www.baidu.com "));


2. SystemClock. sleep (20000); // sleep for 20 seconds to hide the game


3. Time-consuming operations should be performed in sub-threads
Obtain data online
Copying large files
Must be placed in the sub-thread for operation.


The onCreate () button clicks the callback event and the displayed operations are all run in the main thread. UI thread.


4. handler usage
New Handler ();


Message msg = new Message ();
Msg. what = UPDATE_DISPLAY; // sets unique message recognition.
Msg. obj = I;
MHandler. sendMessage (msg)

Ii. Sample Code

package com.example.handlertest;import android.os.Bundle;import android.os.Handler;import android.os.Message;import android.os.SystemClock;import android.app.Activity;import android.view.Menu;import android.view.View;import android.widget.TextView;public class MainActivity extends Activity {public TextView tv_num;public static final int UPDATE_NUMBER = 0;public int i = 0;public Handler handler = new Handler(){public void handleMessage(android.os.Message msg) {if(msg.what == UPDATE_NUMBER){int i = (Integer) msg.obj;tv_num.setText(i + "");}};};@Overrideprotected void onCreate(Bundle savedInstanceState) {super.onCreate(savedInstanceState);setContentView(R.layout.main);tv_num = (TextView) findViewById(R.id.tv_number);}public void add(View view){new Thread(){@Overridepublic void run() {super.run();while(i < 100){SystemClock.sleep(1000);i += 1;Message msg = new Message();msg.what = UPDATE_NUMBER;msg.obj = i;handler.sendMessage(msg);}}}.start();}@Overridepublic boolean onCreateOptionsMenu(Menu menu) {// Inflate the menu; this adds items to the action bar if it is present.getMenuInflater().inflate(R.menu.main, menu);return true;}}

3. Download source code

Http://download.csdn.net/detail/caihongshijie6/7798627

IV,

How to Use Handler in Android

You can directly create your own thread to complete some work.
Handler is mainly used to interact with the main UI thread. For example:
1. You use handler to send a message, and then receive and process the message in the handler thread to avoid affecting other processing tasks of the UI main thread by directly processing transactions in the UI main thread.
2. You can pass the handler object to other processes to send events to you through handler in other processes.
3. You can use handler to send messages in a delayed manner to process some transactions.

Handler usage in android

I am also using Handler, which is used to simulate the example. It is mainly used to send messages to the main program by sub-threads for Handler object processing. I also have your questions. This new Handler () {} is just an instant, but it still monitors its own messages for processing at any time, this seems to be a bit unconventional, but I think it's like a button control object,
Click it to respond to a click event.