Android thread asynchronous message processing mechanism (i)

Android does not allow UI manipulation in child threads, but sometimes we have to perform some time-consuming tasks in the child threads and then update the corresponding UI controls based on the results of the task's execution. For this scenario, Android provides a set of asynchronous message processing mechanisms that perfectly address the problem of UI manipulation in child threads.

Main thread:

1. New Handler Object

2. Override the Parent class Handlemessage method, where the UI operation is performed, and the code for this method is in the main thread.

Child Threads:

1. Create a Message object

2. Specify what field of message

3, call handler's SendMessage method, send the message out

Examples are as follows:

Mainactivity.java:

1      PackageCom.junhao.updateui;2 3 Importandroid.app.Activity;4 ImportAndroid.os.Bundle;5 ImportAndroid.os.Handler;6 ImportAndroid.os.Message;7 ImportAndroid.view.View;8 ImportAndroid.view.View.OnClickListener;9 ImportAndroid.widget.Button;Ten ImportAndroid.widget.TextView; One  A  Public classMainactivityextendsActivityImplementsOnclicklistener { -      -      Public Static Final intUpdate_text = 1; the     PrivateTextView text; -     PrivateButton Changetext; -      -     PrivateHandler Handler =NewHandler () {//New Handler Object +          Public voidHandlemessage (Message msg) {//override the Parent class Handlemessage method, where the UI operation is performed, and the code for this method is in the main thread.  -             Switch(msg.what) { +              CaseUpdate_text: AText.settext ("Good-bye"); at                  Break; -             default: -                  Break; -             } -         } -     }; in  - @Override to     protected voidonCreate (Bundle savedinstancestate) { +         Super. OnCreate (savedinstancestate); - Setcontentview (r.layout.activity_main); the          *Text =(TextView) Findviewbyid (R.id.textview); $Changetext =(Button) Findviewbyid (r.id.changetext);Panax NotoginsengChangetext.setonclicklistener ( This); -     } the      +      Public voidOnClick (View v) { A         Switch(V.getid ()) { the          CaseR.id.changetext: +             NewThread (NewRunnable () {//Creating child Threads -                  Public voidrun () { $Message message =NewMessage ();//Create a Message object $Message.what = Update_text;//Specify what field of message -Handler.sendmessage (message);//call Handler's SendMessage method to send the message out -                 } the }). Start (); -              Break;Wuyi         default: the              Break; -         } Wu     } -}

Activity_main.xml:

1 <Relativelayoutxmlns:android= "Http://schemas.android.com/apk/res/android"2 Xmlns:tools= "Http://schemas.android.com/tools"3 Android:layout_width= "Match_parent"4 Android:layout_height= "Match_parent"5 Tools:context= "${relativepackage}.${activityclass}" >6 7     <TextView8         Android:id= "@+id/textview"9 Android:layout_width= "Wrap_content"Ten Android:layout_height= "Wrap_content" One Android:text= "@string/text"  A android:layout_centerinparent= "true"/> -      -     <Button the         Android:id= "@+id/changetext" - Android:layout_width= "Match_parent" - Android:layout_height= "Wrap_content" - Android:text= "@string/btn"/> +  - </Relativelayout>

Strings.xml:

1 <?XML version= "1.0" encoding= "Utf-8"?>2 <Resources>3 4     <stringname= "App_name">UpdateUI</string>5     <stringname= "text">How are you doing</string>6     <stringname= "BTN">Update UI</string>7 8 </Resources>

Android thread asynchronous message processing mechanism (i)