異步任務 (AsyncTask)

異步任務(AsyncTask)使應用程序可以適當和容易使用的UI線程. 這個類允許執行後台操作並在UI線程公佈結果, 而不必處理線程(thread)和/或處理程序(handler).



main.xml

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
   android:orientation="vertical"
   android:layout_width="fill_parent"
   android:layout_height="fill_parent"
   >
<TextView 
   android:layout_width="fill_parent"
   android:layout_height="wrap_content"
   android:text="@string/hello"
   />
<Button 
 android:id="@+id/startasynctask"
   android:layout_width="fill_parent"
   android:layout_height="wrap_content"
   android:text="Start AsyncTask" />
<Button 
 android:id="@+id/stopasynctask"
   android:layout_width="fill_parent"
   android:layout_height="wrap_content"
   android:text="Stop AsyncTask" />
<TextView 
   android:id="@+id/markingrunning"
   android:layout_width="fill_parent"
   android:layout_height="wrap_content"
   />
</LinearLayout>

java源代碼

package com.AndroidAsyncTask;

import android.app.Activity;
import android.os.AsyncTask;
import android.os.Bundle;
import android.os.SystemClock;
import android.view.View;
import android.widget.Button;
import android.widget.TextView;
import android.widget.Toast;

public class AndroidAsyncTask extends Activity {
 
 Button buttonStartAsyncTask, buttonStopAsyncTask;
 TextView tvRunningMark;
 boolean bRunning;
 
   /** Called when the activity is first created. */
   @Override
   public void onCreate(Bundle savedInstanceState) {
       super.onCreate(savedInstanceState);
       setContentView(R.layout.main);
       buttonStartAsyncTask = (Button)findViewById(R.id.startasynctask);
       buttonStopAsyncTask = (Button)findViewById(R.id.stopasynctask);
       tvRunningMark = (TextView)findViewById(R.id.markingrunning);
      
       buttonStartAsyncTask.setEnabled(true);
       buttonStopAsyncTask.setEnabled(false);
      
       buttonStartAsyncTask.setOnClickListener(new Button.OnClickListener(){

   @Override
   public void onClick(View v) {
    // TODO Auto-generated method stub
    bRunning = true;
    new RunningAsyncTask().execute();

    
   }});
      
       buttonStopAsyncTask.setOnClickListener(new Button.OnClickListener(){

   @Override
   public void onClick(View v) {
    // TODO Auto-generated method stub
    bRunning = false;
   }});

   }
  
   class RunningAsyncTask extends AsyncTask<Void, String, Void>{

    private String strRunningMark;
    
    private String rotateMarking(String marking){
     if (marking=="-"){
      return("\\"); 
     }
     else if (marking=="\\"){
      return("|"); 
     }
     else if (marking=="|"){
      return("/"); 
     }
     else{
      return("-");
      
     } 
    }

  @Override
  protected void onPostExecute(Void result) {
   // TODO Auto-generated method stub
   Toast.makeText(AndroidAsyncTask.this, "onPostExecute", Toast.LENGTH_LONG).show();
   buttonStartAsyncTask.setEnabled(true);
         buttonStopAsyncTask.setEnabled(false);
  }

  @Override
  protected void onPreExecute() {
   // TODO Auto-generated method stub
   strRunningMark = "-";
   Toast.makeText(AndroidAsyncTask.this, "onPreExecute", Toast.LENGTH_LONG).show();
   buttonStartAsyncTask.setEnabled(false);
         buttonStopAsyncTask.setEnabled(true);
  }

  @Override
  protected void onProgressUpdate(String... values) {
   // TODO Auto-generated method stub

   //tvRunningMark.setText(strRunningMark);
   tvRunningMark.setText(values[0]);
  }

  @Override
  protected Void doInBackground(Void... params) {
   // TODO Auto-generated method stub
   
   while(bRunning){
    strRunningMark = rotateMarking(strRunningMark);
    publishProgress(strRunningMark);
    SystemClock.sleep(100);
   }
   return null;
  }
    
   }
}

注意的是程序中, onPreExecute(), onPostExecute(Void result)和onProgressUpdate(String... values)都是運行在UI線程, 可以直接改變UI項目. 而doInBackground(Void... params)便在後台操作執行任務.

相關文章:
- Runnable
- 線程 (Thread)