In this Android tip, I am going to give you an example of using AsyncTask class to extract a zip file. AsyncTask is a useful generic class in Android. It can be used to perform a long-run task in background progress. Typically, there three methods of the AsyncTask class, you have to override. They are onPreExecute, doInBackground, and onPostExecute methods. In the onPreExecute method, you can write code to do something before the long-run task starts. In this AsyncTask example, code is written to show a progress dialog. In the doInBackground method, you will place the code to perform the long-run task. In this example, extracting a zip file is the long-run task that is placed in the doInBackground method. In the onPostExecute method, you can write code to do something after the long-run task finishes. In this example, code is written to close the progress dialog.

<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
     xmlns:tools="http://schemas.android.com/tools"
     android:id="@+id/container"
     android:layout_width="match_parent"
     android:layout_height="match_parent"
     android:orientation="vertical"
     android:paddingBottom="@dimen/activity_vertical_margin"
     android:paddingLeft="@dimen/activity_horizontal_margin"
     android:paddingRight="@dimen/activity_horizontal_margin"
     android:paddingTop="@dimen/activity_vertical_margin"
     tools:context=".MainActivity"
      
      >
    <EditText
        
  		android:id="@+id/txt_filepath"
  		android:layout_width="fill_parent"
  		android:layout_height="wrap_content"
  		android:hint="Enter zip file path" 		
  				
  	/>
    <Button
       android:id="@+id/bt_ok"
       android:layout_width="wrap_content"
  	  android:layout_height="wrap_content"
  	  android:text="Extract"
  	  android:onClick="startExtract"
       
       />
  
  </LinearLayout>

  package com.example.andtip;
  
  import java.io.File;
  import java.io.FileOutputStream;
  import java.io.IOException;
  import java.io.InputStream;
  import java.util.Enumeration;
  import java.util.zip.ZipEntry;
  import java.util.zip.ZipFile;
  import android.app.Activity;
  import android.app.PendingIntent;
  import android.app.ProgressDialog;
  import android.os.Bundle;
  import android.os.Environment;
  import android.view.View;
  import android.widget.TextView;
  import android.widget.Toast;
  import android.os.AsyncTask;
  public class MainActivity extends Activity{
  	Activity context;
     
   	protected void onCreate(Bundle savedInstanceState) {
     	//TODO Auto-generated method stub
     	super.onCreate(savedInstanceState);
     	setContentView(R.layout.activity_main);
     	context=this;
     	
     	
     }
   public void startExtract(View view){
   	BackTask bt=new BackTask();
   	TextView tv=(TextView)findViewById(R.id.txt_filepath);
   	String filepath=tv.getText().toString();
   	String despath=Environment.getExternalStorageDirectory()+"/myfiles";
   	if(filepath.trim().length()>0)
   	{
   		bt.execute(new String[]{filepath,despath});
   	}
   	else{
   		Toast.makeText(context, "Empty file path", Toast.LENGTH_SHORT).show();
   	}
   }
   	//background process to extract a zip file
     private class BackTask extends AsyncTask<String,Void,Void>{  
       protected void onPreExecute(){
       	 super.onPreExecute();
       	 //display progress dialog
       	 pd = new ProgressDialog(context);
       	 pd.setTitle("Extracting the text file");
       	 pd.setMessage("Please wait.");
       	 pd.setCancelable(true);
       	 pd.setIndeterminate(false);
       	 pd.show(); 
       	
       	}
     
       	protected Void doInBackground(String...params){ 
       	  
       		extractFile(params[0],params[1]);
  
       	   return null;
       	
       	}    
       	
       	
       	protected void onPostExecute(Void result){
       		//close dialog
       		if(pd!=null)
       			pd.dismiss();  	
       		
       	
       	}     	
      
       	
       }   
     public void extractFile(String srcfile, String despath){
  		ZipFile zf=null;
     	try {
  			zf=new ZipFile(srcfile); //create  a zip file object
  			if(zf.size()>0){ //read through the zip file
  				Enumeration<ZipEntry> entries=(Enumeration<ZipEntry>) zf.entries();
  				while(entries.hasMoreElements()){
  					ZipEntry entry=entries.nextElement();
  					if(!entry.isDirectory() && !entry.getName().endsWith("/")){
  						//start extracting the files
  						extract(zf.getInputStream(entry),entry.getName(),despath);
  						
  					}
  					
  				}
  				
  			}
  			
  				
  		} catch (IOException e) {
  			if(pd!=null) pd.isShowing();			
  			e.printStackTrace();
  			
  		}finally{
  				if(zf!=null)
  				try {
  					zf.close();
  				} catch (IOException e) {
  					// TODO Auto-generated catch block
  					e.printStackTrace();
  				}
  			
  		}
    	 }
     
  public void extract(InputStream is, String fname, String storeDir){
  		
  		FileOutputStream fos;		
  		File fi=new File(storeDir+File.separator+fname); //output file
  		File fparent=new File(fi.getParent());
  		fparent.mkdirs();//create parent directories for output files
  		
  		try {
  			
  			fos=new FileOutputStream(fi);
  			int content=0;			
  			while((content=is.read())!=-1){
  				fos.write(content);
  			}
  			is.close();
  			fos.close();
  		} catch (Exception e) {
  			
  			e.printStackTrace();
  		}
  		
  	}
  }
  

Posted by: Dara | post date: 08-02-2014 | Subject: Android Apps Development