Clear “Cache” onDestroy

Question

What I try to do

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I'm building a application for my Channel. I get the data over the JSON from google and fill that into my ListView over the SimpleAdapter.

That I can show the pictures in my SimpleAdapter, i save them onto my SDCard. The Problem is now, when the app gets killed I get a forceclose error because the pictures are allready there.

Question

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How can I delte the "Cached" images on my SDCard on onDestroy()?

Down here you find the Code of the app. Thank you for your help in advance!

Code

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ChannelActivity.java

package de.stepforward;

import java.io.BufferedInputStream;
import java.io.BufferedReader;
import java.io.File;
import java.io.FileOutputStream;
import java.io.IOException;
import java.io.InputStream;
import java.io.InputStreamReader;
import java.net.URI;
import java.net.URL;
import java.net.URLConnection;
import java.util.ArrayList;
import java.util.HashMap;
import java.util.Map;


import org.apache.http.util.ByteArrayBuffer;
import org.json.JSONArray;
import org.json.JSONObject;

import de.stepforward.web.ShowVideo;


import android.app.ListActivity;
import android.content.Intent;
import android.graphics.Bitmap;
import android.graphics.BitmapFactory;
import android.graphics.drawable.BitmapDrawable;
import android.graphics.drawable.Drawable;
import android.os.Bundle;
import android.os.Environment;
import android.util.Log;
import android.view.View;
import android.widget.AdapterView.OnItemClickListener;
import android.widget.AdapterView;
import android.widget.ImageView;
import android.widget.ListAdapter;
import android.widget.ListView;
import android.widget.SimpleAdapter;



public class ChannelActivity extends ListActivity {


    @Override
    public void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.main);

    //Cache löschen wenn Applikation gekillt wird


    String result = "";
    String line = null;
    final ArrayList<HashMap<String, Object>> mylist = new ArrayList<HashMap<String, Object>>();


    //get the Data from URL
    try{
    URL url = new URL("http://gdata.youtube.com/feeds/mobile/users/TheStepForward/uploads?alt=json&format=1"); 

    URLConnection conn = url.openConnection();
    StringBuilder sb = new StringBuilder();
    BufferedReader rd = new BufferedReader(new InputStreamReader(conn.getInputStream()));

    //read d response till d end
    while ((line = rd.readLine()) != null) {
    sb.append(line + "\n");
    }
    result = sb.toString();
    Log.v("log_tag", "Append String " + result);
    } catch (Exception e) {
    Log.e("log_tag", "Error converting result " + e.toString());
    }

    try{
        JSONObject json = new JSONObject(result);
        JSONObject feed = json.getJSONObject("feed");
        JSONArray entrylist = feed.getJSONArray("entry");

        for(int i=0;i<entrylist.length();i++){
            //Get Title
            JSONObject movie = entrylist.getJSONObject(i);
            JSONObject title = movie.getJSONObject("title");
            String txtTitle = title.getString("$t");
            Log.d("Title", txtTitle);

            //Get Description
            JSONObject content = movie.getJSONObject("content");
            String txtContent = content.getString("$t");
            Log.d("Content", txtContent);

            //Get Link
            JSONArray linklist = movie.getJSONArray("link");
            JSONObject link = linklist.getJSONObject(0);
            String txtLink = link.getString("href");
            Log.d("Link", txtLink);


            //Get Thumbnail
            JSONObject medialist = movie.getJSONObject("media$group");
            JSONArray thumblist = medialist.getJSONArray("media$thumbnail");
            JSONObject thumb = thumblist.getJSONObject(2);
            String txtThumb = thumb.getString("url");
            Log.d("Thumb", txtThumb.toString());

            //ImageLoader

            String name = String.valueOf(i);
            String test = loadImageFromWebOperations(txtThumb, "StepForward/Cache"+name);


            //String Array daraus machen und in Hashmap füllen
            HashMap<String, Object> map = new HashMap<String, Object>();
            map.put("Thumb", test);
            map.put("Title", txtTitle);
            map.put("Content", txtContent);
            map.put("Link", txtLink);
            mylist.add(map);

        }
        //ListView füllen
        ListAdapter adapter = new SimpleAdapter(this, mylist , R.layout.lit, 
                new String[] { "Thumb","Title","Content","Link"}, 
                new int[] { R.id.img_video,R.id.txt_title,R.id.txt_subtitle});      
        setListAdapter(adapter);


        //OnClickLister um Youtube-Video zu öffnen
        final ListView lv = getListView();
            lv.setOnItemClickListener(new OnItemClickListener(){
                public void onItemClick(AdapterView<?> parent, View v, int position, long id) {

                    //Video-Link auslesen
                    Map<String, Object> map = mylist.get(position);
                    String link = (String) map.get("Link");
                    Log.d("Link", link);

                    //Link übergeben, Activity starter
                    final Intent Showvideo = new Intent(ChannelActivity.this, ShowVideo.class);
                    Showvideo.putExtra("VideoLink", link);
                    startActivity(Showvideo);


                }
            });


    }catch (Exception e) {
        Log.e("log_tag", "Error converting result " + e.toString());
        }
    }


    //Path-Loader
    public static String loadImageFromWebOperations(String url, String path) {
        try {
            InputStream is = (InputStream) new URL(url).getContent();

            System.out.println(path);
            File f = new File(Environment.getExternalStorageDirectory(), path);

            f.createNewFile();
            FileOutputStream fos = new FileOutputStream(f);
            try {

                byte[] b = new byte[100];
                int l = 0;
                while ((l = is.read(b)) != -1)
                    fos.write(b, 0, l);

            } catch (Exception e) {

            }

            return f.getAbsolutePath();
        } catch (Exception e) {
            System.out.println("Exc=" + e);
            return null;

        }
    }

}

Answer 1

Accessing files on external storage

If the user uninstalls your application, this directory and all its contents will be deleted.

on API level 8 or greater use the external cache directory: http://developer.android.com/guide/topics/data/data-storage.html#ExternalCache

There is also an explanation for using API level 7 and lower in the above link

Answer 2

You should not perform time consuming operations in onCreate or onDestroy. See http://developer.android.com/guide/practices/design/responsiveness.html for information on the App is not responding error.

Use an AsyncTask to delete the files, i.e. only start the execution of the deletion of the files in your onDestroy method. Also you should use an AsyncTask when loading the data.

See here for more information on Threads and processes in Android: http://developer.android.com/guide/topics/fundamentals/processes-and-threads.html