清除“缓存”销毁时

Question

我尝试做的事情

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我正在为我的频道构建一个应用程序。我通过 JSON 从 google 获取数据，然后通过 SimpleAdapter 将其填充到我的 ListView 中。

我可以在我的 SimpleAdapter 中显示图片，我将它们保存到我的 SDCard 上。现在的问题是，当应用程序被杀死时，我会收到强制关闭错误，因为图片已经在那里了。

问题

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如何在 onDestroy() 上删除 SDCard 上的“缓存”图像？

您可以在此处找到应用程序的代码。提前感谢您的帮助！

代码

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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

访问外部存储上的文件

如果用户卸载您的应用程序，该目录及其所有内容都将被删除。

在 API 级别 8 或更高级别上，使用外部缓存目录： http:// /developer.android.com/guide/topics/data/data-storage.html#ExternalCache

上面的链接中还有使用 API 级别 7 及更低级别的说明

Answer 2

您不应该在 onCreate 或 onDestroy 中执行耗时的操作。请参阅http://developer.android.com/guide/practices/design/responsiveness。 html 有关应用程序未响应错误的信息。

使用AsyncTask删除文件，即仅在onDestroy方法中开始执行文件的删除。加载数据时还应该使用 AsyncTask。

有关 Android 中线程和进程的更多信息，请参阅此处：http:// /developer.android.com/guide/topics/fundamentals/processes-and-threads.html