Android 显示图像列表视图窗口

我很难解决这个问题，我希望有人能向我解释这个问题。我有这个解析JSON的代码，用这个代码我应该可以得到值

public class MainActivity extends Activity {
// Declare Variables
JSONObject jsonobject;
JSONArray jsonarray;
ListView listview;

JSONParser jParser = new JSONParser();

ListViewAdapter adapter;
ProgressDialog mProgressDialog;
ArrayList<HashMap<String, String>> arraylist;

static String RANK = "rank";
static String COUNTRY = "country";
static String POPULATION = "population";
static String FLAG = "flag";
static final String TAG_fraction_id = "fraction_id";
static final String TAG_fraction_name = "fraction_name";
static final String TAG_fraction_type = "fraction_type";
static final String TAG_fraction_typetext = "fraction_typetext";
static final String TAG_fraction_description = "fraction_description";
static final String TAG_fraction_extra = "fraction_extra";
static final String TAG_fraction_company_id = "company_id";
static final String TAG_fraction_pictogram = "fraction_pictogram";
static final String TAG_Company = "company_id";

@Override
public void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    // Get the view from listview_main.xml
    setContentView(R.layout.listview_main);
    // Execute DownloadJSON AsyncTask
    new DownloadJSON().execute();

}

// DownloadJSON AsyncTask
private class DownloadJSON extends AsyncTask<String, String, String> {

    @Override
    protected void onPreExecute() {
        super.onPreExecute();
        // Create a progressdialog
        mProgressDialog = new ProgressDialog(MainActivity.this);
        // Set progressdialog title
        mProgressDialog.setTitle("Android JSON Parse Tutorial");
        // Set progressdialog message
        mProgressDialog.setMessage("Loading...");
        mProgressDialog.setIndeterminate(false);
        // Show progressdialog
        mProgressDialog.show();
    }

    @Override
    protected String doInBackground(String... params) {

        String url = "http://ws.mitaffald.dk/webservice/getFractions.php?company_id=0";
        JSONArray json = jParser.getJSONFromUrl(url);
        try {
               for(int i = 0; i < json.length(); i++){
                    JSONObject c = json.getJSONObject(i);

              String fraction_id = c.getString(TAG_fraction_id);
              String fraction_name = c.getString(TAG_fraction_name);
              String fraction_type = c.getString(TAG_fraction_type);
              String fraction_typetext = c.getString(TAG_fraction_typetext);
              String fraction_description = c.getString(TAG_fraction_description);  
              String fraction_extra = c.getString(TAG_fraction_extra);
              String company_id = c.getString(TAG_fraction_company_id);
              String fraction_pictogram = c.getString(TAG_fraction_pictogram);

              HashMap<String, String> map = new HashMap<String, String>();

                // Hver knode blive lavet til nøgle : værdi 
                map.put(TAG_fraction_id, fraction_id);
                map.put(TAG_fraction_name, fraction_name);
                map.put(TAG_fraction_type, fraction_type);
                map.put(TAG_fraction_typetext, fraction_typetext);
                map.put(TAG_fraction_description, fraction_description);
                map.put(TAG_fraction_extra, fraction_extra);
                map.put(TAG_fraction_company_id, company_id);
                map.put(TAG_fraction_pictogram, fraction_pictogram);

                // tilføj til arraylist
                arraylist.add(map);
            }
        } catch (JSONException e) {
            Log.e("Error", e.getMessage());
            e.printStackTrace();
        }
        return null;
    }

    @Override
    protected void onPostExecute(String file_url) {
        mProgressDialog.dismiss();
        // Locate the listview in listview_main.xml
        listview = (ListView) findViewById(R.id.listview);
        // Pass the results into ListViewAdapter.java
        adapter = new ListViewAdapter(MainActivity.this, arraylist);
        // Binds the Adapter to the ListView
        listview.setAdapter(adapter);
    }
}

公共类MainActivity扩展活动{
//声明变量
JSONObject JSONObject；
JSONArray JSONArray；
列表视图列表视图；
JSONParser jParser=新的JSONParser（）；
ListViewAdapter适配器；
进程对话框；
ArrayList ArrayList；
静态字符串RANK=“RANK”；
静态字符串COUNTRY=“COUNTRY”；
静态字符串POPULATION=“POPULATION”；
静态字符串FLAG=“FLAG”；
静态最终字符串标记\u分数\u id=“分数\u id”；
静态最终字符串标记\分数\名称=“分数\名称”；
静态最终字符串标记\分数\类型=“分数\类型”；
静态最终字符串标记\u分数\u类型文本=“分数\u类型文本”；
静态最终字符串标记\分数\描述=“分数\描述”；
静态最终字符串标记\u分数\u额外=“分数\u额外”；
静态最终字符串标记\u分数\u公司\u id=“公司\u id”；
静态最终字符串标记\分数\象形图=“分数\象形图”；
静态最终字符串标记\u Company=“Company\u id”；
@凌驾
创建时的公共void（Bundle savedInstanceState）{
super.onCreate（savedInstanceState）；
//从listview_main.xml获取视图
setContentView（R.layout.listview_main）；
//执行下载JSON异步任务
新建下载JSON（）.execute（）；
}
//下载JSON异步任务
私有类下载JSON扩展异步任务{
@凌驾
受保护的void onPreExecute（）{
super.onPreExecute（）；
//创建一个progressdialog
mProgressDialog=新建ProgressDialog（MainActivity.this）；
//设置进程对话框标题
setTitle（“Android JSON解析教程”）；
//设置进程对话框消息
设置消息（“加载…”）；
mProgressDialog.setUndeterminate（false）；
//显示进度对话框
mProgressDialog.show（）；
}
@凌驾
受保护的字符串doInBackground（字符串…参数）{
字符串url=”http://ws.mitaffald.dk/webservice/getFractions.php?company_id=0";
JSONArray json=jParser.getJSONFromUrl（url）；
试一试{
for（int i=0；i

但当我运行时，我会遇到以下错误：

    07-12 00:05:03.480: E/AndroidRuntime(30716): FATAL EXCEPTION: AsyncTask #1
    07-12 00:05:03.480: E/AndroidRuntime(30716): java.lang.RuntimeException: An error occured while executing doInBackground()
    07-12 00:05:03.480: E/AndroidRuntime(30716):    at         android.os.AsyncTask$3.done(AsyncTask.java:299)
    07-12 00:05:03.480: E/AndroidRuntime(30716):    at java.util.concurrent.FutureTask$Sync.innerSetException(FutureTask.java:273)
    07-12 00:05:03.480: E/AndroidRuntime(30716):    at java.util.concurrent.FutureTask.setException(FutureTask.java:124)
    07-12 00:05:03.480: E/AndroidRuntime(30716):    at java.util.concurrent.FutureTask$Sync.innerRun(FutureTask.java:307)
    07-12 00:05:03.480: E/AndroidRuntime(30716):    at java.util.concurrent.FutureTask.run(FutureTask.java:137)
    07-12 00:05:03.480: E/AndroidRuntime(30716):    at android.os.AsyncTask$SerialExecutor$1.run(AsyncTask.java:230)
    07-12 00:05:03.480: E/AndroidRuntime(30716):    at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1076)
    07-12 00:05:03.480: E/AndroidRuntime(30716):    at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:569)
    07-12 00:05:03.480: E/AndroidRuntime(30716):    at java.lang.Thread.run(Thread.java:856)
    07-12 00:05:03.480: E/AndroidRuntime(30716): Caused by: java.lang.NullPointerException
    07-12 00:05:03.480: E/AndroidRuntime(30716):    at com.androidbegin.jsonparsetutorial.MainActivity$DownloadJSON.doInBackground(MainActivity.java:100)
    07-12 00:05:03.480: E/AndroidRuntime(30716):    at com.androidbegin.jsonparsetutorial.MainActivity$DownloadJSON.doInBackground(MainActivity.java:1)
    07-12 00:05:03.480: E/AndroidRuntime(30716):    at android.os.AsyncTask$2.call(AsyncTask.java:287)
    07-12 00:05:03.480: E/AndroidRuntime(30716):    at java.util.concurrent.FutureTask$Sync.innerRun(FutureTask.java:305)
    07-12 00:05:03.480: E/AndroidRuntime(30716):    ... 5 more
    07-12 00:05:03.495: D/dalvikvm(30716): GC_CONCURRENT freed 370K, 14% free 9890K/11463K, paused 11ms+2ms, total 35ms
    07-12 00:05:07.800: I/Choreographer(30716): Skipped 30 frames!  The application may be doing too much work on its main thread.
    07-12 00:05:12.425: E/WindowManager(30716): Activity com.androidbegin.jsonparsetutorial.MainActivity has leaked window com.android.internal.policy.impl.PhoneWindow$DecorView@42124d18 that was originally added here
    07-12 00:05:12.425: E/WindowManager(30716): android.view.WindowLeaked: Activity com.androidbegin.jsonparsetutorial.MainActivity has leaked window com.android.internal.policy.impl.PhoneWindow$DecorView@42124d18 that was originally added here
    07-12 00:05:12.425: E/WindowManager(30716):     at android.view.ViewRootImpl.<init>(ViewRootImpl.java:403)
    07-12 00:05:12.425: E/WindowManager(30716):     at android.view.WindowManagerImpl.addView(WindowManagerImpl.java:311)
    07-12 00:05:12.425: E/WindowManager(30716):     at android.view.WindowManagerImpl.addView(WindowManagerImpl.java:224)
    07-12 00:05:12.425: E/WindowManager(30716):     at android.view.WindowManagerImpl$CompatModeWrapper.addView(WindowManagerImpl.java:149)
    07-12 00:05:12.425: E/WindowManager(30716):     at android.view.Window$LocalWindowManager.addView(Window.java:554)
    07-12 00:05:12.425: E/WindowManager(30716):     at android.app.Dialog.show(Dialog.java:277)
    07-12 00:05:12.425: E/WindowManager(30716):     at com.androidbegin.jsonparsetutorial.MainActivity$DownloadJSON.onPreExecute(MainActivity.java:66)
    07-12 00:05:12.425: E/WindowManager(30716):     at android.os.AsyncTask.executeOnExecutor(AsyncTask.java:586)
    07-12 00:05:12.425: E/WindowManager(30716):     at android.os.AsyncTask.execute(AsyncTask.java:534)
    07-12 00:05:12.425: E/WindowManager(30716):     at com.androidbegin.jsonparsetutorial.MainActivity.onCreate(MainActivity.java:48)
    07-12 00:05:12.425: E/WindowManager(30716):     at android.app.Activity.performCreate(Activity.java:5206)
    07-12 00:05:12.425: E/WindowManager(30716):     at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1094)
    07-12 00:05:12.425: E/WindowManager(30716):     at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2074)
    07-12 00:05:12.425: E/WindowManager(30716):     at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2135)
    07-12 00:05:12.425: E/WindowManager(30716):     at android.app.ActivityThread.access$700(ActivityThread.java:140)
    07-12 00:05:12.425: E/WindowManager(30716):     at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1237)
    07-12 00:05:12.425: E/WindowManager(30716):     at android.os.Handler.dispatchMessage(Handler.java:99)
    07-12 00:05:12.425: E/WindowManager(30716):     at android.os.Looper.loop(Looper.java:137)
    07-12 00:05:12.425: E/WindowManager(30716):     at android.app.ActivityThread.main(ActivityThread.java:4921)
    07-12 00:05:12.425: E/WindowManager(30716):     at java.lang.reflect.Method.invokeNative(Native Method)
    07-12 00:05:12.425: E/WindowManager(30716):     at java.lang.reflect.Method.invoke(Method.java:511)
    07-12 00:05:12.425: E/WindowManager(30716):     at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:1027)
    07-12 00:05:12.425: E/WindowManager(30716):     at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:794)
    07-12 00:05:12.425: E/WindowManager(30716):     at dalvik.system.NativeStart.main(Native Method)

07-12 00:05:03.480:E/AndroidRuntime（30716）：致命异常：异步任务#1
07-12 00:05:03.480:E/AndroidRuntime（30716）：java.lang.RuntimeException:执行doInBackground（）时出错
07-12 00:05:03.480:E/AndroidRuntime（30716）：在android.os.AsyncTask$3.done（AsyncTask.java:299）
07-12 00:05:03.480:E/AndroidRuntime（30716）：位于java.util.concurrent.FutureTask$Sync.innerSetException（FutureTask.java:273）
07-12 00:05:03.480:E/AndroidRuntime（30716）：位于java.util.concurrent.FutureTask.setException（FutureTask.java:124）
07-12 00:05:03.480:E/AndroidRuntime（30716）：在java.util.concurrent.FutureTask$Sync.innerRun（FutureTask.java:307）
07-12 00:05:03.480:E/AndroidRuntime（30716）：在java.util.concurrent.FutureTask.run（FutureTask.java:137）
07-12 00:05:03.480:E/AndroidRuntime（30716）：在android.os.AsyncTask$SerialExecutor$1.run（AsyncTask.java:230）
07-12 00:05:03.480:E/AndroidRuntime（30716）：位于java.util.concurrent.ThreadPoolExecutor.runWorker（ThreadPoolExecutor.java:1076）
07-12 00:05:03.480:E/AndroidRuntime（30716）：位于java.util.concurrent.ThreadPoolExecutor$Worker.run（ThreadPoolExecutor.java:569）
07-12 00:05:03.480:E/AndroidRuntime（30716）：在java.lang.Thread.run（Thread.java:856）
07-12 00:05:03.480:E/AndroidRuntime（30716）：由以下原因引起：java.lang.NullPointerException
07-12 00:05:03.480:E/AndroidRuntime（30716）：在com.androidbegin.jsonparsetutorial.MainActivity$DownloadJSON.doInBackground（MainActivity.java:100）
07-12 00:05:03.480:E/AndroidRuntime（30716）：位于com.androidbegin.jsonparsetutorial.MainActivity$DownloadJSON.doInBackground（MainActivity.java:1）
07-12 00:05:03.480:E/AndroidRuntime（30716）：在android.os.AsyncTask$2.call（AsyncTask.java: