我从我的服务器上的PHP脚本json对象生成，然后用延迟加载的图像解析成一个列表视图。的问题是，JSON将加载比较快的，否则它将挂起第二或两个取决于服务器上的响应，其可以是令人沮丧的。当我第一次打开应用程序的窍门是espcially烦人，因为它会挂在黑屏，直至对象已被加载，然后当我更新的应用程序，它具有相同的，但至少认为已加载的列表。这是我的code，以获得JSON：

I take json object generate from a PHP script on my server and then parse it into a listview using a lazy load for the images. The problem is that the json will load relatively fast or it will hang for second or two depending on the response on the server, which can be frustrating. When I first open the app the hang is espcially annoying because it will hang at a black screen until the object has been loaded and then when I update the list in app it has the same but at least the view has been loaded. Here is my code to get the json:

public void getJson(String selection, String url) {
    JSONObject json = null;
    String formatedcat = selection.toLowerCase();
    ArrayList<HashMap<String, String>> mylist = new ArrayList<HashMap<String, String>>();
    json = JSONfunctions
            .getJSONfromURL(url);
    try {
        //the array title that you parse
        JSONArray category = json.getJSONArray(formatedcat);
        for (int i = 0; i < category.length(); i++) {               
            HashMap<String, String> map = new HashMap<String, String>();
            JSONObject c = category.getJSONObject(i);
            map.put("id", String.valueOf(i));
            map.put("name",
                    c.getString("title"));
            //map.put("text",c.getString("title"));
            map.put("ts",c.getString("run_date") );
            map.put("image","http:"+c.getString("url"));
            mylist.add(map);
        }
    } catch (JSONException e) {

    }
    ListAdapter adapter = new JsonAdapter(this, mylist, R.layout.list,
            new String[] { "name", "text", "ts"}, new int[] { R.id.item_title,
                    R.id.item_subtitle, R.id.timestamp});
    setListAdapter(adapter);        
}

适配器code：

Adapter Code:

public class JsonAdapter extends SimpleAdapter {

    public ImageManager imageManager;
    public ListActivity context;
    public ArrayList<HashMap<String,String>> list;
    public String[] fieldNames;
    public int[] fieldTargetIds;

    public JsonAdapter(ListActivity c, 
            ArrayList<HashMap<String, String>> mylist,
            int textViewResourceId,
            String[] fieldNames,
            int[] fieldTargetIds) {
        super(c, mylist, textViewResourceId, fieldNames, fieldTargetIds );
        this.context = c;
        this.list = mylist;
        this.fieldNames = fieldNames;
        this.fieldTargetIds = fieldTargetIds;
        this.imageManager = new ImageManager(context.getApplicationContext());
    }

    @Override
    public View getView(int position, View convertView, ViewGroup parent) {

        View row = convertView;
        if (row == null) {
            LayoutInflater vi = (LayoutInflater) getSystemService(Context.LAYOUT_INFLATER_SERVICE);
            row = vi.inflate(R.layout.list, null);
        }
        //super.getView(position, convertView, parent);
        ImageView imgView = (ImageView) row.findViewById(R.id.doodlepic);

        try {
            String url = list.get(position).get("image");
            imgView.setTag(url);
            imageManager.displayImage(url, context, imgView);
        } catch (Exception e) {

        }

        for (int i=0; i<fieldNames.length; i++) {
            TextView tv = (TextView) row.findViewById(fieldTargetIds[i]);
            tv.setText(list.get(position).get(fieldNames[i]));              
        }


        return row;
    }

}

我怎么能实现异步任务显示一个进度对话框，而正在生成并下载了JSON对象？我已经使用线程和异步任务的尝试，但我不能完全弄清楚如何掰开我的code到相应的部分。

How could I implement an async task to show a progress dialog while the json object is being generated and downloaded? I've tried using threads and Async task but I can't quite figure out how to break apart my code into the appropriate parts.

推荐答案

上的preExecute，的AsyncTask的onPostExecute将在UI线程中运行，在doInBackground将在另一个线程中运行，因此低于code应该只是替你安排

The onPreExecute , onPostExecute of AsyncTask will run in the UI thread, the doInBackground will run in another thread, so below code should just fine for you

public class YourActivity extends Activiy{
   public void getJson(String selection, String url) { 
           new LoadJsonTask().execute( selection, url);

   }
   private class LoadJsonTask extends AsyncTask<String, Void, ArrayList<HashMap<String, String>> > {
       ProgressDialog dialog ;
       protected void onPreExecute (){
            dialog = ProgressDialog.show(YourActivity.this ,"title","message");

       }
       protected ArrayList<HashMap<String, String>> doInBackground (String... params){
           return doGetJson(params[0],params[1]);
       }
       protected void onPostExecute(ArrayList<HashMap<String, String>> mylist){

            ListAdapter adapter = new JsonAdapter(YourActivity.this, mylist, R.layout.list,
              new String[] { "name", "text", "ts"}, new int[] { R.id.item_title,
                R.id.item_subtitle, R.id.timestamp});
            setListAdapter(adapter);
            dialog.dismiss();
       }
    }

 public ArrayList<HashMap<String, String>> doGetJson(String selection, String url) {
     JSONObject json = null;
     String formatedcat = selection.toLowerCase();
     ArrayList<HashMap<String, String>> mylist = new ArrayList<HashMap<String, String>>();
     json = JSONfunctions
        .getJSONfromURL(url);
     try {
    //the array title that you parse
    JSONArray category = json.getJSONArray(formatedcat);
    for (int i = 0; i < category.length(); i++) {               
        HashMap<String, String> map = new HashMap<String, String>();
        JSONObject c = category.getJSONObject(i);
        map.put("id", String.valueOf(i));
        map.put("name",
                c.getString("title"));
        //map.put("text",c.getString("title"));
        map.put("ts",c.getString("run_date") );
        map.put("image","http:"+c.getString("url"));
        mylist.add(map);
    }
} catch (JSONException e) {

}
   return mylist;
  ....   
}