Question

我的应用中有自定义列表视图。我使用http请求以JSON格式获取数据。有一个asynctask来加载listview的整个数据（图像除外）。

在这个asyntask的onpostexecute（）中，我调用了另一个asynctask来获取listview的图像。

现在我尝试使用textchangedlistener

在listview上实现搜索功能

问题是图像在后台加载，我经常遇到空指针异常。

任何人都可以建议我摆脱这种方法。我目前正在做的是，我没有显示searchbox edittext，直到加载图像。但是这会让用户等待很多，特别是对于长列表。

整个代码太长而无法发布。所以，我只是在这里粘贴它的简要概述。如果您还有其他需要，请告诉我。我也会这样做。

public class abcd extends Activity {
    ListView todlistview;
    List<HashMap<String, Object>> cnt = null;
    ArrayList<HashMap<String, Object>> searchResults; /

    .
    .




     /** AsyncTask to parse json data and load ListView */
    private class ListViewLoaderTask extends AsyncTask<String, Void, SimpleAdapter>{


        @Override
        protected SimpleAdapter doInBackground(String... strJson) {
        .
        .
        .

            adapter = new SimpleAdapter(getBaseContext(), cnt, com.example.promoapp.R.layout.textviewfield, from, to);

            return adapter;
        }

        @Override
        protected void onPostExecute(SimpleAdapter adapter) {

            searchResults=new ArrayList<HashMap<String, Object>> (cnt);

            // Setting adapter for the listview
            todlistview.setAdapter(adapter);

            for(int i=0;i<adapter.getCount();i++){
                HashMap<String, Object> hm = (HashMap<String, Object>) adapter.getItem(i);
                .
        .


        ImageLoaderTask imageLoaderTask = new ImageLoaderTask();
                // Starting ImageLoaderTask to download and populate image in the listview
                imageLoaderTask.execute(hm); 
            }
        }
    }

    /** AsyncTask to download and load an image in ListView */
    private class ImageLoaderTask extends AsyncTask<HashMap<String, Object>, Void, HashMap<String, Object>>{

        Dialog dil;
        @Override
        protected HashMap<String, Object> doInBackground(HashMap<String, Object>... hm) {

            InputStream iStream=null;
                  .


                // Create a hashmap object to store image path and its position in the listview
                // Storing the path to the temporary image file
                // Storing the position of the image in the listview
                // Returning the HashMap object containing the image path and position

        }

        @Override
        protected void onPostExecute(HashMap<String, Object> result) {

        }



    }


    private TextWatcher filterTextWatcher = new TextWatcher() {

            @Override
            public void onTextChanged(CharSequence s, int start, int before,
                    int count) {

        String searchString=Search.getText().toString();
                int textLength=searchString.length();               

                searchResults.clear();

                for(int i=0;i<cnt.size();i++)
                {
                    String placeName=cnt.get(i).get("country").toString();

                    if(textLength<=placeName.length()){
                        //compare the String in EditText with Names in the ArrayList
                        if(searchString.equalsIgnoreCase(placeName.substring(0,textLength))){
                            //Toast.makeText(getApplicationContext(),placeName,1).show();
                            searchResults.add(cnt.get(i));
                        }
                    }
                }

                String[] from = { "country","flag","details"};
                 int[] to = { com.example.promoapp.R.id.tv_country,com.example.promoapp.R.id.iv_flag,com.example.promoapp.R.id.tv_country_details};
                 adapter = new SimpleAdapter(getBaseContext(), searchResults, com.example.promoapp.R.layout.textviewfield, from, to);
                 todlistview.setAdapter(adapter);
                adapter.notifyDataSetChanged(); 
              }
     };


}

Answer 1

首先，我不会在 onPostExecute 中执行像图像加载这样繁重的任务，因为此方法适用于UI线程。您只需使用ImageLoaderTask阻止UI。我会尝试在第一个AsyncTask中加载图像和其他所有内容。问题是您正在同时搜索和修改列表。尝试加载ListViewLoaderTask的 onBackground

Android：无法在延迟加载列表视图上实现搜索

1 个答案: