不幸的是，由于nullPointerException，我的应用已停止工作

Question

我正在尝试从服务器获取图像并将其加载到gridview中，但我的应用程序没有响应。我正在使用picasso库加载图像。

这是我的ImageAdapter类

package com.example.haha;

public class ImageAdapter extends BaseAdapter {

    private Context context;

    int length;
    String[] poster_paths=null;

    public ImageAdapter(Context c) {
        context = c;
        new BackgroundTask().execute();
    }

    public int getCount(){
        return length;
        }

    public Object getItem(int position) {
        return null;
    }

    public long getItemId(int position) {
        return 0;
    }

    public View getView(int position, View convertView, ViewGroup parent){
        //ImageView image;
        LayoutInflater inflater = (LayoutInflater) context
                .getSystemService(Context.LAYOUT_INFLATER_SERVICE);

        if(convertView==null)
        convertView=(ImageView)inflater.inflate(R.layout.gridviewitem, null);



        Picasso.with(context)  //USING PICASSO LIBRARY
        .load("http://image.tmdb.org/t/p/w185/"+ poster_paths[position]) 
        .placeholder(R.drawable.ic_launcher)
        .into((ImageView)convertView);

        return convertView;
    }


    public class BackgroundTask extends AsyncTask<String, Void, String[]>{


        final String BASE_URL="http://api.themoviedb.org/3/discover/movie?"
                + "sort_by=popularity.desc&api_key=b6c282dc7fb604515fdcf8d8cf56e761";


         private String[] jsonParse(String movieJsonStr) throws JSONException{

            final String POSTER_PATH="poster_path";  //JSON STRING PARSING AND RETURN 
                                                     //POSTER PATHS

            JSONObject jsonObj=new JSONObject(movieJsonStr);
            JSONArray resultArray= jsonObj.getJSONArray("results");

            length=resultArray.length();
            String[] poster_paths= new String[length];
            for(int i=0;i<length;i++){
                poster_paths[i]=resultArray.getJSONObject(i).getString(POSTER_PATH);
            }

            for(String res : poster_paths)
            Log.v(POSTER_PATH, res);    

            return poster_paths;
        }


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

            String movieJsonStr = null;

            BufferedReader reader = null;
            HttpURLConnection urlConnection = null; // READ THE INPUTSTREAM AND
                                                    // GET THE JSONSTRING
            try {
                URL url = new URL(BASE_URL);
                urlConnection = (HttpURLConnection) url.openConnection();
                urlConnection.setRequestMethod("GET");
                urlConnection.connect();

                // Read the input stream into a String
                InputStream inputStream = urlConnection.getInputStream();
                StringBuffer buffer = new StringBuffer();
                if (inputStream == null) {
                    // Nothing to do.
                    return null;
                }

                reader = new BufferedReader(new InputStreamReader(inputStream));

                String line;
                while ((line = reader.readLine()) != null) {
                    // Since it's JSON, adding a newline isn't necessary (it
                    // won't affect parsing)
                    // But it does make debugging a *lot* easier if you print
                    // out the completed
                    // buffer for debugging.
                    buffer.append(line + "\n");
                }

                if (buffer.length() == 0) {
                    // Stream was empty. No point in parsing.
                    return null;
                }

                movieJsonStr = buffer.toString();
                Log.v("Movie string: ", movieJsonStr);
            } catch (Throwable e) {
                Log.e("backgroundtask", "EXCEPTION", e);
            } finally {
                urlConnection.disconnect();
                try {
                    reader.close();
                } catch (IOException e) {
                    Log.e("READER.CLOSE()", e.toString());
                }
            }

            try {
                return jsonParse(movieJsonStr);
            } catch (JSONException e) {
                Log.e("BACKGROUNDTASK", "EXCEPTION FROM jsonParse()", e);
            }

            return null;
        }

        @Override
        protected void onPostExecute(String[] result) {
            if(result!=null)
            poster_paths=result;
            }

        }

}

这是我的logcat

08-01 03:04:56.108: D/AndroidRuntime(2588): Shutting down VM
08-01 03:04:56.108: E/AndroidRuntime(2588): FATAL EXCEPTION: main
08-01 03:04:56.108: E/AndroidRuntime(2588): Process: com.example.haha, PID: 2588
08-01 03:04:56.108: E/AndroidRuntime(2588): java.lang.NullPointerException: Attempt to read from null array
08-01 03:04:56.108: E/AndroidRuntime(2588):     at com.example.haha.ImageAdapter.getView(ImageAdapter.java:62)
08-01 03:04:56.108: E/AndroidRuntime(2588):     at android.widget.AbsListView.obtainView(AbsListView.java:2344)
08-01 03:04:56.108: E/AndroidRuntime(2588):     at android.widget.GridView.onMeasure(GridView.java:1060)
08-01 03:04:56.108: E/AndroidRuntime(2588):     at android.view.View.measure(View.java:17430)
08-01 03:04:56.108: E/AndroidRuntime(2588):     at android.view.ViewGroup.measureChildWithMargins(ViewGroup.java:5463)
08-01 03:04:56.108: E/AndroidRuntime(2588):     at android.widget.FrameLayout.onMeasure(FrameLayout.java:430)
08-01 03:04:56.108: E/AndroidRuntime(2588):     at android.view.View.measure(View.java:17430)
08-01 03:04:56.108: E/AndroidRuntime(2588):     at android.view.ViewGroup.measureChildWithMargins(ViewGroup.java:5463)
08-01 03:04:56.108: E/AndroidRuntime(2588):     at android.widget.FrameLayout.onMeasure(FrameLayout.java:430)
08-01 03:04:56.108: E/AndroidRuntime(2588):     at android.support.v7.internal.widget.ContentFrameLayout.onMeasure(ContentFrameLayout.java:124)
08-01 03:04:56.108: E/AndroidRuntime(2588):     at android.view.View.measure(View.java:17430)
08-01 03:04:56.108: E/AndroidRuntime(2588):     at android.view.ViewGroup.measureChildWithMargins(ViewGroup.java:5463)
08-01 03:04:56.108: E/AndroidRuntime(2588):     at android.support.v7.internal.widget.ActionBarOverlayLayout.onMeasure(ActionBarOverlayLayout.java:444)
08-01 03:04:56.108: E/AndroidRuntime(2588):     at android.view.View.measure(View.java:17430)
08-01 03:04:56.108: E/AndroidRuntime(2588):     at android.view.ViewGroup.measureChildWithMargins(ViewGroup.java:5463)
08-01 03:04:56.108: E/AndroidRuntime(2588):     at android.widget.FrameLayout.onMeasure(FrameLayout.java:430)
08-01 03:04:56.108: E/AndroidRuntime(2588):     at android.view.View.measure(View.java:17430)
08-01 03:04:56.108: E/AndroidRuntime(2588):     at android.view.ViewGroup.measureChildWithMargins(ViewGroup.java:5463)
08-01 03:04:56.108: E/AndroidRuntime(2588):     at android.widget.LinearLayout.measureChildBeforeLayout(LinearLayout.java:1436)
08-01 03:04:56.108: E/AndroidRuntime(2588):     at android.widget.LinearLayout.measureVertical(LinearLayout.java:722)
08-01 03:04:56.108: E/AndroidRuntime(2588):     at android.widget.LinearLayout.onMeasure(LinearLayout.java:613)
08-01 03:04:56.108: E/AndroidRuntime(2588):     at android.view.View.measure(View.java:17430)
08-01 03:04:56.108: E/AndroidRuntime(2588):     at android.view.ViewGroup.measureChildWithMargins(ViewGroup.java:5463)
08-01 03:04:56.108: E/AndroidRuntime(2588):     at android.widget.FrameLayout.onMeasure(FrameLayout.java:430)
08-01 03:04:56.108: E/AndroidRuntime(2588):     at com.android.internal.policy.impl.PhoneWindow$DecorView.onMeasure(PhoneWindow.java:2560)
08-01 03:04:56.108: E/AndroidRuntime(2588):     at android.view.View.measure(View.java:17430)
08-01 03:04:56.108: E/AndroidRuntime(2588):     at android.view.ViewRootImpl.performMeasure(ViewRootImpl.java:2001)
08-01 03:04:56.108: E/AndroidRuntime(2588):     at android.view.ViewRootImpl.measureHierarchy(ViewRootImpl.java:1166)
08-01 03:04:56.108: E/AndroidRuntime(2588):     at android.view.ViewRootImpl.performTraversals(ViewRootImpl.java:1372)
08-01 03:04:56.108: E/AndroidRuntime(2588):     at android.view.ViewRootImpl.doTraversal(ViewRootImpl.java:1054)
08-01 03:04:56.108: E/AndroidRuntime(2588):     at android.view.ViewRootImpl$TraversalRunnable.run(ViewRootImpl.java:5779)
08-01 03:04:56.108: E/AndroidRuntime(2588):     at android.view.Choreographer$CallbackRecord.run(Choreographer.java:767)
08-01 03:04:56.108: E/AndroidRuntime(2588):     at android.view.Choreographer.doCallbacks(Choreographer.java:580)
08-01 03:04:56.108: E/AndroidRuntime(2588):     at android.view.Choreographer.doFrame(Choreographer.java:550)
08-01 03:04:56.108: E/AndroidRuntime(2588):     at android.view.Choreographer$FrameDisplayEventReceiver.run(Choreographer.java:753)
08-01 03:04:56.108: E/AndroidRuntime(2588):     at android.os.Handler.handleCallback(Handler.java:739)
08-01 03:04:56.108: E/AndroidRuntime(2588):     at android.os.Handler.dispatchMessage(Handler.java:95)
08-01 03:04:56.108: E/AndroidRuntime(2588):     at android.os.Looper.loop(Looper.java:135)
08-01 03:04:56.108: E/AndroidRuntime(2588):     at android.app.ActivityThread.main(ActivityThread.java:5221)
08-01 03:04:56.108: E/AndroidRuntime(2588):     at java.lang.reflect.Method.invoke(Native Method)
08-01 03:04:56.108: E/AndroidRuntime(2588):     at java.lang.reflect.Method.invoke(Method.java:372)
08-01 03:04:56.108: E/AndroidRuntime(2588):     at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:899)
08-01 03:04:56.108: E/AndroidRuntime(2588):     at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:694)
08-01 03:04:56.109: W/ActivityManager(1226):   Force finishing activity com.example.haha/.Main
08-01 03:04:56.110: W/ActivityManager(1226):   Force finishing activity com.example.haha/.MainActivity

logcat表示在访问getView方法中的字符串数组poster_paths时存在nullpointerException，因为它是一个空数组，但是在postexecute方法中，poster_paths数组被分配了字符串，请帮助...。

Answer 1

您正在隐藏变量poster_paths 。 更换

String[] poster_paths= new String[length];

同

posterPaths = new String[length];