android - 使用通用图像加载器和 JSON 而不是 Constant Class

Question

我想使用通用图像加载器(UIL)来显示url存储在mysql数据库中的图像。带常量类的 UIL 演示效果很好。不过为了自己的目的稍作修改后就出现了一些错误。

错误信息为:

03-12 13:56:13.375: E/AndroidRuntime(31634): FATAL EXCEPTION: main
03-12 13:56:13.375: E/AndroidRuntime(31634): java.lang.RuntimeException: Unable to start activity ComponentInfo{com.example.test/com.example.test.ImageGridActivity}: java.lang.NullPointerException
03-12 13:56:13.375: E/AndroidRuntime(31634):    at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:1768)
03-12 13:56:13.375: E/AndroidRuntime(31634):    at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:1784)
03-12 13:56:13.375: E/AndroidRuntime(31634):    at android.app.ActivityThread.access$1500(ActivityThread.java:123)
03-12 13:56:13.375: E/AndroidRuntime(31634):    at android.app.ActivityThread$H.handleMessage(ActivityThread.java:939)
03-12 13:56:13.375: E/AndroidRuntime(31634):    at android.os.Handler.dispatchMessage(Handler.java:99)
03-12 13:56:13.375: E/AndroidRuntime(31634):    at android.os.Looper.loop(Looper.java:130)
03-12 13:56:13.375: E/AndroidRuntime(31634):    at android.app.ActivityThread.main(ActivityThread.java:3835)
03-12 13:56:13.375: E/AndroidRuntime(31634):    at java.lang.reflect.Method.invokeNative(Native Method)
03-12 13:56:13.375: E/AndroidRuntime(31634):    at java.lang.reflect.Method.invoke(Method.java:507)
03-12 13:56:13.375: E/AndroidRuntime(31634):    at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:864)
03-12 13:56:13.375: E/AndroidRuntime(31634):    at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:622)
03-12 13:56:13.375: E/AndroidRuntime(31634):    at dalvik.system.NativeStart.main(Native Method)
03-12 13:56:13.375: E/AndroidRuntime(31634): Caused by: java.lang.NullPointerException
03-12 13:56:13.375: E/AndroidRuntime(31634):    at com.example.test.ImageGridActivity.onCreate(ImageGridActivity.java:45)
03-12 13:56:13.375: E/AndroidRuntime(31634):    at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1047)
03-12 13:56:13.375: E/AndroidRuntime(31634):    at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:1722)
03-12 13:56:13.375: E/AndroidRuntime(31634):    ... 11 more

首先，ImageGridView.java是:

public class ImageGridActivity extends AbsListViewBaseActivity {

String[] imageUrls;

DisplayImageOptions options;

@Override
public void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.ac_image_grid);
    initView();

    // Retrieval data from the intent
    Bundle bundle = getIntent().getExtras();
     imageUrls = bundle.getStringArray(Commons.IMGURLS); ----> Line 45


    options = new DisplayImageOptions.Builder()
            .showImageOnLoading(R.drawable.ic_stub)
            .showImageForEmptyUri(R.drawable.ic_empty)
            .showImageOnFail(R.drawable.ic_error).cacheInMemory(true)
            .cacheOnDisc(true).considerExifParams(true)
            .bitmapConfig(Bitmap.Config.RGB_565).build();

    listView = (GridView) findViewById(R.id.gridView1);
    ((GridView) listView).setAdapter(new ImageAdapter());
    listView.setOnItemClickListener(new OnItemClickListener() {
        @Override
        public void onItemClick(AdapterView<?> parent, View view,
                int position, long id) {
             startImagePagerActivity(position);
        }
    });


}
private void initView() {
    String url = "http://192.168.2.200/test/app.php";
    FetchDataTask task = new FetchDataTask(this);
    task.execute(url);
}


 private void startImagePagerActivity(int position) {
     Intent intent = new Intent(this, ImagePagerActivity.class);
     intent.putExtra(Extra.IMAGES, imageUrls);
     intent.putExtra(Extra.IMAGE_POSITION, position);
     startActivity(intent);
 }

//public class ImageAdapter extends BaseAdapter {
 public class ImageAdapter extends BaseAdapter {

    public int getCount() {         
        Log.d("hui", "getcount = " + Integer.toString(imageUrls.length));
        return imageUrls.length;
    }

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

    @Override
    public long getItemId(int position) {
        return position;
    }

    @Override
    public View getView(int position, View convertView, ViewGroup parent) {
        final ViewHolder holder;
        View view = convertView;
        if (view == null) {
            view = getLayoutInflater().inflate(R.layout.item_image_grid, parent, false);
            holder = new ViewHolder();
            assert view != null;
            holder.imageView = (ImageView) view.findViewById(R.id.imageView1);
            holder.progressBar = (ProgressBar) view.findViewById(R.id.progress);
            view.setTag(holder);
        } else {
            holder = (ViewHolder)view.getTag();
        }


             imageLoader.displayImage(imageUrls[position],   
            holder.imageView,
             options, new SimpleImageLoadingListener() {
            @Override
            public void onLoadingStarted(String imageUri,
                    View view) {
            holder.progressBar.setProgress(0);
            holder.progressBar.setVisibility(View.VISIBLE);
            }

            @Override
            public void onLoadingFailed(String imageUri,
            View view, FailReason failReason) {
            holder.progressBar.setVisibility(View.GONE);
            }

             @Override
             public void onLoadingComplete(String imageUri,
             View view, Bitmap loadedImage) {
             holder.progressBar.setVisibility(View.GONE);
             }
            }, new ImageLoadingProgressListener() {
            @Override
            public void onProgressUpdate(String imageUri,
            View view, int current, int total) {
            holder.progressBar.setProgress(Math
            .round(100.0f * current / total));
            }
            });




        return view;
    }

    class ViewHolder {
        ImageView imageView;
        ProgressBar progressBar;
    }

}

}

我还实现了一个 fetchDataTask 类，它是 AsyncTask 的子类。代码是

public class FetchDataTask extends AsyncTask<String, Void, String> {
ArrayList<HashMap<String, String>>hashMaps;
ArrayList<String> urlArrayList;
String [] urlStrings;
String urlString;
Intent intent;
ProgressDialog loDialog;
private Context context;

JSONObject jsonObject;
JSONArray jsonArray;



public FetchDataTask(Context context) {     
    this.context = context;
}

@Override
protected void onPreExecute(){
    super.onPreExecute();
    loDialog = new ProgressDialog(context);
    loDialog.setMessage("Loading Images...");
    loDialog.setIndeterminate(false);
    loDialog.show();
}


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

    if (params == null)
        return null;

    // get url from params
    String url = params[0];

    try {
        // create http connection
        HttpClient client = new DefaultHttpClient();
        HttpGet httpget = new HttpGet(url);

        // connect
        HttpResponse response = client.execute(httpget);

        // get response
        HttpEntity entity = response.getEntity();

        if (entity == null) {
            return null;
        }

        // get response content and convert it to json string
        InputStream is = entity.getContent();
        Log.i("hui", streamToString(is));
        return streamToString(is);
    } catch (IOException e) {
        e.printStackTrace();
    }

    return null;
}

@Override
protected void onPostExecute(String sJson) {


    try {
        // convert json string to json array
        JSONArray aJson = new JSONArray(sJson);             
        urlArrayList = new ArrayList<String>();

        for (int i = 0; i < aJson.length(); i++) {
            JSONObject json = aJson.getJSONObject(i);
            HashMap<String, String> hash= new HashMap<String, String>();

            hash.put("img_url", json.getString("img_url"));             
            hashMaps.add(hash);
            urlString = json.getString("img_url");
            urlArrayList.add(urlString);

            urlStrings = urlArrayList.toArray(new String [urlArrayList.size()]);
        }

        intent = new Intent(context, ImageGridActivity.class);
        intent.putExtra(Commons.IMGURLS, urlStrings);
        context.startActivity(intent);


        // notify the activity that fetch data has been complete
//      if (listener != null)
//          listener.onFetchComplete(imgfromServersList);
    } catch (JSONException e) {
        e.printStackTrace();
    }
}

/**
 * This function will convert response stream into json string
 * 
 * @param is
 *            respons string
 * @return json string
 * @throws IOException
 */
public String streamToString(final InputStream is) throws IOException {
    BufferedReader reader = new BufferedReader(new InputStreamReader(is));
    StringBuilder sb = new StringBuilder();
    String line = null;

    try {
        while ((line = reader.readLine()) != null) {
            sb.append(line + "\n");
        }
    } catch (IOException e) {
        throw e;
    } finally {
        try {
            is.close();
        } catch (IOException e) {
            throw e;
        }
    }

    return sb.toString();
}

///public class data

}

Json数据的一些示例如下:

[{"img_url":"http:\/\/192.168.2.200\/test\/imgs\/1.png"},{"img_url":"http:\/\/192.168.2.200\/test\/imgs\/2.png"},{"img_url":"http:\/\/192.168.2.200\/test\/imgs\/3.png"},{"img_url":"http:\/\/192.168.2.200\/test\/imgs\/4.png"},{"img_url":"http:\/\/192.168.2.200\/test\/imgs\/5.png"},{"img_url":"http:\/\/192.168.2.200\/test\/imgs\/6.png"},{"img_url":"http:\/\/192.168.2.200\/test\/imgs\/7.png"},{"img_url":"http:\/\/192.168.2.200\/test\/imgs\/8.png"},{"img_url":"http:\/\/192.168.2.200\/test\/imgs\/9.png"},{"img_url":"http:\/\/192.168.2.200\/test\/imgs\/10.png"},{"img_url":"http:\/\/192.168.2.200\/test\/imgs\/11.png"},{"img_url":"http:\/\/192.168.2.200\/test\/imgs\/12.png"},{"img_url":"http:\/\/192.168.2.200\/test\/imgs\/13.png"},{"img_url":"http:\/\/192.168.2.200\/test\/imgs\/14.png"},{"img_url":"http:\/\/192.168.2.200\/test\/imgs\/15.png"},{"img_url":"http:\/\/192.168.2.200\/test\/imgs\/16.png"},{"img_url":"http:\/\/192.168.2.200\/test\/imgs\/17.png"},{"img_url":"http:\/\/192.168.2.200\/test\/imgs\/18.png"},{"img_url":"http:\/\/192.168.2.200\/test\/imgs\/19.png"},{"img_url":"http:\/\/192.168.2.200\/test\/imgs\/20.png"}]

但是，代码不起作用，我不知道为什么。有什么建议吗？

Answer 1

我猜你的错误是关于你如何尝试在 Android Activity 之间传递字符串数组，例如:

• 传递数据:

  bundle = new Bundle();

  bundle.putStringArray("tag", urlStrings);

  Intent =new Intent(yourMainActivity.this, yourActivityToGetData.class);

  intend.putExtras(bundle);

• 读取数据:

  bundle = this.getIntent().getExtras();

  String[] array=bundle.getStringArray("tag");

<小时/>

在您的 ImageGridActivity 中:

@Override
public void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.ac_image_grid);
    initView();

    FetchDataTask task = new FetchDataTask(ImageGridActivity.this);
    task.execute(url);

    ...

在您的 FetchDataTask 中:

@Override
protected void onPostExecute(String sJson) {

   ....

    context.OnTaskCompleted(yourArray) // you just have to implement this method in ImageGridView activity
}