android - 异步任务下载图像然后将图像加载到水平画廊

Question

我正在使用 asynctask 下载图片，下载完成后，它应该将图片加载到我的水平图库中。是否可以？

现在我已经尝试过了，但它总是崩溃:

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

new downloadFile().execute();
gallery = (Gallery) findViewById(R.id.examplegallery);
gallery.setAdapter(new AddImgAdp(this));

    gallery.setOnItemClickListener(new OnItemClickListener() {
        public void onItemClick(AdapterView parent, View v, int position, long id) {
            // Displaying the position when the gallery item in clicked
            Toast.makeText(MainActivity.this, "Position=" + position, Toast.LENGTH_SHORT).show();
    }
    });

}

/**
     * Background Async Task to Load all product by making HTTP Request
     * */
    class downloadFile extends AsyncTask<String, String, String> {

        /**
         * getting all magazines from url
         * */
        protected String doInBackground(String... args) {
            URL myFileUrl = null;

        // Building Parameters
        List<NameValuePair> params = new ArrayList<NameValuePair>();
        // getting JSON string from URL
        JSONObject json = jParser.makeHttpRequest(url_login, "GET", params);

        // Check your log cat for JSON reponse
        Log.d("All Products: ", json.toString());

        try {
            // Checking for SUCCESS TAG
            int success = json.getInt(TAG_SUCCESS);

            if (success == 1) {
                // products found
                // Getting Array of Products
                mag = json.getJSONArray(TAG_MAGAZINE);

                for (int i = 0; i < mag.length(); i++) {
                    JSONObject c = mag.getJSONObject(i);

                    // Storing each json item in variable
                    String magLink = c.getString(TAG_MAGAZINE_URL);
                    String magThumb = c.getString(TAG_MAGAZINE_THUMBNAIL);
                    //String magazineIssue = c.getString(TAG_MAGAZINE_ISSUE);

                    urlList.add(magLink);
                    //urlList.add(magazineIssue);
                    thumbnailList.add(magThumb);

                    System.out.println(thumbnailList);
                }                   
            } 
            else {

            }
        } catch (JSONException e) {
            e.printStackTrace();
        }


        for (int i = 0; i < thumbnailList.size(); i ++)
        {
        thumbnail = thumbnailList.get(i).toString();
        Log.d("thumbnail", thumbnail);
        number = i;
            try {
                myFileUrl = new URL(thumbnail);    // RETRIEVE IMAGE URL
                }
             catch (MalformedURLException e) {
                e.printStackTrace();
            }
            try {
                HttpURLConnection conn = (HttpURLConnection) myFileUrl.openConnection();
                conn.setDoInput(true);
                conn.connect();
                InputStream in = conn.getInputStream();
                Log.i("im connected", "Download");
                bmImg = BitmapFactory.decodeStream(in);

                File filename;
                try {
                     // GET EXTERNAL STORAGE, SAVE FILE THERE
                    File storagePath = new File(Environment.getExternalStorageDirectory(),"Covers");
                    storagePath.mkdirs();

                    filename = new File(storagePath + "/photo"+number+".jpg");
                    FileOutputStream out = new FileOutputStream(filename);
                    bmImg.compress(Bitmap.CompressFormat.JPEG, 90, out);

                    out.flush();
                    out.close();
                    MediaStore.Images.Media.insertImage(getContentResolver(),filename.getAbsolutePath(), filename.getName(),
                            filename.getName());          



                 // displayImage();
                } catch (Exception e) {
                    e.printStackTrace();
                }   



            } catch (IOException e) {
                e.printStackTrace();
            }   

        }

            return null;
        }

        /**
     * After completing background task Dismiss the progress dialog
     * **/
    protected void onPostExecute() {    

        runOnUiThread(new Runnable() {
            public void run() {

              ArrayList<String>  mStringList= new ArrayList<String>();
              File strPath = new File(Environment.getExternalStorageDirectory() + "/Covers");
              int lists = strPath.listFiles().length; 
              Log.d("number of items in array ",String.valueOf(lists));

              File yourDir = new File(strPath, "");
              for (File f : yourDir.listFiles()) {
                  if (f.isFile())
                  {
                      String name = f.getName();
                      String v = strPath + "/" + name;
                      mStringList.add(v);
                  }
              }

              mImageIds = new String[mStringList.size()];
              mImageIds = mStringList.toArray(mImageIds);

              for(int a = 0; a < mImageIds.length ; a++){
                  Log.d("string is",(mImageIds[a]));
              }


            }



        });
    }
    }   

    public class AddImgAdp extends BaseAdapter {
        int GalItemBg;
        private Context cont;

        public AddImgAdp(Context c) {
            cont = c;
            TypedArray typArray = obtainStyledAttributes(R.styleable.GalleryTheme);
            GalItemBg = typArray.getResourceId(R.styleable.GalleryTheme_android_galleryItemBackground, 0);
            typArray.recycle();
            }
        public int getCount() {
            return mImageIds.length;
        }

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

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

        public View getView(int position, View convertView, ViewGroup parent) {
        ImageView imgView = new ImageView((Context) cont);

        imgView.setImageDrawable(Drawable.createFromPath(mImageIds[position]));

        // Fixing width & height for image to display
        imgView.setLayoutParams(new Gallery.LayoutParams(80, 70));
        imgView.setScaleType(ImageView.ScaleType.FIT_XY);
        imgView.setBackgroundResource(GalItemBg);

        return imgView;
        }
        }

}

这是我的 logcat 输出:

12-28 12:08:10.510: E/AndroidRuntime(5567): FATAL EXCEPTION: main
12-28 12:08:10.510: E/AndroidRuntime(5567): java.lang.RuntimeException: Unable to start activity ComponentInfo{com.example.horizontalviewing/com.example.horizontalviewing.MainActivity}: java.lang.NullPointerException
12-28 12:08:10.510: E/AndroidRuntime(5567):     at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:1978)
12-28 12:08:10.510: E/AndroidRuntime(5567):     at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2003)
12-28 12:08:10.510: E/AndroidRuntime(5567):     at android.app.ActivityThread.access$600(ActivityThread.java:123)
12-28 12:08:10.510: E/AndroidRuntime(5567):     at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1169)
12-28 12:08:10.510: E/AndroidRuntime(5567):     at android.os.Handler.dispatchMessage(Handler.java:99)
12-28 12:08:10.510: E/AndroidRuntime(5567):     at android.os.Looper.loop(Looper.java:137)
12-28 12:08:10.510: E/AndroidRuntime(5567):     at android.app.ActivityThread.main(ActivityThread.java:4446)
12-28 12:08:10.510: E/AndroidRuntime(5567):     at java.lang.reflect.Method.invokeNative(Native Method)
12-28 12:08:10.510: E/AndroidRuntime(5567):     at java.lang.reflect.Method.invoke(Method.java:511)
12-28 12:08:10.510: E/AndroidRuntime(5567):     at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:784)
12-28 12:08:10.510: E/AndroidRuntime(5567):     at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:551)
12-28 12:08:10.510: E/AndroidRuntime(5567):     at dalvik.system.NativeStart.main(Native Method)
12-28 12:08:10.510: E/AndroidRuntime(5567): Caused by: java.lang.NullPointerException
12-28 12:08:10.510: E/AndroidRuntime(5567):     at com.example.horizontalviewing.MainActivity$AddImgAdp.getCount(MainActivity.java:247)
12-28 12:08:10.510: E/AndroidRuntime(5567):     at android.widget.AbsSpinner.setAdapter(AbsSpinner.java:113)
12-28 12:08:10.510: E/AndroidRuntime(5567):     at com.example.horizontalviewing.MainActivity.onCreate(MainActivity.java:69)
12-28 12:08:10.510: E/AndroidRuntime(5567):     at android.app.Activity.performCreate(Activity.java:4465)
12-28 12:08:10.510: E/AndroidRuntime(5567):     at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1049)
12-28 12:08:10.510: E/AndroidRuntime(5567):     at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:1942)
12-28 12:08:10.510: E/AndroidRuntime(5567):     ... 11 more

Answer 1

getCount 方法中有一个空指针异常，因为您在执行后初始化之前初始化了适配器，要么将适配器创建移动到执行后代码中，要么首先初始化数组 mImageIds。