PagerAdapter notifyDataSetChanged

Question

应用程序的PagerAdapter更改了适配器的内容，而没有调用PagerAdapter#notifyDataSetChanged！预期的适配器项目数：0，找到的：3 Pager  ID

我的Android项目中出现此错误。在这里，我为此使用视图寻呼机。我从网络服务获得图像作为字节码。

public class MainActivity extends AppCompatActivity {

    private String TAG = MainActivity.class.getSimpleName();
    private ProgressDialog pDialog;

    ArrayList<String> alListImage;

    private static ViewPager mPager;
    private static int currentPage = 0;
    private static int NUM_PAGES = 0;
    private static final Integer[] IMAGES= {R.drawable.one,R.drawable.two,R.drawable.three,R.drawable.one,R.drawable.two,R.drawable.three,};
    private ArrayList<String> ImagesArray = new ArrayList<String>();
    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        alListImage=new ArrayList<String>();
        new GetContacts().execute();
        init();
    }

    private void init() {
        mPager = (ViewPager) findViewById(R.id.pager);
        mPager.setAdapter(new Adapter(MainActivity.this,alListImage));

        // Auto start of viewpager
        final Handler handler = new Handler();
        final Runnable Update = new Runnable() {
            public void run() {
                if (currentPage == alListImage.size()) {
                    currentPage = 0;
                }
                mPager.setCurrentItem(currentPage++, true);
            }
        };
        Timer swipeTimer = new Timer();
        swipeTimer.schedule(new TimerTask() {
            @Override
            public void run() {
                handler.post(Update);
            }
        }, 3000, 3000);
    }

    private class GetContacts extends AsyncTask<Void, Void, Void> {

        @Override
        protected void onPreExecute() {
            super.onPreExecute();
            // Showing progress dialog
            pDialog = new ProgressDialog(MainActivity.this);
            pDialog.setMessage("Please wait...");
            pDialog.setCancelable(false);
            pDialog.show();
        }

        @Override
        protected Void doInBackground(Void... arg0) {
            HttpHandler sh = new HttpHandler();

            String url = "http://webapirestro.appro.com.sg/api/Category/GetCategory?CompanyId=771416A2-56C6-46A5-8EB5-655E4361A22A";
            //String url = "http://webapirestro.appro.com.sg/api/TvImage/Gettv_image?CompanyId=771416A2-56C6-46A5-8EB5-655E4361A22A";

            // Making a request to URL and getting response
            final String jsonStr = sh.makeServiceCall(url);
            if (jsonStr != null) {
                try {
                    JSONObject jsonObj = new JSONObject(jsonStr);

                    // Getting JSON Array node
                    JSONArray ListData = jsonObj.getJSONArray("ListData");

                    // Looping through All Contacts
                    for (int i = 0; i < ListData.length(); i++) {
                        JSONObject c = ListData.getJSONObject(i);

                        String sImageByte = c.getString("ImageByte");
                        String sCatname = c.getString("CategoryName");

                        if(sImageByte.equals(false)){
                            sImageByte = "ABC";
                        }

                        // Adding contact to contact list
                        alListImage.add(sImageByte);
                    }
                }
                catch (final JSONException e) {
                    Log.e(TAG, "JSON parsing error: " + e.getMessage());
                    runOnUiThread(new Runnable() {
                        @Override
                        public void run() {
                            Toast.makeText(getApplicationContext(),
                                    "Json parsing error: " + e.getMessage(),
                                    Toast.LENGTH_LONG)
                                    .show();
                        }
                    });

                }
            }
            else {
                Log.e(TAG, "Couldn't get json from server.");
                runOnUiThread(new Runnable() {
                    @Override
                    public void run() {
                        Toast.makeText(getApplicationContext(),
                                "Couldn't get json from server. Check LogCat for possible errors!",
                                Toast.LENGTH_LONG)
                                .show();
                    }
                });
            }
            return null;
        }

        @Override
        protected void onPostExecute(Void result) {
            super.onPostExecute(result);
            // Dismiss the progress dialog
            if (pDialog.isShowing())
                pDialog.dismiss();
            /**
             * Updating parsed JSON data into ListView
             * */
        }
    }
}

public class Adapter extends PagerAdapter {
    private ArrayList<String> IMAGES;
    private LayoutInflater inflater;
    private Context context;

    public Adapter(Context context,ArrayList<String> IMAGES) {
        this.context = context;
        this.IMAGES=IMAGES;
        inflater = LayoutInflater.from(context);
        notifyDataSetChanged();
    }

    @Override
    public void destroyItem(ViewGroup container, int position, Object object) {
        container.removeView((View) object);
    }

    @Override
    public int getCount() {

        return IMAGES.size();
    }

    @Override
    public Object instantiateItem(ViewGroup view, int position) {
        View imageLayout = inflater.inflate(R.layout.single_pager, view, false);

        assert imageLayout != null;
        final ImageView imageView = (ImageView) imageLayout
                                      .findViewById(R.id.image);
        for(int i=0;i<IMAGES.size();i++) {
            byte[] decode = Base64.decode(IMAGES.get(i), Base64.DEFAULT);
            Bitmap bitmap = BitmapFactory.decodeByteArray(decode, 0, decode.length);

            imageView.setImageBitmap(bitmap);
        }

        view.addView(imageLayout, 0);

        return imageLayout;
    }

    @Override
    public boolean isViewFromObject(View view, Object object) {
        return view.equals(object);
    }

    @Override
    public void restoreState(Parcelable state, ClassLoader loader) {
    }

    @Override
    public Parcelable saveState() {
        return null;
    }
}

Answer 1

GetContacts是一个AsyncTask，在其doInBackground方法中，您输入了以下行：

alListImage.add(sImageByte); // This makes the adapter item number equal to 3

为避免这种情况，您可以在一段时间后使用postDelayed执行GetContacts。