android - ViewPager 使用了错误的条目

Question

我有以下类(class)来展示一些图像......我已经实现了将图像下载到 SD 卡的功能。如果我通过它们，一切都很好(显示图像 + 标题)，但如果我从某个图像开始下载，使用另一个 url(另一个图像的)，所以我以某种方式认为我的 ViewPager 没有正确更新或其他东西。

这是我的课:

public class ImagePagerActivity extends BaseActivity {

private ViewPager pager;

LinearLayout buttonBar;
TextView txtTitle;

String urlOfImageToDownload;

public static final int DIALOG_DOWNLOAD_PROGRESS = 0;
private ProgressDialog mProgressDialog;

private static DisplayImageOptions options;

ImageView imageView;

public void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);

    setContentView(R.layout.ac_image_pager);
    Bundle bundle = getIntent().getExtras();
    String[] imageUrls = bundle.getStringArray(Extra.IMAGES);
    String[] imageTitles = bundle.getStringArray(Extra.TITLES);
    int pagerPosition = bundle.getInt(Extra.IMAGE_POSITION, 0);

    options = new DisplayImageOptions.Builder()
            .cacheOnDisc().showImageForEmptyUri(R.drawable.no_image)
            .imageScaleType(ImageScaleType.IN_SAMPLE_POWER_OF_2)
            .build();

    pager = (ViewPager) findViewById(R.id.pager);
    pager.setAdapter(new ImagePagerAdapter(imageUrls, imageTitles));
    pager.setCurrentItem(pagerPosition);
}

@Override
public boolean onPrepareOptionsMenu(Menu menu) {
    if (imageView.getDrawable() == null)
        menu.getItem(0).setEnabled(false);
    return true;
}

public boolean onCreateOptionsMenu(Menu menu) {
    menu.add(0, 0, 0,
            getString(R.string.save_image)).setIcon(android.R.drawable.ic_menu_save);
    return true;
}

public boolean onOptionsItemSelected(MenuItem item) {
    switch (item.getItemId()) {
        case 0:
            Random randomGenerator = new Random();
            int randomInt = 0;
            for (int idx = 1; idx <= 10; ++idx) {
                randomInt = randomGenerator.nextInt(100000);
            }

            imageView.setDrawingCacheEnabled(true);
            Bitmap b = imageView.getDrawingCache();
            try {
                b.compress(CompressFormat.JPEG, 100,
                        new
                        FileOutputStream(Environment.getExternalStorageDirectory()
                                .getPath() + "/DCIM/image" + randomInt + ".jpg"));
                Crouton.makeText(ImagePagerActivity.this,
                        "Bild erfolgreich gespeichert",
                        Style.INFO)
                        .show();
            } catch (FileNotFoundException e) {
                Crouton.makeText(ImagePagerActivity.this,
                        "Fehler beim speichern von Datei",
                        Style.ALERT)
                        .show();
            }

            startDownload();

            return true;
    }
    return false;
}

private void startDownload() {
    String url = urlOfImageToDownload;
    Log.e(MainActivity.LOG_TAG, "url=" + urlOfImageToDownload);
    new DownloadFileAsync().execute(url);
}

@Override
protected Dialog onCreateDialog(int id) {
    switch (id) {
        case DIALOG_DOWNLOAD_PROGRESS:
            mProgressDialog = new ProgressDialog(this);
            mProgressDialog.setMessage(getString(R.string.downloading_image));
            mProgressDialog.setProgressStyle(ProgressDialog.STYLE_HORIZONTAL);
            mProgressDialog.setCancelable(false);
            mProgressDialog.show();
            return mProgressDialog;
        default:
            return null;
    }
}

@Override
protected void onStop() {
    imageLoader.stop();
    super.onStop();
}

private class ImagePagerAdapter extends PagerAdapter {

    private String[] images;
    private String[] titles;
    private LayoutInflater inflater;

    ImagePagerAdapter(String[] images, String[] imageTitles) {
        this.images = images;
        this.titles = imageTitles;
        inflater = getLayoutInflater();
    }

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

    @Override
    public void finishUpdate(View container) {
    }

    @Override
    public int getCount() {
        return images.length;
    }

    @Override
    public Object instantiateItem(View view, int position) {
        final FrameLayout imageLayout = (FrameLayout) inflater.inflate(
                R.layout.item_pager_image, null);
        imageView = (ImageView) imageLayout
                .findViewById(R.id.image);
        final ProgressBar spinner = (ProgressBar) imageLayout
                .findViewById(R.id.loading);
        txtTitle = (TextView) imageLayout.findViewById(R.id.txtTitle);

        urlOfImageToDownload = images[position];

        buttonBar = (LinearLayout) imageLayout.findViewById(R.id.buttonBar);

        txtTitle.setText(titles[position]);

        imageLoader.displayImage(images[position], imageView, options,
                new ImageLoadingListener() {
                    @Override
                    public void onLoadingStarted() {
                        spinner.setVisibility(View.VISIBLE);
                    }

                    @Override
                    public void onLoadingFailed(FailReason failReason) {
                        switch (failReason) {
                            case IO_ERROR:
                                break;
                            case OUT_OF_MEMORY:
                                break;
                            case UNKNOWN:
                                break;
                        }

                        spinner.setVisibility(View.GONE);
                        imageView.setImageResource(android.R.drawable.ic_delete);
                    }

                    @Override
                    public void onLoadingComplete(Bitmap bm) {
                        spinner.setVisibility(View.GONE);
                    }

                    @Override
                    public void onLoadingCancelled() {
                        spinner.setVisibility(View.GONE);
                    }
                });

        ((ViewPager) 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;
    }

    @Override
    public void startUpdate(View container) {
    }

}

class DownloadFileAsync extends AsyncTask<String, String, String> {

    @SuppressWarnings("deprecation")
    @Override
    protected void onPreExecute() {
        super.onPreExecute();
        showDialog(DIALOG_DOWNLOAD_PROGRESS);
    }

    @Override
    protected String doInBackground(String... aurl) {
        int count;

        try {

            URL url = new URL(aurl[0]);
            URLConnection conexion = url.openConnection();
            conexion.connect();

            int lenghtOfFile = conexion.getContentLength();

            Random rand = new Random();
            int randomNumber = rand.nextInt(100000);

            InputStream input = new BufferedInputStream(url.openStream());
            OutputStream output = new FileOutputStream(
                    "sdcard/nature_" + randomNumber + ".jpg");

            byte data[] = new byte[1024];

            long total = 0;

            while ((count = input.read(data)) != -1) {
                total += count;
                publishProgress("" + (int) ((total * 100) / lenghtOfFile));
                output.write(data, 0, count);
            }

            output.flush();
            output.close();
            input.close();
        } catch (Exception e) {
        }
        return null;

    }

    protected void onProgressUpdate(String... progress) {
        mProgressDialog.setProgress(Integer.parseInt(progress[0]));
    }

    @Override
    protected void onPostExecute(String unused) {
        dismissDialog(DIALOG_DOWNLOAD_PROGRESS);
        Crouton.makeText(ImagePagerActivity.this,
                getString(R.string.image_saved),
                Style.CONFIRM)
                .show();
    }
  }
}

感谢您的帮助!

Answer 1

问题:

用户第一次在 ViewPager 中查看图像时，将调用该图像的 instantiateItem(..) 并将字段 urlOfImagetoDownload 设置为正确的 URL:

urlOfImageToDownload = images[position];

但是，如果用户现在返回他之前看到的已经实例化的图像，instantiateItem(...) 将不会被调用并且urlOfImageToDownload 将包含错误的 URL(上一张图片的)。

解决方法:

您可以使用 ViewPager#getCurrentItem() 检索当前图像的索引，然后将该索引与 images[] 一起使用以获得正确的 URL 当用户点击下载时。