如何在 Android ImageView 中显示 PDF 文件

Question

是否可以在 Android 视图中显示巨大的 pdf 文件？

我只需要能够显示它，通过捏合和缩放以及这些天在 ImageViews 中实现的其他正常功能。

Answer 1

共有三个开源库，它们组合在一起，可以满足您的需求。所有都获得了 Apache V2（或 Beer-Ware 许可证）的许可！

请注意，需要 V21 或更高版本。但如果需要，您可以使用 if 语句和 Intent 作为后备。

1. Subsampling-scale-image-view：“Android 的自定义图像视图，专为照片库和显示大图而设计”
2. Subsampling-pdf-decoder: "用于二次采样比例图像视图的 pdf 解码器库"
3. VerticalViewPager：这是可选的，但我认为您想要上下滚动而不是左右滚动。

如何实现这一点的例子，在解码器库的示例中给出。

1.) Gradle 依赖项

repositories {
  mavenCentral()
  jcenter()

  //decoder library, will soon be on jcenter 
  maven { url 'https://dl.bintray.com/n42/maven'} 
}

dependencies {
  compile 'com.davemorrissey.labs:subsampling-scale-image-view:3.5.0'
  compile 'com.github.castorflex.verticalviewpager:library:19.0.1'
  compile 'de.number42:subsampling-pdf-decoder:0.1.0@aar'
}

2.) 实现一个PagerAdapter，你可以使用这个

public class PDFPagerAdapter extends PagerAdapter {
  /**
   * context for the view
   */
  private Context context;

  /**
   * pdf file to show
   */
  private File file;

  /**
   * file descriptor of the PDF
   */
  private ParcelFileDescriptor mFileDescriptor;

  /**
   * this scale sets the size of the {@link PdfRenderer.Page} in the {@link
   * PDFRegionDecoder}.
   * Since it rescales the picture, it also sets the possible zoom level.
   */
  private float scale;

  /**
   * this renderer is only used to count the pages
   */
  private PdfRenderer renderer;

  /**
   * @param file the pdf file
   */
  public PDFPagerAdapter(Context context, File file) {
    super();
    this.context = context;
    this.file = file;
    this.scale = 8;
    try {
      mFileDescriptor = ParcelFileDescriptor.open(file, ParcelFileDescriptor.MODE_READ_ONLY);
      renderer = new PdfRenderer(mFileDescriptor);
    } catch (IOException e) {
      throw new RuntimeException(e);
    }
  }

  /**
   * Instantiate an item. Therefor a {@link SubsamplingScaleImageView} with special decoders is
   * initialized and rendered.
   *
   * @param container isn't used here
   * @param position the current pdf page position
   */
  public Object instantiateItem(ViewGroup container, int position) {

    SubsamplingScaleImageView imageView = new SubsamplingScaleImageView(context);

    // the smaller this number, the smaller the chance to get an "outOfMemoryException"
    // still, values lower than 100 really do affect the quality of the pdf picture
    int minimumTileDpi = 120;
    imageView.setMinimumTileDpi(minimumTileDpi);

    //sets the PDFDecoder for the imageView
    imageView.setBitmapDecoderFactory(() -> new PDFDecoder(position, file, scale));

    //sets the PDFRegionDecoder for the imageView
    imageView.setRegionDecoderFactory(() -> new PDFRegionDecoder(position, file, scale));

    ImageSource source = ImageSource.uri(file.getAbsolutePath());

    imageView.setImage(source);

    container.addView(imageView);
    return imageView;
  }

  /**
   * gets the pdf site count
   *
   * @return pdf site count
   */
  public int getCount() {
    return renderer.getPageCount();
  }

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

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

3.) 为 VerticalViewPager 启动和设置适配器

VerticalViewPager pager = (VerticalViewPager) findViewById(R.id.pager);
File pdfFile = ....

PDFPagerAdapter pagerAdapter = new PDFPagerAdapter(this,pdfFile);
pager.setAdapter(pagerAdapter);

Answer 2

您可以为此使用 webview，并且很容易实现。这样做

 @SuppressLint("NewApi")
    private void startWebView(String url) {

        // Create new webview Client to show progress dialog
        // When opening a url or click on link
        // Javascript inabled on webview
        web.getSettings().setJavaScriptEnabled(true);
        web.getSettings().setBuiltInZoomControls(true);
        web.getSettings().setDisplayZoomControls(false);
        web.getSettings().setLoadWithOverviewMode(true);
        web.getSettings().setUseWideViewPort(true);

        web.getSettings().setDomStorageEnabled(true);
        web.setWebChromeClient(new WebChromeClient());
//        web.getSettings().setPluginState(WebSettings.PluginState.ON);
        web.setWebViewClient(new WebViewClient() {
            ProgressDialog progressDialog;

            // If you will not use this method url links are opeen in new brower
            // not in webview
            public boolean shouldOverrideUrlLoading(WebView view, String url) {
                view.loadUrl(url);
                return true;
            }
            @SuppressWarnings("deprecation")
            @Override
            public void onReceivedError(WebView view, int errorCode, String description, final String failingUrl) {
                web.loadUrl("about:blank");


            }

            // Show loader on url load
            public void onLoadResource(WebView view, String url) {
               /* if (progressDialog == null) {
                    // in standard case YourActivity.this
                    if (getActivity() != null) {
                        progressDialog = new ProgressDialog(getActivity());
                        progressDialog.setMessage("Loading...");
                        progressDialog.show();
                    }

                }*/

            }

            public void onPageFinished(WebView view, String url) {
                try {
                    setProgressBar(false);
                } catch (Exception e) {

                }
            }

        });


        // Load url in webview
        web.loadUrl(url);

    }