Android Webview cannot render the pdf sometimes and shows blank/white page instead

问题

Open the pdf in the webview using google docs
Open the same pdf or different pdf again and again.
Sometimes it will show the blank/white page in the android untill we refresh the webpage again for 1 or 2 times.

I have made the sample on the pdf. The link for the project is shown below:

https://github.com/gopalawasthi123/PdfWebView

Hope this will help you Better.

public void SetWebView(WebView webview,string externalUrl){
            webview.Tag = "webview";
            webview.Settings.JavaScriptEnabled = true;
            webview.Settings.SupportZoom ();
            webview.Settings.SetAppCacheEnabled(true);
            webview.Settings.DomStorageEnabled = true;
            webview.ZoomOut ();
            webview.ZoomIn ();
            webview.Settings.BuiltInZoomControls = true;
            webview.Settings.LoadWithOverviewMode = true;
            webview.Settings.UseWideViewPort = true;
            //webview.Settings.SetSupportZoom (true);
            webview.Settings.SetPluginState (WebSettings.PluginState.On);
            webview.Settings.GetPluginState ();
            if (externalUrl.StartsWith("http://") || externalUrl.StartsWith("https://"))
                webview.LoadUrl (externalUrl);
            webview.SetWebViewClient (new MonkeyWebViewClient (imgViewBack, imgViewForward, imgRefresh));
            webview.SetWebChromeClient (new WebChromeClient ());
        }

回答1:

You can reload the page until it displays the pdf in this way:

public void onPageFinished(WebView view, String url) {
if (view.getTitle().equals(""))
    view.reload();
}

回答2:

After testing second PDF URL file, WebView seems like that can not load large PDF file.

Reason:

WebView display HTML. The fact that this works at all is by a hack- google will convert simple PDFs into HTML. It doesn't seem like they support anything that big. Even if they did, I would expect loading a large page PDF converted to HTML would be so large I highly doubt you'd be able to load it without going OOM. Use an appropriate PDF library, make a real PDF rendering view, and make sure not to render more of the PDF at a time than you need (or else you'll go OOM anyway). In other words, don't rely on hacky solutions you never should have relied on in the first place.

Solution:

You should try alternatives like PDF.js running locally in your device, instead of a service like Google Docs preview.(Or download PDF first to local file path)

Put it in your assets folder and tweak the example:

wv.loadUrl("file:///android_asset/web/viewer.html");

Also, you can have Out Of Memory situations. An alternative to try is a native viewer like AndroidPdfViewer.

回答3:

We can solve the Problem in the two ways. 1. One is to use the Js.Pdf Plugin on the server end. It surely solve the problem but if we have multiple pdf's in the Fragment then it may cause the out of memory situations and app can crash. 2. Second option is we can recursively called the function to load webview. It works for me. Below is the code:

private void showPdf(final String imageString) {
pdfView.invalidate();
pdfView.getSettings().setJavaScriptEnabled(true);
pdfView.getSettings().setSupportZoom(true);
pdfView.loadUrl("http://docs.google.com/gview?embedded=true&url=" + imageString);
pdfView.setWebViewClient(new WebViewClient() {
    boolean checkhasOnPageStarted = false;

    @Override
    public void onPageStarted(WebView view, String url, Bitmap favicon) {
        checkhasOnPageStarted = true;
    }

    @Override
    public void onPageFinished(WebView view, String url) {
        if (checkhasOnPageStarted ) {
            pdfView.loadUrl(removePdfTopIcon);
        } else {
            showPdf(imageString);
        }
    }
});
}

来源：https://stackoverflow.com/questions/55829446/android-webview-cannot-render-the-pdf-sometimes-and-shows-blank-white-page-inste

标签

java

android

xamarin.android

android-webview