WebView无法加载URL中的PDF，提示“Preview not Available”求解决

Hey there! Let's work through those WebView PDF problems you're hitting. Android's default WebView doesn't natively render PDF files, which is why you're seeing that "Preview not Available" message. Here are two solid solutions to get it working:

Solution 1: Use Google Docs Online Preview (Quick & Easy) #

This method leverages Google's PDF rendering service to display the file in WebView. It's great if your users have a stable internet connection.

Step-by-Step Implementation: #

1. Modify your loadUrl() method to wrap the PDF URL with the Google Docs preview link. Make sure to URL-encode the original PDF address to handle special characters.
2. Enable necessary WebView settings to ensure the preview loads properly.

Here's the updated code:

private void loadUrl() {
    String reportStatus = caseList.get(position).getReportStatus();
    // Replace this with your actual PDF URL from caseList
    String pdfUrl = caseList.get(position).getYourPdfUrlKey(); 

    WebSettings webSettings = mWebView.getSettings();
    webSettings.setJavaScriptEnabled(true);
    webSettings.setAllowFileAccess(true);
    webSettings.setDomStorageEnabled(true);
    webSettings.setLoadWithOverviewMode(true);
    webSettings.setUseWideViewPort(true);

    mWebView.setWebViewClient(new WebViewClient() {
        @Override
        public boolean shouldOverrideUrlLoading(WebView view, String url) {
            // Check if the URL points to a PDF
            if (url.toLowerCase().endsWith(".pdf")) {
                // Encode the URL and wrap with Google Docs preview
                String encodedPdfUrl = Uri.encode(url);
                String googlePreviewUrl = "https://docs.google.com/gview?embedded=true&url=" + encodedPdfUrl;
                view.loadUrl(googlePreviewUrl);
                return true;
            }
            view.loadUrl(url);
            return true;
        }

        @Override
        public void onPageFinished(WebView view, final String url) {
            // Add any post-load logic here (e.g., hide loading spinner)
        }

        // Optional: Handle loading errors gracefully
        @Override
        public void onReceivedError(WebView view, WebResourceRequest request, WebResourceError error) {
            super.onReceivedError(view, request, error);
            Toast.makeText(view.getContext(), "Failed to load PDF: " + error.getDescription(), Toast.LENGTH_SHORT).show();
        }
    });

    // Load the PDF if report status is valid
    if (!TextUtils.isEmpty(reportStatus)) {
        String encodedPdfUrl = Uri.encode(pdfUrl);
        String googlePreviewUrl = "https://docs.google.com/gview?embedded=true&url=" + encodedPdfUrl;
        mWebView.loadUrl(googlePreviewUrl);
    }
}

Solution 2: Use a Local PDF Rendering Library (Offline Support) #

If you need offline access or don't want to rely on Google's service, use a dedicated PDF library like AndroidPdfViewer. This gives you full control over rendering.

Step-by-Step Implementation: #

1. Add the library dependency to your app-level build.gradle file:

dependencies {
    implementation 'com.github.barteksc:android-pdf-viewer:3.2.0-beta.1'
}

2. Add the PDFView to your layout:

<com.github.barteksc.pdfviewer.PDFView
    android:id="@+id/pdfView"
    android:layout_width="match_parent"
    android:layout_height="match_parent"/>

3. Load the PDF in your activity/fragment:

// Initialize the PDFView
PDFView pdfView = findViewById(R.id.pdfView);
String pdfUrl = caseList.get(position).getYourPdfUrlKey();

// Load from URL (handles downloading internally)
pdfView.fromUrl(pdfUrl)
    .enableSwipe(true) // Allow swiping between pages
    .swipeHorizontal(false) // Vertical swipe by default
    .enableDoubletap(true) // Zoom with double tap
    .defaultPage(0) // Start at first page
    .onLoad(nbPages -> {
        // PDF loaded successfully
    })
    .onError(throwable -> {
        Toast.makeText(this, "Failed to load PDF", Toast.LENGTH_SHORT).show();
    })
    .load();

Key Checks to Ensure Success: #

• Verify the PDF URL: Make sure the URL works in a regular browser (no broken links, login walls, or expired certificates).
• Permissions: Ensure your app has the INTERNET permission in AndroidManifest.xml for loading network PDFs:

<uses-permission android:name="android.permission.INTERNET"/>

• SSL Certificates: If loading an HTTPS PDF, ensure the server's SSL certificate is valid (self-signed certs may need extra handling).

内容的提问来源于stack exchange，提问作者Shanmuga M