Using images from apk expansion file in android webview

Question

I have an android app that displays maps. The maps are hi-res images sliced to 100 tiles per map to maintain resolution. I currently have each map in a separate folder in my assets folder. As this makes my apk huge, I want to move these images to my main apk expansion file. Currently I am displaying the images in a webview using the following code to stitch the tiles together in the webview:

class ShowMapTask extends AsyncTask<String, Void, String> {

    @Override
    protected String doInBackground(String... maps) {
        String html = "<html><table cellpadding=\"0\" border=\"0\" cellspacing=\"0.0\">";
        for (int i = 0; i < 10; i++) {
            html += "<tr>";
            for (int j = 0; j < 10; j++)
                html += "<td><img src=\"maps/" + maps[0] + "/slice_" + i
                        + "_" + j + ".png\"></td>";
            html += "</tr>";
        }
        return html + "</table></html>";
    }

    @Override
    protected void onPostExecute(String result) {
        WebView wv = (WebView) context.findViewById(R.id.webView);
        wv.getSettings().setSupportZoom(true);
        wv.getSettings().setBuiltInZoomControls(true);
        wv.getSettings().setUseWideViewPort(true);
        wv.getSettings().setLoadWithOverviewMode(true);
        wv.loadDataWithBaseURL("file:///android_asset/", result,
                "text/html", "utf-8", null);
        super.onPostExecute(result);
    }
}

How do I migrate to the apk expansion file? Is it possible to use the images without having the unzip the obb to the sdcard?

Did you ever solve this problem? I have a solution for API 11 and greater, see http://stackoverflow.com/questions/13073594/how-to-load-image-from-expansion-file-into-webview I am using webview.loadUrl but I have verified it works the same with webview.loadDataWithBaseURL Still need a solution for API 10 though — Chris Fawcett, Oct 30 '12 at 16:36
Couldn’t solve this. I am currently extracting the obb to the sdcard and using the images from there. — Javed, Nov 28 '12 at 14:50

score 3 · Answer 1 · edited Dec 15 '14 at 14:02

I'm going to try responding with a new answer since my original answer was downgraded to a comment. I'm not sure why but I do have a solutions now for API 10 and under as well as API 11 and over. I'll post code to clarify.

For API 11 and over simply override ShouldInterceptRequest in your webview client,

For API 10 and under use this http listener, http://elonen.iki.fi/code/nanohttpd/,

Putting the two approaches together, the relevant pieces of code for me were:

final String assetPrefix = "file:///android_asset/";
final String httpPrefix = "http://localhost:8001";

// for me this part is in onCreateView after the webview settings bit...
{

    if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.HONEYCOMB)
        webView.setWebViewClient(new HoneyCombWebViewClient());
    else
        webView.setWebViewClient(new MyWebViewClient());    

    webViewLoadUrl();
}

private void webViewLoadUrl() {
    if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.HONEYCOMB) {

        curURL = assetPrefix + curFileName;


        webView.loadUrl(curURL);
    }
    else
    {
        curURL = httpPrefix + '/' + curFileName;

        String str = assetFileToString(curFileName);        
        webView.loadDataWithBaseURL(httpPrefix, str, "text/html", "UTF-8", null);    
    }
}

// then for the WebViewClient
private class HoneyCombWebViewClient extends MyWebViewClient {

    public WebResourceResponse shouldInterceptRequest(WebView view, String url)
    {
                    // remove the asset prefix from the url
        String fileName = url.substring(assetPrefix.length() - 1);

                    // ExpansionFiles is the pointer to your ZipResourceFile
        InputStream inputStream = ExpansionFiles.getWebResource(fileName);

        if (url.endsWith("jpg") || url.endsWith("png"))
            return new WebResourceResponse("image/*", "base64", inputStream);

        return super.shouldInterceptRequest(view, url);
    }
}

private class MyWebViewClient extends WebViewClient {
    @Override
    public boolean shouldOverrideUrlLoading(WebView view, String url) {

            else if (url.startsWith(httpPrefix)) {

            curURL = url;

            String str = assetFileToString(url.substring(httpPrefix.length() + 1));

            webView.loadDataWithBaseURL(httpPrefix, str, "text/html", "UTF-8", null); 
            return true;
        }
        else if (url.startsWith(assetPrefix)){
            curURL = url;

            view.loadUrl(url);
            return true;        
        }
        // else.....
    }
}

Finally, to use NanoHTTPD, find the methods serve and have it return the input stream to your file from the expansion file:

public Response serve( String uri, String method, Properties header, Properties parms, Properties files )
{
    InputStream data = ExpansionFiles.getWebResource(uri);

    String mimeType;
    if (uri.endsWith("jpg") || uri.endsWith("png"))
        mimeType = "base64";
    else if (uri.endsWith("css"))
        mimeType = "text/css";
    else if (uri.endsWith("js"))
        mimeType = "text/javascript";
    else
        mimeType = "text/html";

    return new Response( HTTP_OK, mimeType, data );
}

Put in a call to the constructor somewhere at your toplevel:

if (Build.VERSION.SDK_INT < Build.VERSION_CODES.HONEYCOMB) {
    // this for loading images from expansion file under webview in API 10
    try
    {
        webServer = new NanoHTTPD(8001, new File("."));
    }
    catch( IOException ioe )
    {
        System.err.println( "Couldn't start server:\n" + ioe );
        System.exit( -1 );
    }
}

Oh, and you'll need to remove the main method from NanoHTTPD

I hope you find this helpful. It was a long and painful process for me....

NanoHTTPD has deprecated serve(String, String, Properties...) in favour of serve(IHTTPSession), but you can get at all the properties just the same - IHTTPSession.getUri(), etc. — AndyC, Sep 23 '13 at 18:41

score 1 · Answer 2 · answered Nov 05 '13 at 16:06

1

It is a good alternative to use JOBB tools to pack expansion file and use StorageManager to mount it. After that the files inside expansion file should be accessible as regular files in the file system. The unpacking of expansion file is not needed in this case.

answered Nov 05 '13 at 16:06

Aleksei

1,207
1
13
16

Thanks! I thought this was a great approach. I wrote up a blog post that described how I implemented it: http://saveme-dot-txt.blogspot.com/2016/06/setting-up-google-play-expansion-file.html – Mike M Jun 14 '16 at 14:08

Using images from apk expansion file in android webview

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