Implement a web application in Android.

README.md

Introduction

When develope the web app in Android, you have to customize all of the function by yourself; otherwise, they don't work.

1. WebViewClient
2. WebChromeClient
3. DownloadListener

We should implement three classes for handling various actions you need.

myActivity.java

public class MyActivity
{
    public static ValueCallback<Uri[]> mFilePathCallback;
    public static Uri imageUri = null;
    
    // Get the object from xml file.
    protected WebView wvClient;
    
    @Override
    public void onCreate(Bundle savedInstanceState)
    {
        super.onCreate(savedInstanceState);
        
        // Web view debug. 
        if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.KITKAT)
        {
            WebView.setWebContentsDebuggingEnabled(true);
        }
        
        // Add the Javascript interface for communication between this application and the server.
        this.wvClient.addJavascriptInterface(MyWebAppInterface, getString(R.string.app_name));
        // Setting Javascript can run on the website.
        this.wvClient.getSettings().setJavaScriptEnabled(true);
        // This is for playing a media on the webview.
        this.wvClient.setLayerType(View.LAYER_TYPE_HARDWARE, null);
        // Set a client for observe web site state.
        this.wvClient.setWebViewClient(new MyWebViewClient());
        // Set a chrome event for catching various events.
        this.wvClient.setWebChromeClient(new MyWebChromeClient());
        // Set a download listener for downloading a file.
        this.wvClient.setDownloadListener(new MyWebDownloadListener());
    }
    
    @Override
    protected void onActivityResult(int requestCode, int resultCode, Intent data)
    {
        super.onActivityResult(requestCode, resultCode, data);

        if (RESULT_OK == resultCode)
        {
            switch (requestCode)
            {
                case 5566:
                    Uri[] results;
                    // If there is not data, then we may have taken a photo
                    if (null == data.getData())
                    {
                        results = new Uri[] {imageUri};
                    }
                    else
                    {
                        results = new Uri[] {Uri.parse(data.getDataString())};
                    }

                    mFilePathCallback.onReceiveValue(results);
                    mFilePathCallback = null;
                    break;
                default:
                    break;
            }
        }
        else if (RESULT_CANCELED == resultCode)
        {
            mFilePathCallback.onReceiveValue(new Uri[] { });
            mFilePathCallback = null;
        }
    }
}

myDownloadListener.java

import android.webkit.DownloadListener;
import android.webkit.URLUtil;

public class MyDownloadListener implements DownloadListener
{
    @Override
    public void onDownloadStart(String url, String userAgent, String contentDisposition, String mimetype, long contentLength)
    {
        String filename = URLUtil.guessFileName(url, contentDisposition, mimetype);
        DownloadManager.Request request = new DownloadManager.Request(Uri.parse(url));
        request.allowScanningByMediaScanner();
        request.setNotificationVisibility(DownloadManager.Request.VISIBILITY_VISIBLE_NOTIFY_COMPLETED);
        request.setDestinationInExternalPublicDir(Environment.DIRECTORY_DOWNLOADS, filename);

        ((DownloadManager) tantraView.context().getSystemService(DOWNLOAD_SERVICE)).enqueue(request);
        tantraView.showToastMsg("Start to download " + filename + "...", Toast.LENGTH_SHORT);
    }
}

myWebChromeClient.java

public class MyWebChromeClient extends WebChromeClient
{
    // From javascript alert() function.
    @Override
    public boolean onJsAlert(WebView view, String url, String message, JsResult result)
    {
        new AlertDialog.Builder(context(), R.style.MyAlertDialogStyle).setTitle("title")
                                                                      .setMessage(message)
                                                                      .setPositiveButton("ok", (dialog, which) -> result.confirm())
                                                                      .setCancelable(false)
                                                                      .create()
                                                                      .show();
        return true;
    }

    // From javascript confirm() function.
    @Override
    public boolean onJsConfirm(WebView view, String url, String message, JsResult result)
    {
        new AlertDialog.Builder(context(), R.style.MyAlertDialogStyle).setTitle("title")
                                                                      .setMessage(message)
                                                                      .setPositiveButton("ok", (dialog, which) -> result.confirm())
                                                                      .setNegativeButton("cancel", (dialog, which) -> result.cancel())
                                                                      .setCancelable(false)
                                                                      .create()
                                                                      .show();
        return true;
    }

    @Override
    public boolean onShowFileChooser(WebView webView, ValueCallback<Uri[]> filePathCallback, FileChooserParams fileChooserParams)
    {
        // Directlt use this callback in anywhere.
        if (mFilePathCallback != null)
        {
            mFilePathCallback.onReceiveValue(new Uri[] { });
            mFilePathCallback = null;
        }
        mFilePathCallback = filePathCallback;

        // Create camera intent for taking a picture.
        Intent takePictureIntent = new Intent(MediaStore.ACTION_IMAGE_CAPTURE);
        File file = new File(Environment.getExternalStorageDirectory() + File.separator + "image.jpg");
        if (file.exists())
        {
            file.delete();
            file = new File(Environment.getExternalStorageDirectory() + File.separator + "image.jpg");
        }
        imageUri = Uri.fromFile(file);
        takePictureIntent.putExtra(MediaStore.EXTRA_OUTPUT, imageUri);

        // Create intent for picking any data type of file.
        Intent contentSelectionIntent = new Intent(Intent.ACTION_GET_CONTENT);
        contentSelectionIntent.addCategory(Intent.CATEGORY_OPENABLE);
        contentSelectionIntent.setType("*/*");

        // Create intent for picking a photo from the gallery
        Intent photosSelectionIntent = new Intent(Intent.ACTION_PICK, MediaStore.Images.Media.EXTERNAL_CONTENT_URI);

        Intent chooserIntent = new Intent(Intent.ACTION_CHOOSER);
        chooserIntent.putExtra(Intent.EXTRA_TITLE, "Choose an action");
        chooserIntent.putExtra(Intent.EXTRA_INITIAL_INTENTS, new Intent[] {takePictureIntent, photosSelectionIntent});
        chooserIntent.putExtra(Intent.EXTRA_INTENT, contentSelectionIntent);

        startActivityForResult(chooserIntent, 5566);

        return true;
    }
}

myWebViewClient.java

public class MyWebViewClient extends WebViewClient
{
    @Override
    public boolean shouldOverrideUrlLoading(WebView view, String url)
    {
        return false;
    }

    @Override
    public void onPageStarted(WebView view, String url, Bitmap favicon)
    {
        super.onPageStarted(view, url, favicon);
    }

    @Override
    public void onReceivedError(WebView view, WebResourceRequest request, WebResourceError error)
    {
        super.onReceivedError(view, request, error);
    }

    @Override
    public void onReceivedHttpError(WebView view, WebResourceRequest request, WebResourceResponse errorResponse)
    {
        super.onReceivedHttpError(view, request, errorResponse);
    }

    @Override
    public void onReceivedSslError(WebView view, SslErrorHandler handler, SslError error)
    {
        super.onReceivedSslError(view, handler, error);
    }

    @Override
    public void onPageFinished(WebView view, String url)
    {
        super.onPageFinished(view, url);
    }
}