Capture image generated by Google Charts API

Previous posts show how to "Display Google Charts (pie chart) on Android WebView" and "More Google Charts examples on Android WebView". To capture the PNG image of a chart, we can use the getImageURI() method, it return a string in "data:image/png;base64,..." format.


We can pass this string to Android code, decode and generate bitmap. To decode string in "data:image/png;base64,..." format, to Bitmap, we can use the code:

 private Bitmap decodeBase64PNG(String src){

  String imageDataBytes = src.substring(src.indexOf(",") + 1);
  
  InputStream stream = 
   new ByteArrayInputStream(
    Base64.decode(imageDataBytes.getBytes(), 
    Base64.DEFAULT));
  
     Bitmap bitmap = BitmapFactory.decodeStream(stream);
     return bitmap;
 }

For MainActivity.java, activity_main.xml and AndroidManifest.xml, refer to last post "Display Google Charts (pie chart) on Android WebView".

Other files modify from last post "More Google Charts examples on Android WebView".

Modify layout_webchart.xml to add a Button to Capture the image.

    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:orientation="vertical" >
    
            android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_gravity="center_horizontal"
        android:autoLink="web"
        android:text="http://picturedmagazine.blogspot.com/"
        android:textStyle="bold" />
    
            android:id="@+id/spcharts"
        android:layout_width="match_parent"
        android:layout_height="wrap_content" />
    
            android:id="@+id/capture"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:text="Capture" />
    
            android:id="@+id/web"
        android:layout_width="match_parent"
        android:layout_height="match_parent"/>

ShowWebChartActivity.java

package com.example.androidwebchart;

import java.io.ByteArrayInputStream;
import java.io.InputStream;
import java.util.ArrayList;
import java.util.List;

import android.annotation.SuppressLint;
import android.app.Dialog;
import android.content.Intent;
import android.graphics.Bitmap;
import android.graphics.BitmapFactory;
import android.os.Bundle;
import android.support.v7.app.ActionBarActivity;
import android.util.Base64;
import android.view.View;
import android.view.View.OnClickListener;
import android.view.ViewGroup.LayoutParams;
import android.webkit.JavascriptInterface;
import android.webkit.WebView;
import android.widget.AdapterView;
import android.widget.AdapterView.OnItemSelectedListener;
import android.widget.ArrayAdapter;
import android.widget.Button;
import android.widget.ImageView;
import android.widget.Spinner;
import android.widget.Toast;

@SuppressLint("SetJavaScriptEnabled") 
public class ShowWebChartActivity extends ActionBarActivity {
 
 WebView webView;
 int num1, num2, num3, num4, num5;
 
 Spinner spCharts;
 List listCharts;
 List listHtml;
 
 Button btnCapture;

 @Override
 protected void onCreate(Bundle savedInstanceState) {
  super.onCreate(savedInstanceState);
        setContentView(R.layout.layout_webchart);
        
        Intent intent = getIntent();
        num1 = intent.getIntExtra("NUM1", 0);
        num2 = intent.getIntExtra("NUM2", 0);
        num3 = intent.getIntExtra("NUM3", 0);
        num4 = intent.getIntExtra("NUM4", 0);
        num5 = intent.getIntExtra("NUM5", 0);
        
        spCharts = (Spinner) findViewById(R.id.spcharts);
        
        listCharts = new ArrayList();
        listCharts.add("Pie Chart");
        listCharts.add("Pie Chart 3D");
        listCharts.add("Scatter Chart");
        listCharts.add("Column Chart");
        listCharts.add("Bar Chart");
        listCharts.add("Histogram");
        listCharts.add("Line Chart");
        listCharts.add("Area Chart");
        
        listHtml = new ArrayList();
        listHtml.add("file:///android_asset/pie_chart.html");
        listHtml.add("file:///android_asset/pie_chart_3d.html");
        listHtml.add("file:///android_asset/scatter_chart.html");
        listHtml.add("file:///android_asset/column_chart.html");
        listHtml.add("file:///android_asset/bar_chart.html");
        listHtml.add("file:///android_asset/histogram.html");
        listHtml.add("file:///android_asset/line_chart.html");
        listHtml.add("file:///android_asset/area_chart.html");
        
     ArrayAdapter dataAdapter = new ArrayAdapter(this,
      android.R.layout.simple_spinner_item, listCharts);
     dataAdapter.setDropDownViewResource(android.R.layout.simple_spinner_dropdown_item);
     spCharts.setAdapter(dataAdapter);
     spCharts.setOnItemSelectedListener(new OnItemSelectedListener(){

   @Override
   public void onItemSelected(AdapterView parent, View view,
     int position, long id) {
    String chartHtml = listHtml.get(parent.getSelectedItemPosition());
    webView.loadUrl(chartHtml);
   }

   @Override
   public void onNothingSelected(AdapterView parent) {
    // TODO Auto-generated method stub
    
   }});
        
        webView = (WebView)findViewById(R.id.web);
        webView.addJavascriptInterface(new WebAppInterface(), "Android");

        webView.getSettings().setJavaScriptEnabled(true); 

        btnCapture = (Button)findViewById(R.id.capture);
        btnCapture.setOnClickListener(new OnClickListener(){

   @Override
   public void onClick(View v) {
    //call Javascript in WebView/HTML
    webView.loadUrl("javascript:capture()");
   }});
 }
 
 private void showCaptured(String imageuri){

  Bitmap bmp = decodeBase64PNG(imageuri);
  
  Dialog dialog = new Dialog(this);
     ImageView imageView = new ImageView(this);
     imageView.setImageBitmap(bmp);
     dialog.addContentView(
       imageView, 
       new LayoutParams(
        LayoutParams.MATCH_PARENT, 
        LayoutParams.MATCH_PARENT));
     dialog.show();
  
 }
 
 private Bitmap decodeBase64PNG(String src){

  String imageDataBytes = src.substring(src.indexOf(",") + 1);
  
  InputStream stream = 
   new ByteArrayInputStream(
    Base64.decode(imageDataBytes.getBytes(), 
    Base64.DEFAULT));
  
     Bitmap bitmap = BitmapFactory.decodeStream(stream);
     return bitmap;
 }

 public class WebAppInterface {

     @JavascriptInterface
  public int getNum1() {
   return num1;
  }
  
  @JavascriptInterface
  public int getNum2() {
   return num2;
  }
  
  @JavascriptInterface
  public int getNum3() {
   return num3;
  }
  
  @JavascriptInterface
  public int getNum4() {
   return num4;
  }
  
  @JavascriptInterface
  public int getNum5() {
   return num5;
  }
  
  @JavascriptInterface
  public void captureCallback(String imageURI){
   Toast.makeText(ShowWebChartActivity.this, 
    imageURI, Toast.LENGTH_LONG).show();
   showCaptured(imageURI);
  }
 }

}

All other HTMLs:

• add a method Javascript function capture() to be called from Android, and call chart.getImageURI() to get image, and pass back to Android by calling captureCallback().
• Make chart to global by removing "var" in front of it.

pie_chart.html

pie_chart_3d.html

scatter_chart.html

column_chart.html

bar_chart.html

histogram.html

line_chart.html

area_chart.html

Download the files.