Working With Images In Android

Using BitmapDrawable To Create Bitmaps

BitmapDrawables are simply Drawable objects that wrap a bitmap and can be created from file path, input stream, XML inflation from a layout, and bitmaps.

Building Bitmap Objects

File

Use the adb tool with push option to copy test2.png onto the sdcard.

bash-3.1$ /usr/local/android-sdk-linux/tools/adb push test2.png /sdcard/

This is the easiest way to load bitmaps from the sdcard. Simply pass the path to the image to BitmapFactory.decodeFile() and let the Android SDK do the rest.

package higherpass.TestImages;

import android.app.Activity;
import android.graphics.Bitmap;
import android.graphics.BitmapFactory;
import android.os.Bundle;
import android.widget.ImageView;

public class TestImages extends Activity {
    /** Called when the activity is first created. */
    @Override
    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.main);
        ImageView image = (ImageView) findViewById(R.id.test_image);
        Bitmap bMap = BitmapFactory.decodeFile("/sdcard/test2.png");
        image.setImageBitmap(bMap);
    }
}

All this code does is load the image test2.png that we previously copied to the sdcard. The BitmapFactory creates a bitmap object with this image and we use the ImageView.setImageBitmap() method to update the ImageView component.

Input stream

Use BitmapFactory.decodeStream() to convert a BufferedInputStream into a bitmap object.

package higherpass.TestImages;

import java.io.BufferedInputStream;
import java.io.FileInputStream;

import android.app.Activity;
import android.graphics.Bitmap;
import android.graphics.BitmapFactory;
import android.os.Bundle;
import android.util.Log;
import android.widget.ImageView;

public class TestImages extends Activity {
    /** Called when the activity is first created. */
    @Override
    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.main);
        ImageView image = (ImageView) findViewById(R.id.test_image);
        FileInputStream in;
        BufferedInputStream buf;
        try {
       	    in = new FileInputStream("/sdcard/test2.png");
            buf = new BufferedInputStream(in);
            Bitmap bMap = BitmapFactory.decodeStream(buf);
            image.setImageBitmap(bMap);
            if (in != null) {
         	in.close();
            }
            if (buf != null) {
         	buf.close();
            }
        } catch (Exception e) {
            Log.e("Error reading file", e.toString());
        }
    }
}

This code uses the basic Java FileInputStream and BufferedInputStream to create the input stream for BitmapFactory.decodeStream(). The file access code should be surrounded by a try/catch block to catch any exceptions thrown by FileInputStream or BufferedInputStream. Also when you're finished with the stream handles they should be closed.

XML inflation

Bitmaps can be extracted from layouts and views with inflation. Use BitmapFactory.decodeResource(res, id) to get a bitmap from an Android resource.

    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.main);
        ImageView image = (ImageView) findViewById(R.id.test_image);
        Bitmap bMap = BitmapFactory.decodeResource(getResources(), R.drawable.icon);
        image.setImageBitmap(bMap);
    }

First create an ImageView instance containing the ImageView from the layout. Then create a bitmap from the application icon (R.drawable.icon) with BitmapFactory.decodeResource(). Finally set the new bitmap to be the image displayed in the ImageView component of the layout.

Bitmaps

The BitmapFactory.decodeByteArray() method of creating bitmaps creates a bitmap from an array of bytes. This is useful when a bitmap has been loaded for another purpose or has been created by the application or other external source.

package higherpass.TestImages; 

import java.io.BufferedInputStream;
import java.io.FileInputStream;

import android.app.Activity;
import android.graphics.Bitmap;
import android.graphics.BitmapFactory;
import android.os.Bundle;
import android.util.Log;
import android.widget.ImageView;

public class TestImages extends Activity {
    /** Called when the activity is first created. */
    @Override
    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.main);
        ImageView image = (ImageView) findViewById(R.id.test_image);
        FileInputStream in;
        BufferedInputStream buf;
        try {
       	    in = new FileInputStream("/sdcard/test2.png");
            buf = new BufferedInputStream(in);
            byte[] bMapArray= new byte[buf.available()];
            buf.read(bMapArray);
            Bitmap bMap = BitmapFactory.decodeByteArray(bMapArray, 0, bMapArray.length);
            image.setImageBitmap(bMap);
            if (in != null) {
         	in.close();
            }
            if (buf != null) {
         	buf.close();
            }
        } catch (Exception e) {
            Log.e("Error reading file", e.toString());
        }
    }
}

As with the decodeStream() example we open the file in an input stream. This time though we go the extra mile and manually read the file into a byte array. This isn't the best way to do this if you haven't noticed, but it's a simple way to show the functionality. Use the BitmapFactory.decodeByteArray() method to create the bitmap. This function expects 3 parameters, the byte array, the array offset to start from, and the array offset to stop at.