Scale bitmap image, using Matrix

Modify the last exercise "Load bitmap file from SD Card", to implement function to post-scale the bitmap image using Matrix.



In order to create a new bitmap with selected scale: A new Matrix object have to be created, with postScale. Then create a new bitmap from the image in SD Card, using the matrix.

Modify main.xml

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
 android:orientation="vertical"
 android:layout_width="fill_parent"
 android:layout_height="fill_parent"
 >
<TextView
 android:layout_width="fill_parent"
 android:layout_height="wrap_content"
 android:text="@string/hello"
 />
<Spinner
 android:id="@+id/scale"
 android:layout_width="fill_parent"
 android:layout_height="wrap_content"
 />
<ImageView
 android:id="@+id/imageview"
 android:layout_gravity="center"
 android:layout_width="fill_parent"
 android:layout_height="fill_parent"
 android:scaleType="center"
 />
</LinearLayout>

AndroidBitmap.java

package com.exercise.AndroidBitmap;

import android.app.Activity;
import android.graphics.Bitmap;
import android.graphics.BitmapFactory;
import android.graphics.Matrix;
import android.os.Bundle;
import android.view.View;
import android.widget.AdapterView;
import android.widget.ArrayAdapter;
import android.widget.ImageView;
import android.widget.Spinner;

public class AndroidBitmap extends Activity {

private final String imageInSD = "/sdcard/er.PNG";

ImageView myImageView;
Spinner spinnerScale;

private static final String[] strScale
 = {"0.2x", "0.5x", "1.0x", "2.0x", "5.0x"};
private static final Float[] floatScale
 = {0.2F, 0.5F, 1F, 2F, 5F};
private final int defaultSpinnerScaleSelection = 2;

private ArrayAdapter<String> adapterScale;

private float curScale = 1F;

Bitmap bitmap;
int bmpWidth, bmpHeight;

 /** Called when the activity is first created. */
 @Override
 public void onCreate(Bundle savedInstanceState) {
     super.onCreate(savedInstanceState);
     setContentView(R.layout.main);
  
     myImageView = (ImageView)findViewById(R.id.imageview);
  
     spinnerScale = (Spinner)findViewById(R.id.scale);
     adapterScale = new ArrayAdapter<String>(this,
             android.R.layout.simple_spinner_item, strScale);
     adapterScale.setDropDownViewResource(android.R.layout.simple_spinner_dropdown_item);
     spinnerScale.setAdapter(adapterScale);
     spinnerScale.setSelection(defaultSpinnerScaleSelection);
     curScale = floatScale[defaultSpinnerScaleSelection];
  
     bitmap = BitmapFactory.decodeFile(imageInSD);
     bmpWidth = bitmap.getWidth();
     bmpHeight = bitmap.getHeight();
  
     drawMatrix();
  
     spinnerScale.setOnItemSelectedListener(spinnerScaleOnItemSelectedListener);

 }

 private void drawMatrix(){
 
  Matrix matrix = new Matrix();
     matrix.postScale(curScale, curScale);
   
     Bitmap resizedBitmap = Bitmap.createBitmap(bitmap, 0, 0, bmpWidth, bmpHeight, matrix, true);
     myImageView.setImageBitmap(resizedBitmap);
 
 }

 private Spinner.OnItemSelectedListener spinnerScaleOnItemSelectedListener
  = new Spinner.OnItemSelectedListener(){

  @Override
  public void onItemSelected(AdapterView<?> arg0, View arg1,
    int arg2, long arg3) {
   // TODO Auto-generated method stub
   curScale = floatScale[arg2];
   drawMatrix();
  }

  @Override
  public void onNothingSelected(AdapterView<?> arg0) {
   // TODO Auto-generated method stub
   spinnerScale.setSelection(defaultSpinnerScaleSelection);
   curScale = floatScale[defaultSpinnerScaleSelection];
  }};
}

Download the files.

next: Rotate bitmap image, using Matrix