利用Matrix類對位圖(bitmap)進行放大和縮小

本練習利用Matrix類的postScale()方法, 通過Bitmap.createBitmap()方法從一個源位圖創建另一個縮放位圖, 從而做到放大和縮小的效果.

(本應用程序如果進行太大的縮放會發生錯誤, 但這不是本練習的重點, 所以筆者沒有特別處理.)



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"
    />
<LinearLayout 
    android:orientation="horizontal"
    android:layout_width="fill_parent" 
    android:layout_height="wrap_content" 
    android:gravity="center_horizontal"
    >
<Button
    android:id="@+id/enlarge"
    android:layout_width="wrap_content" 
    android:layout_height="wrap_content" 
    android:text=" Enlarge + "
    />
<Button
    android:id="@+id/reset"
    android:layout_width="wrap_content" 
    android:layout_height="wrap_content" 
    android:text=" Original Size "
    />
<Button
    android:id="@+id/Reduce"
    android:layout_width="wrap_content" 
    android:layout_height="wrap_content" 
    android:text=" Reduce - "
    />
</LinearLayout>
<ImageView  
    android:id="@+id/imageview"
    android:layout_gravity="center"
    android:layout_width="fill_parent" 
    android:layout_height="fill_parent" 
    android:scaleType="center"
    />
</LinearLayout>

AndroidImage.java

package com.AndroidImage;

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.Button;
import android.widget.ImageView;

public class AndroidImage extends Activity {
 
 private ImageView myImageView;
 private float scale;
 private 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);

        Button buttonEnlarge = (Button)findViewById(R.id.enlarge);
        Button buttonReset = (Button)findViewById(R.id.reset);
        Button buttonReduce = (Button)findViewById(R.id.Reduce);

        bitmap = BitmapFactory.decodeResource(getResources(), R.drawable.icon);
        bmpWidth = bitmap.getWidth();
        bmpHeight = bitmap.getHeight();
        scale= 1;
        
        loadImage();
        
        buttonEnlarge.setOnClickListener(new Button.OnClickListener(){

   @Override
   public void onClick(View v) {
    // TODO Auto-generated method stub
    scale *= 2;
    loadImage();
    
   }});
        
        buttonReset.setOnClickListener(new Button.OnClickListener(){

   @Override
   public void onClick(View v) {
    // TODO Auto-generated method stub
    scale = 1;
    loadImage();
    
   }});
        
        buttonReduce.setOnClickListener(new Button.OnClickListener(){

   @Override
   public void onClick(View v) {
    // TODO Auto-generated method stub
    scale *= 0.5;
    loadImage();
    
   }});
        
    }
    
    private void loadImage(){
     
     Matrix matrix = new Matrix();
     matrix.postScale(scale, scale);
     
     Bitmap resizedBitmap = Bitmap.createBitmap(bitmap, 0, 0, bmpWidth, bmpHeight, matrix, true);
     myImageView.setImageBitmap(resizedBitmap);

    }
}