缩放图片 : matrix.setScale(0.5f,0.5f);

public class MainActivity extends Activity implements OnClickListener {

      private  Button  bt;

      private  ImageView  iv;

      private  ImageView  iv_after;

      

      @Override

      protected void onCreate(Bundle savedInstanceState) {

             super.onCreate(savedInstanceState);

            setContentView(R.layout. activity_main);

            

             iv=(ImageView) findViewById(R.id. iv);

             bt=(Button) findViewById(R.id. bt);

             iv_after=(ImageView) findViewById(R.id. iv_after);

            

            

             bt.setOnClickListener( this);

            

      }

      

      

      /**

       * 获取图片的方法

       * @param v

       */

      @Override

      public void onClick(View v) {

            

             //创建隐式意图

        Intent intent= new Intent();

        intent.setAction( "android.intent.action.PICK");

        intent.addCategory(intent. CATEGORY_DEFAULT);

        intent.setType( "image/*");

       

        startActivityForResult(intent, 0);

    }

      

      

      

      /**

     * 获取Activity返回的数据

     */

    @Override

    protected void onActivityResult( int requestCode, int resultCode, Intent data) {

           super.onActivityResult(requestCode, resultCode, data);

         

          Uri uri = data.getData();   //接收到返回照片的 uri

          iv.setImageURI(uri);  

         

          try {

               

             //得到原图的bitmap   只读(要从这个bitmap读取像素点到其他的空白bitmap上)

                  Bitmap  bitmap=BitmapFactory.decodeStream(getContentResolver().openInputStream(uri));

                  

                   //创建一个空白可修改的bitmap   b1

                  Bitmap  alertBitmap=Bitmap.createBitmap(bitmap.getWidth()/2, bitmap.getHeight()/2, bitmap.getConfig());

                  

                   //将空白可修改的bitmap作为画布    b2

                  Canvas  canvas= new Canvas(alertBitmap);

                  

                   //创建画笔

                  Paint  paint= new  Paint();

                  paint.setColor(Color. GREEN);

                  

                   //在画布上画原图片的像素点

                Matrix matrix = new  Matrix();

                matrix.setScale(0.5f,0.5f);   //设置x,y方向的缩放比   

                canvas.drawBitmap(bitmap, matrix, paint);   //1.原图  2.矩阵   3.画笔

                  

                //将画好的b2挂在iv上

                iv_after.setImageBitmap(alertBitmap);

                  

            } catch (Exception e) {

                  

                  e.printStackTrace();

            }

          

          

    }

}