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mainActivity如下:

package c.c;import android.app.Activity;import android.content.Intent;import android.graphics.Bitmap;import android.graphics.BitmapFactory;import android.graphics.Canvas;import android.graphics.Paint;import android.graphics.PorterDuffXfermode;import android.net.Uri;import android.os.Bundle;import android.provider.MediaStore;import android.view.View;import android.view.View.OnClickListener;import android.widget.Button;import android.widget.ImageView;/** * 需求描述: * 从相册中选取两张图片合成一张图片 *  * 小结: * 1 依据图片的Uri加载图片 * mBitmap1=BitmapFactory.decodeStream * (getContentResolver().openInputStream(photoFileUri)); * 为什么使用getContentResolver呢？因为在相册本身是一个内容提供者 * 2 注意构造方法: * Canvas canvas=new Canvas(bitmap); * 为什么要传入一个bitmap呢？ * 我们画东西肯定是在画布上画. * 但是在这里传入一个bitmap * 即该bitmap是一个载体,相当于把bitmap作为了画布. * 当然本质上是:把东西画在了canvas里的bitmap上 * 也可以这么想: * 我们最后不是要用mImageView.setImageBitmap(参数是一个Bitmap)来显示 * 一张图片么？所以在构造Canvas的时候传入了一个Bitmap.然后把两张图片 * 画到了该Bitmap上.最后该Bitmap就是两张照片的合成图. * 所以当然要把两张图片画到一个Bitmap上 */public class MainActivity extends Activity {	private static int REQUESTCODE=0;	private final static int PICK_FIRST_PHOTO=1;	private final static int PICK_SECOND_PHOTO=2;	private boolean isPickedFirstPhoto=false;	private boolean isPickedSecondPhoto=false;    private Button mButton1;    private Button mButton2;    private Bitmap mBitmap1;    private Bitmap mBitmap2;    private ImageView mImageView;        @Override    public void onCreate(Bundle savedInstanceState) {        super.onCreate(savedInstanceState);        setContentView(R.layout.main);        init();    }    private void init(){    	mButton1=(Button) findViewById(R.id.button1);    	mButton1.setOnClickListener(new ButtonOnClickListenerImpl());    	mButton2=(Button) findViewById(R.id.button2);    	mButton2.setOnClickListener(new ButtonOnClickListenerImpl());    	mImageView=(ImageView) findViewById(R.id.imageView);    }    private class ButtonOnClickListenerImpl implements OnClickListener{		public void onClick(View v) {			if (v.getId()==R.id.button1) {				REQUESTCODE=PICK_FIRST_PHOTO;			} else {				REQUESTCODE=PICK_SECOND_PHOTO;			}			Intent intent=new Intent(Intent.ACTION_PICK, MediaStore.Images.Media.EXTERNAL_CONTENT_URI);			startActivityForResult(intent, REQUESTCODE);		}    	    }    @Override    protected void onActivityResult(int requestCode, int resultCode, Intent data) {    	super.onActivityResult(requestCode, resultCode, data);    	if (resultCode==RESULT_OK) {    		Uri photoFileUri=data.getData();			if (requestCode==PICK_FIRST_PHOTO) {				try {					mBitmap1=BitmapFactory.decodeStream					(getContentResolver().openInputStream(photoFileUri));					isPickedFirstPhoto=true;				} catch (Exception e) {					e.printStackTrace();				}			}			if (requestCode==PICK_SECOND_PHOTO) {				try {					mBitmap2=BitmapFactory.decodeStream					(getContentResolver().openInputStream(photoFileUri));					isPickedSecondPhoto=true;				} catch (Exception e) {					e.printStackTrace();				}			}			if (isPickedFirstPhoto&&isPickedSecondPhoto) {				Bitmap bitmap=				Bitmap.createBitmap(mBitmap1.getWidth(), mBitmap1.getHeight(), mBitmap1.getConfig());				Canvas canvas=new Canvas(bitmap);				Paint paint=new Paint();				canvas.drawBitmap(mBitmap1, 0, 0, paint);				paint.setXfermode(new PorterDuffXfermode(android.graphics.PorterDuff.Mode.MULTIPLY));				canvas.drawBitmap(mBitmap2, 0, 0,paint);				mImageView.setImageBitmap(bitmap);							}		}    }}

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