安卓 加载图片并在上面画图

package com.example.fingerdraw;

import java.io.FileNotFoundException;
import java.io.OutputStream;

import android.app.Activity;
import android.content.ContentValues;
import android.content.Intent;
import android.graphics.Bitmap;
import android.graphics.Bitmap.CompressFormat;
import android.graphics.BitmapFactory;
import android.graphics.Canvas;
import android.graphics.Color;
import android.graphics.Matrix;
import android.graphics.Paint;
import android.net.Uri;
import android.os.Bundle;
import android.provider.MediaStore.Images.Media;
import android.view.Display;
import android.view.MotionEvent;
import android.view.View;
import android.view.View.OnClickListener;
import android.view.View.OnTouchListener;
import android.widget.Button;
import android.widget.ImageView;
import android.widget.Toast;

public class MainActivity extends Activity implements OnTouchListener,
OnClickListener {

private ImageView image;
private Paint paint;
private Canvas canvas;
private Bitmap bitmap;
private Bitmap alterBitmap;
private Button choose;
private Button save;
private final static int RESULT = 0;

@Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
image = (ImageView) findViewById(R.id.image);
choose = (Button) findViewById(R.id.chooseButton);
save=(Button)findViewById(R.id.saveButton);
/*
* bitmap = Bitmap.createBitmap(getWindowManager().getDefaultDisplay()
* .getWidth(), getWindowManager().getDefaultDisplay().getHeight(),
* Bitmap.Config.ARGB_8888); canvas = new Canvas(bitmap);// 画板 paint =
* new Paint();// 画刷 paint.setColor(Color.BLUE);
* image.setImageBitmap(bitmap);
*/

image.setOnTouchListener(this);
choose.setOnClickListener(this);
save.setOnClickListener(this);
}

private float downx = 0;
private float downy = 0;
private float upx = 0;
private float upy = 0;

public boolean onTouch(View v, MotionEvent event) {
int action = event.getAction();
switch (action) {
case MotionEvent.ACTION_DOWN:
downx = event.getX();
downy = event.getY();
break;
case MotionEvent.ACTION_MOVE:
// 路径画板
upx = event.getX();
upy = event.getY();
canvas.drawLine(downx, downy, upx, upy, paint);
image.invalidate();
downx = upx;
downy = upy;
break;
case MotionEvent.ACTION_UP:
// 直线画板

upx = event.getX();
upy = event.getY();
canvas.drawLine(downx, downy, upx, upy, paint);
image.invalidate();// 刷新
break;

default:
break;
}

return true;
}

public void onClick(View arg0) {
if(arg0==choose){
Intent intent = new Intent(Intent.ACTION_PICK,
android.provider.MediaStore.Images.Media.EXTERNAL_CONTENT_URI);
startActivityForResult(intent, RESULT);
}else if(arg0==save){
//保存画好的图片
if(alterBitmap!=null){
try {
Uri imageUri=getContentResolver().insert(Media.EXTERNAL_CONTENT_URI, new ContentValues());
OutputStream outputStream=getContentResolver().openOutputStream(imageUri);
alterBitmap.compress(CompressFormat.PNG, 90, outputStream);
Toast.makeText(getApplicationContext(), "save!", Toast.LENGTH_SHORT).show();
} catch (FileNotFoundException e) {
e.printStackTrace();
}
}
}
}

@Override
protected void onActivityResult(int requestCode, int resultCode, Intent data) {
// TODO Auto-generated method stub
super.onActivityResult(requestCode, resultCode, data);
if (resultCode == RESULT_OK) {
Uri imageFileUri = data.getData();
Display display = getWindowManager().getDefaultDisplay();
float dw = display.getWidth();
float dh = display.getHeight();

try {
BitmapFactory.Options options = new BitmapFactory.Options();
options.inJustDecodeBounds = true;
bitmap = BitmapFactory.decodeStream(getContentResolver()
.openInputStream(imageFileUri), null, options);
int heightRatio = (int) Math.ceil(options.outHeight / dh);
int widthRatio = (int) Math.ceil(options.outWidth / dw);
if (heightRatio > 1 && widthRatio > 1) {
if (heightRatio > widthRatio) {
options.inSampleSize = heightRatio;
} else {
options.inSampleSize = widthRatio;
}
}
options.inJustDecodeBounds = false;
bitmap = BitmapFactory.decodeStream(getContentResolver()
.openInputStream(imageFileUri), null, options);
alterBitmap = Bitmap.createBitmap(bitmap.getWidth(),
bitmap.getHeight(), bitmap.getConfig());
canvas = new Canvas(alterBitmap);
paint = new Paint();
paint.setColor(Color.GREEN);
paint.setStrokeWidth(10);
Matrix matrix = new Matrix();
canvas.drawBitmap(bitmap, matrix, paint);
image.setImageBitmap(alterBitmap);
image.setOnTouchListener(this);
} catch (FileNotFoundException e) {

e.printStackTrace();
}

}
}

}

效果：