<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"    xmlns:tools="http://schemas.android.com/tools"    android:layout_width="match_parent"    android:layout_height="match_parent"    android:orientation="vertical"    tools:context="com.example.paint.MainActivity" >    <Button        android:onClick="save"        android:id="@+id/btn"        android:layout_width="fill_parent"        android:layout_height="wrap_content"        android:text="保存" />    <Button        android:onClick="selectImage"        android:id="@+id/select"        android:layout_width="fill_parent"        android:layout_height="wrap_content"        android:text="选择一个图片" />    <ImageView        android:layout_above="@id/select"        android:id="@+id/iv"        android:layout_width="fill_parent"        android:layout_height="fill_parent"        /></LinearLayout>

package com.example.paint;import java.io.File;import java.io.FileOutputStream;import android.content.Intent;import android.graphics.Bitmap;import android.graphics.Bitmap.CompressFormat;import android.graphics.Bitmap.Config;import android.graphics.Canvas;import android.graphics.Color;import android.graphics.Paint;import android.net.Uri;import android.os.Bundle;import android.os.Environment;import android.support.v7.app.ActionBarActivity;import android.view.MotionEvent;import android.view.View;import android.view.View.OnTouchListener;import android.widget.ImageView;import android.widget.Toast;public class MainActivity extends ActionBarActivity {    private ImageView iv;        private Bitmap baseBitmap;        private Canvas canvas; //画布        private Paint paint; //画笔            @Override    protected void onCreate(Bundle savedInstanceState) {        super.onCreate(savedInstanceState);        setContentView(R.layout.activity_main);                paint = new Paint();        //画笔宽度        paint.setStrokeWidth(5);        //画笔颜色        paint.setColor(Color.GREEN);                //创建一个可以修改的bitmap        baseBitmap = Bitmap.createBitmap(320, 350, Config.ARGB_8888);        //创建一个画布        canvas = new Canvas(baseBitmap);        //设置背景色        canvas.drawColor(Color.WHITE);                iv = (ImageView)findViewById(R.id.iv);                //知道用户手指在平美国上移动的轨迹        iv.setOnTouchListener(new OnTouchListener() {            //获取手指开始位置的坐标            int startX;            int startY;            @Override            public boolean onTouch(View v, MotionEvent event) {                            switch(event.getAction())                {                    case MotionEvent.ACTION_DOWN: //手指第一次接触屏幕                                            startX = (int)event.getX();                        startY = (int)event.getY();                        break;                    case MotionEvent.ACTION_MOVE: //手指在屏幕上移动                                                int newX = (int)event.getX();                        int newY = (int)event.getY();                        //画线                        canvas.drawLine(startX, startY, newY, newY, paint);                                                //重新更新画笔开始位置                        startX =  (int)event.getX();                        startY = (int)event.getY();                                                iv.setImageBitmap(baseBitmap);                        break;                    case MotionEvent.ACTION_UP: //手指离开屏幕的动作                                                break;                                }                                //return true 表示画笔一直触动                return true;            }                    });    }                public void selectImage(View view)    {        Intent intent = new Intent();        intent.setAction(Intent.ACTION_PICK);        intent.setType("image/*");        startActivityForResult(intent, 0);            }        @Override    protected void onActivityResult(int arg0, int arg1, Intent data) {        if(data!=null)        {                        Uri uri = data.getData();            Bitmap bitmap = data.getParcelableExtra("data");            baseBitmap = bitmap;            iv.setImageURI(uri);                    }        super.onActivityResult(arg0, arg1, data);    }            public void save(View view)    {           try {                        File file = new File(Environment.getExternalStorageDirectory(),System.currentTimeMillis()+".jpg");            FileOutputStream fos = new FileOutputStream(file);            //保存图片            baseBitmap.compress(CompressFormat.JPEG, 100, fos);                        Toast.makeText(this, "保存图片成功", 0).show();                        //模拟一个消息通知系统sd卡被重新挂载            Intent intent = new Intent();            intent.setAction(Intent.ACTION_MEDIA_MOUNTED);            intent.setData(Uri.fromFile(Environment.getExternalStorageDirectory()));            sendBroadcast(intent);                    } catch (Exception e) {            Toast.makeText(this, "保存图片失败", 0).show();            e.printStackTrace();        }            }  }