Android -- 图片画画板（canvas、paint、bitmap）

布局文件：

<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"
    >
    <ImageView 
        android:id="@+id/iv"
        android:layout_weight="1"
        android:layout_width="match_parent"
        android:layout_height="match_parent"
        />
    <Button
        android:id="@+id/btn"
        android:layout_weight="6"
        android:onClick="save"
        android:layout_width="match_parent"
        android:layout_height="match_parent"
        android:text="保存图片"
        />
</LinearLayout>

MainActivity：

public class MainActivity extends Activity {
                     
    private Button button;
    private ImageView p_w_picpathView;
    private Bitmap baseBitmap;
    private Canvas canvas;
    private Paint paint;
                         
    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        p_w_picpathView=(ImageView) findViewById(R.id.iv);
                         
        paint=new Paint();
        paint.setColor(Color.BLUE);
                         
        //创建一个可修改的Bitmap
        baseBitmap=Bitmap.createBitmap(480, 320, Bitmap.Config.ARGB_8888);
        canvas=new Canvas(baseBitmap);
        canvas.drawColor(Color.WHITE);
                         
        p_w_picpathView.setOnTouchListener(new OnTouchListener() {
            //定义手指坐标
            int startx;
            int starty;
                                     
            @Override
            public boolean onTouch(View v, MotionEvent event) {
                switch (event.getAction()) {
                case MotionEvent.ACTION_DOWN:
                                     
                    startx=(int) event.getX();
                    starty=(int) event.getY();             
                    break;
                case MotionEvent.ACTION_MOVE:
                    int newx=(int) event.getX();
                    int newy=(int) event.getY();
                    canvas.drawLine(startx, starty, newx, newy, paint);
                    //跟新画笔的开始位置
                    startx=(int) event.getX();
                    starty=(int) event.getY(); 
                    p_w_picpathView.setImageBitmap(baseBitmap);
                    break;
                case MotionEvent.ACTION_UP:
                                     
                    break;
                }
                return true;
            }
        });    
    }
    public void save(View v) {
                         
        try {
            File file=new File(Environment.getExternalStorageDirectory(), System.currentTimeMillis()+".jpg");
            FileOutputStream fos=new FileOutputStream(file);
            baseBitmap.compress(CompressFormat.JPEG, 100, fos);//第一个参数为图片格式
            fos.close();
            Toast.makeText(this, "保存图片成功", 2000).show();
            //模拟消息：SD卡被重新挂载了
            Intent intent=new Intent();
            intent.setAction(intent.ACTION_MEDIA_MOUNTED);
            intent.setData(Uri.fromFile(Environment.getExternalStorageDirectory()));
            sendBroadcast(intent);
        } catch (FileNotFoundException e) {
            Toast.makeText(this, "保存图片失败", 2000).show();
            e.printStackTrace();
        } catch (IOException e) {
            e.printStackTrace();
        }              
    }
}

因为要存入SD中，所以还要加一个权限：

<uses-permission android:name="android.permission.WRITE_EXTERNAL_STORAGE"/>

运行结果：