Android 实现简单的画画版一

原理：
1）首先创建一个创建一张空白图片
2）把空白图片设置到imageview控件
3）给imageview设置监听，并返回值true;

代码如下:

/**
 * @描述         画板
 * @项目名称      App_Basic
 * @包名         com.example.basic.image
 * @类名         CanvaImage
 * @author      chenlin
 * @version     1.0
 */

public class CanvaImageActivty extends BaseActivity implements OnTouchListener, OnClickListener {
    private Button mBtnView;
    private ImageView mImageView;
    private Bitmap mBlankBitmap;
    private Canvas mCanvas;
    private Paint mPaint;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_canvas);
        mBtnView = (Button) findViewById(R.id.btn_view_image);
        mImageView = (ImageView) findViewById(R.id.iv_canvas);

        mImageView.setOnTouchListener(this);
        mBtnView.setOnClickListener(this);

        createBitmap();
    }

    private void createBitmap() {
        WindowManager manager = (WindowManager) getSystemService(WINDOW_SERVICE);
        DisplayMetrics outMetrics = new DisplayMetrics();
        manager.getDefaultDisplay().getMetrics(outMetrics);
        mBtnView.measure(0, 0);

        int height = outMetrics.heightPixels - mBtnView.getMeasuredHeight();
        // 创建一张空白图片
        mBlankBitmap = Bitmap.createBitmap(outMetrics.widthPixels, height, Config.ARGB_8888);
        // 创建一张画布
        mCanvas = new Canvas(mBlankBitmap);
        //画布背景为白色
        mCanvas.drawColor(Color.WHITE);

        //初始化画笔
        mPaint = new Paint();
        mPaint.setColor(Color.RED);
        mPaint.setStrokeWidth(3);

        //绘制白色背景
        mCanvas.drawBitmap(mBlankBitmap, new Matrix(), mPaint);
        mImageView.setImageBitmap(mBlankBitmap);
    }

    private int downX;
    private int downY;
    @Override
    public boolean onTouch(View v, MotionEvent event) {
        switch (event.getAction()) {
        case MotionEvent.ACTION_DOWN:
            // 获取手按下时的坐标
            downX = (int) event.getX();
            downY = (int) event.getY();
            break;
        case MotionEvent.ACTION_MOVE:
            // 获取手移动后的坐标
            int moveX = (int) event.getX();
            int moveY = (int) event.getY();

            // 在开始和结束坐标间画一条线
            mCanvas.drawLine(downX, downY, moveX, moveY, mPaint);
            // 实时更新开始坐标
            downX = (int) event.getX();
            downY = (int) event.getY();
            mImageView.setImageBitmap(mBlankBitmap);
            break;
        case MotionEvent.ACTION_UP:
        case MotionEvent.ACTION_CANCEL:
            //mImageView.setImageBitmap(mBlankBitmap);
            //保存图片到sdcard
            saveBitmap(mBlankBitmap);
            break;

        }
        return true;
    }

    private void saveBitmap(Bitmap bitmap) {
        try {
            String path = Environment.getExternalStorageDirectory().getAbsolutePath() + "/image/";
            File dir = new File(path);
            if (!dir.exists()) {
                dir.mkdirs();
            }
            String filename = System.currentTimeMillis() + ".jpg";
            FileOutputStream fos = new FileOutputStream(new File(path, filename));
            //把保存图片
            bitmap.compress(CompressFormat.JPEG, 100, fos);
            fos.close();

            notifyHasMount();


        } catch (FileNotFoundException e) {
            e.printStackTrace();
            show("保存失败" + e.getMessage());
        } catch (IOException e) {
            e.printStackTrace();
            show("保存失败" + e.getMessage());
        }
    }

    /**
     * 模拟一个广播，通知系统sdcard被挂载
     * */
    private void notifyHasMount() {
        Intent intent = new Intent();
        intent.setAction(Intent.ACTION_MEDIA_MOUNTED);
        intent.setData(Uri.fromFile(Environment.getExternalStorageDirectory()));
        sendBroadcast(intent);
    }
    /**
     * 查看图片
     */
    @Override
    public void onClick(View v) {
        if (v == mBtnView) {
            Intent intent = new Intent();
            intent.setAction(Intent.ACTION_PICK);
            intent.setType("image/*");
            startActivity(intent);
        }

    }
}

布局文件

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:orientation="vertical" >

    <ImageView
        android:id="@+id/iv_canvas"
        android:layout_width="match_parent"
        android:layout_height="0dp"
        android:layout_weight="1"

        />

    <Button
        android:id="@+id/btn_view_image"
        android:gravity="center"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:text="查看图片" />

</LinearLayout>