Android画板的实现

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:tools="http://schemas.android.com/tools"
    android:id="@+id/activity_main2"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:orientation="vertical"
    tools:context="com.example.dell.myapplication.Main2Activity">

    <LinearLayout
        android:orientation="horizontal"
        android:layout_width="match_parent"
        android:layout_height="wrap_content">

        <Button
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:onClick="bold"
            android:text="变粗" />

        <Button
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:onClick="changeColor"
            android:text="改变颜色" />

        <Button
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:onClick="save"
            android:text="保存图片" />


    </LinearLayout>

    <LinearLayout
        android:layout_width="wrap_content"
        android:layout_height="wrap_content">

        <ImageView
            android:id="@+id/iv_image"
            android:layout_width="wrap_content"
            android:layout_height="wrap_content" />
    </LinearLayout>

</LinearLayout>

public class Main2Activity extends AppCompatActivity {
    private ImageView imageView;
    private Bitmap copyBitmap;
    private Paint paint;
    private Canvas canvas;
    private float startX;
    private float startY;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main2);

        imageView = (ImageView) findViewById(R.id.iv_image);
        //使用Bitmap工厂把图片加载进来
        Bitmap bitmap = BitmapFactory.decodeResource(getResources(), R.drawable.huaban);
        //创建一个空的图片，宽度和高度 还有信息跟原图片一样
        copyBitmap = Bitmap.createBitmap(bitmap.getWidth(), bitmap.getHeight(), bitmap.getConfig());
        //创建画笔
        paint = new Paint();
        //创建一个画布
        canvas = new Canvas(copyBitmap);
        //开始画画
        canvas.drawBitmap(bitmap, new Matrix(), paint);
        imageView.setImageBitmap(copyBitmap);

        //图片的触摸事件
        imageView.setOnTouchListener(new View.OnTouchListener() {
            @Override
            public boolean onTouch(View v, MotionEvent event) {
                //获取动作的事件
                int action = event.getAction();
                switch (action) {
                    case MotionEvent.ACTION_DOWN:
                        //按下事件
                        startX = event.getX();
                        startY = event.getY();
                        Log.e("按下", startX + "," + startY);
                        break;
                    case MotionEvent.ACTION_MOVE:
                        //滑动事件
                        float x = event.getX();
                        float y = event.getY();
                        //在画布上画直线，不能画点，滑动事件获得的坐标不是连续的
                        canvas.drawLine(startX, startY, x, y, paint);
                        //更新图片
                        imageView.setImageBitmap(copyBitmap);
                        startX = x;
                        startY = y;
                        Log.e("滑动", x + "," + y);
                        break;
                    case MotionEvent.ACTION_UP:
                        //抬起事件
                        float upX = event.getX();
                        float upY = event.getY();
                        Log.e("抬起", upX + "," + upY);
                        break;
                }
                //必须设置为true，否则只执行按下事件
                return true;
            }
        });

    }

    //修改画笔的颜色
    public void changeColor(View view) {
        paint.setColor(Color.RED);
    }

    //设置画笔的粗细
    public void bold(View view) {
        paint.setStrokeWidth(5);
    }

    //保存图片
    public void save(View view) {
        //创建一个图片的文件
        File file = new File(Environment.getExternalStorageDirectory(), System.currentTimeMillis() + ".png");
        FileOutputStream straeam;
        try {
            straeam = new FileOutputStream(file);
            //生成图片，参数①为图片的类型，参数②为图片质量，参数③为文件输出流
            copyBitmap.compress(Bitmap.CompressFormat.PNG, 100, straeam);
            Toast.makeText(this, "保存成功", Toast.LENGTH_SHORT).show();
        } catch (FileNotFoundException e) {
            e.printStackTrace();
        }
    }
}