<?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);
        // Load the image using the Bitmap factory
        Bitmap bitmap = BitmapFactory.decodeResource(getResources(), R.drawable.huaban);
        // Create an empty image with the same width, height, and configuration as the original image
        copyBitmap = Bitmap.createBitmap(bitmap.getWidth(), bitmap.getHeight(), bitmap.getConfig());
        // Create a paintbrush
        paint = new Paint();
        // Create a canvas
        canvas = new Canvas(copyBitmap);
        // Start drawing
        canvas.drawBitmap(bitmap, new Matrix(), paint);
        imageView.setImageBitmap(copyBitmap);

        // Image touch event
        imageView.setOnTouchListener(new View.OnTouchListener() {
            @Override
            public boolean onTouch(View v, MotionEvent event) {
                // Get the action type of the event
                int action = event.getAction();
                switch (action) {
                    case MotionEvent.ACTION_DOWN:
                        // Press event
                        startX = event.getX();
                        startY = event.getY();
                        Log.e("Pressed", startX + "," + startY);
                        break;
                    case MotionEvent.ACTION_MOVE:
                        // Swipe event
                        float x = event.getX();
                        float y = event.getY();
                        // Draw a straight line on the canvas (can't draw just a point; the coordinates from the swipe event are not continuous)
                        canvas.drawLine(startX, startY, x, y, paint);
                        // Update the image
                        imageView.setImageBitmap(copyBitmap);
                        startX = x;
                        startY = y;
                        Log.e("Swipe", x + "," + y);
                        break;
                    case MotionEvent.ACTION_UP:
                        // Release event
                        float upX = event.getX();
                        float upY = event.getY();
                        Log.e("Released", upX + "," + upY);
                        break;
                }
                // Must return true to ensure only the down event is triggered
                return true;
            }
        });

    }

    // Modify the color of the paintbrush
    public void changeColor(View view) {
        paint.setColor(Color.RED);
    }

    // Set the thickness of the paintbrush
    public void bold(View view) {
        paint.setStrokeWidth(5);
    }

    // Save the image
    public void save(View view) {
        // Create a file for the image
        File file = new File(Environment.getExternalStorageDirectory(), System.currentTimeMillis() + ".png");
        FileOutputStream stream;
        try {
            stream = new FileOutputStream(file);
            // Generate the image: parameter ① image type, parameter ② image quality, parameter ③ file output stream
            copyBitmap.compress(Bitmap.CompressFormat.PNG, 100, stream);
            Toast.makeText(this, "Saved successfully", Toast.LENGTH_SHORT).show();
        } catch (FileNotFoundException e) {
            e.printStackTrace();
        }
    }
}