Android中在屏幕上涂鸦的例子

在这个例子中自定义了一个View，可以接受touch动作，然后在屏幕上即时的显示出touch的轨迹，类似于线条的屏幕上涂鸦。这个例子主要是演示如何将onTouchEvent与draw配合起来使用。在这个基础上，可以做很多有用的程序。

import android.content.Context;
import android.graphics.Canvas;
import android.graphics.Color;
import android.graphics.Paint;
import android.graphics.Path;
import android.graphics.Paint.Style;
import android.view.MotionEvent;
import android.view.View;
 
/**
 * Example for hand writing.
 *
 * @author http://www.android-study.com/jiemiansheji/285.html
 * @version 2010/09/07
 *
 */
public class HandwritingView extends View {
    private Paint paint = null;
    private Path path = null;
 
    public HandwritingView(Context context) {
        super(context);
        path = new Path();
        paint = new Paint();
        paint.setColor(Color.YELLOW);
        paint.setStyle(Style.STROKE);
        paint.setAntiAlias(true);
        this.setBackgroundColor(Color.BLACK);
    }
 
    @Override
    public boolean onTouchEvent(MotionEvent event) {
        if (event.getAction() == MotionEvent.ACTION_DOWN) {
            int x = (int) event.getX();
            int y = (int) event.getY();
            path.moveTo(x, y);
            invalidate();
            return true;
        } else if (event.getAction() == MotionEvent.ACTION_MOVE) {
            int x = (int) event.getX();
            int y = (int) event.getY();
            path.lineTo(x, y);
            invalidate();
            return true;
        }
        return super.onTouchEvent(event);
    }
 
    @Override
    protected void onDraw(Canvas canvas) {
        super.onDraw(canvas);
        if (path != null) {
            canvas.drawPath(path, paint);
        }
    }
}