简单的双缓冲画板

最新推荐文章于 2024-09-09 16:32:09 发布

转载最新推荐文章于 2024-09-09 16:32:09 发布 · 458 阅读

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#自定义View

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本文介绍了一个自定义Android View的实现方式，该View能够响应触摸事件并绘制路径。通过继承View并重写onMeasure、onTouchEvent和onDraw等方法，实现了一个简单的绘图功能。文章详细展示了如何创建和初始化Paint、Path等对象，并处理触摸事件来绘制连续的线条。

public class DrawView extends View {

    private Paint myPaint;
    private Bitmap myBitmap;
    private Canvas myCanvas;
    private Path myPath;
    //    private int width;
//    private int height;
    private int silentX;
    private int silentY;

    public DrawView(Context context) {
        this(context, null);
    }

    public DrawView(Context context, AttributeSet attrs) {
        this(context, attrs, 0);
    }

    public DrawView(Context context, AttributeSet attrs, int defStyleAttr) {
        super(context, attrs, defStyleAttr);

        init();
    }

    private void init() {

        myPaint = new Paint();
        myPath = new Path();
//        width,height的值在onMeasure之前无法得到，因此myBitmap的创建不能早于onMeasure
//        myBitmap = Bitmap.createBitmap(width, height, Bitmap.Config.ARGB_8888);
//        myCanvas = new Canvas(myBitmap);
        myPaint.setAntiAlias(true);
        myPaint.setDither(true);
        myPaint.setStyle(Paint.Style.STROKE);
        myPaint.setStrokeJoin(Paint.Join.ROUND); // 连接处平滑圆角
        myPaint.setStrokeCap(Paint.Cap.ROUND); // 画笔的样式为圆角
        myPaint.setStrokeWidth(20);// 设置画笔宽度

    }

    @Override
    protected void onMeasure(int widthMeasureSpec, int heightMeasureSpec) {
        super.onMeasure(widthMeasureSpec, heightMeasureSpec);
        int width = MeasureSpec.getSize(widthMeasureSpec);
        int height = MeasureSpec.getSize(heightMeasureSpec);

        /*或者
        int width = getMeasuredWidth();
        int height = getMeasuredHeight();*/
        myBitmap = Bitmap.createBitmap(width, height, Bitmap.Config.ARGB_8888);
        myCanvas = new Canvas(myBitmap);
    }

    @Override
    public boolean onTouchEvent(MotionEvent event) {
        int x = (int) event.getX();
        int y = (int) event.getY();
        switch (event.getAction()) {
            case MotionEvent.ACTION_DOWN:
                silentX = x;
                silentY = y;
                myPath.moveTo(silentX, silentY);
                break;
            case MotionEvent.ACTION_MOVE:
                int dx = Math.abs(x - silentX);
                int dy = Math.abs(y - silentY);//
                //  滑动超过一定距离才进行更新
                if (dx > 3 || dy > 3) {
                    myPath.lineTo(x, y);
                    silentX = x;
                    silentY = y;
                    invalidate();
                }
                break;
        }
        return true;
    }

    @Override
    protected void onDraw(Canvas canvas) {
        drawPath();
        canvas.drawBitmap(myBitmap, 0, 0, null);
    }

    private void drawPath() {
        myCanvas.drawPath(myPath, myPaint);
    }
}