5月2日学习日志

今天学习了简单的画板的制作。

代码为：

public class MyView extends View{

    private Paint mPaint;  //绘制线条的Path
    private Path mPath;      //记录用户绘制的Path
    private Canvas mCanvas;  //内存中创建的Canvas
    private Bitmap mBitmap;  //缓存绘制的内容

    private int mLastX;
    private int mLastY;

    public MyView(Context context) {
        super(context);
        init();
    }

    public MyView(Context context, AttributeSet attrs) {
        super(context, attrs);
        init();
    }

    public MyView(Context context, AttributeSet attrs, int defStyleAttr) {
        super(context, attrs, defStyleAttr);
        init();
    }

    private void init(){
        mPath = new Path();
        mPaint = new Paint();   //初始化画笔
        mPaint.setColor(Color.GREEN);
        mPaint.setAntiAlias(true);
        mPaint.setDither(true);
        mPaint.setStyle(Paint.Style.STROKE);
        mPaint.setStrokeJoin(Paint.Join.ROUND); //结合处为圆角
        mPaint.setStrokeCap(Paint.Cap.ROUND); // 设置转弯处为圆角
        mPaint.setStrokeWidth(20);   // 设置画笔宽度
    }

    @Override
    protected void onMeasure(int widthMeasureSpec, int heightMeasureSpec) {
        super.onMeasure(widthMeasureSpec, heightMeasureSpec);
        int width = getMeasuredWidth();
        int height = getMeasuredHeight();
        // 初始化bitmap,Canvas
        mBitmap = Bitmap.createBitmap(width, height, Bitmap.Config.ARGB_8888);
        mCanvas = new Canvas(mBitmap);
    }

    //重写该方法，在这里绘图
    @Override
    protected void onDraw(Canvas canvas) {
        drawPath();
        canvas.drawBitmap(mBitmap, 0, 0, null);
    }

    //绘制线条
    private void drawPath(){
        mCanvas.drawPath(mPath, mPaint);
    }

    @Override
    public boolean onTouchEvent(MotionEvent event) {

        int action = event.getAction();
        int x = (int) event.getX();
        int y = (int) event.getY();

        switch (action)
        {
            case MotionEvent.ACTION_DOWN:
                mLastX = x;
                mLastY = y;
                mPath.moveTo(mLastX, mLastY);
                break;
            case MotionEvent.ACTION_MOVE:
                int dx = Math.abs(x - mLastX);
                int dy = Math.abs(y - mLastY);
                if (dx > 3 || dy > 3)
                    mPath.lineTo(x, y);
                mLastX = x;
                mLastY = y;
                break;
        }

        invalidate();
        return true;
    }
}