问题日记:VC MFC 鼠标移动画矩形

昨天的时候，模仿人家的软件已经七七八八啦，开始不断完善的工作。首先是完善用鼠标拖动矩形选择东西,开始当然进入死胡同，在OnMouseMove里单纯画矩形，结果测试移动一下鼠标杯了,n个矩形刺瞎了我的眼:



我相信人家做得到的，我也做得到，只是我还不知道而已。于是上网找资料,虽说网上有很多资料,可也有点费时,有时看了资料测试还不一定行，汗,不行你放上网干嘛啦。最后结果OK啦:



现写下来：
（1 ）在类里定义变量和消息:
bool m_bClickEmpty; //判断是否点击了空白的地方，以实现拖动框选择

CPoint OldEmptyBegin;//点击空白开始的座标

CPoint NowEmptyEnd;//移动时保存座标

afx_msg void OnMouseMove(UINT nFlags, CPoint point);afx_msg void OnLButtonDown(UINT nFlags, CPoint point);afx_msg void OnLButtonUp(UINT nFlags, CPoint point);

( 2 )在鼠标相关的消息里面写代码:

void XX::OnLButtonDown(UINT nFlags, CPoint point){

m_bClickEmpty = true;

OldEmptyBegin =
point;

NowEmptyEnd =
point;

}

void XX::OnMouseMove(UINT nFlags, CPoint point)

{

if ( m_bClickEmpty ) { CClientDC dc(this);

CBrush *pBrush = CBrush::FromHandle( (HBRUSH)GetStockObject( NULL_BRUSH) );

CBrush *POldBrush = dc.SelectObject( pBrush );

int nOldMode = dc.SetROP2(R2_NOTXORPEN);

dc.Rectangle( &CRect( OldEmptyBegin, NowEmptyEnd ) );

dc.Rectangle( &CRect( OldEmptyBegin, point ) );

NowEmptyEnd = point;

dc.SelectObject( POldBrush );

dc.SetROP2( nOldMode );

}

}

void XX::OnLButtonUp(UINT nFlags, CPoint point){

if ( m_bClickEmpty ) { m_bClickEmpty = false;

CClientDC dc(this);

CBrush *pBrush = CBrush::FromHandle( (HBRUSH)GetStockObject( NULL_BRUSH) );

CBrush *POldBrush = dc.SelectObject( pBrush );

int nOldMode = dc.SetROP2(R2_NOTXORPEN);

dc.Rectangle( &CRect( OldEmptyBegin, NowEmptyEnd ) );

dc.SelectObject( POldBrush );

dc.SetROP2( nOldMode );

}}

有时候最好还是让鼠标限制在一个的主框里面这样会比较好办（座标，鼠标不用走到外面，在外面也没用）,用ClipCursor.

-----------------------------+_+------------------2013-05-28

上面都是老方法了，叫橡皮筋技术，但是在不停拖动过程中还是会出现一些难看的重绘，应该用双缓冲，保存鼠标点击下去时候的点StartPoint，和鼠标移动时候的点EndPoint，直接刷新界面。这样更好.

CPoint m_StartPoint;//开始点

CPoint m_EndPoint;//结束点

BOOL m_bLBDown;//鼠标是否按下

afx_msg void OnLButtonDown(UINT nFlags, CPoint point);
afx_msg void OnLButtonUp(UINT nFlags, CPoint point);
afx_msg void OnMouseMove(UINT nFlags, CPoint point);
afx_msg BOOL OnEraseBkgnd(CDC* pDC);

m_bLBDown = FALSE;//在构造函数初始化为FALSE

void CMy22Dlg::OnPaint()
{
CPaintDC dc(this);

//绘制背景
CRect rect;
GetClientRect(&rect);

CBrush bruDB(RGB(255, 255, 255));//背景颜色

dc.FillRect(&rect, &bruDB);

//绘制拖动矩形
if (m_bLBDown)
{
CRect rect(m_StartPoint, m_EndPoint);

rect.NormalizeRect();//规范化矩形

CBrush bruPen(RGB(255, 0, 0));//矩形边框颜色

dc.FrameRect(&rect, &bruPen);
}
}

void CMy22Dlg::OnLButtonDown(UINT nFlags, CPoint point)
{
m_StartPoint = point;

m_EndPoint = point;

m_bLBDown = TRUE;

SetCapture();//设置鼠标捕获

CDialogEx::OnLButtonDown(nFlags, point);
}

void CMy22Dlg::OnLButtonUp(UINT nFlags, CPoint point)
{
if(this == GetCapture())
{
ReleaseCapture();
}

m_bLBDown = FALSE;

Invalidate(FALSE);//更新界面

CDialogEx::OnLButtonUp(nFlags, point);
}

void CMy22Dlg::OnMouseMove(UINT nFlags, CPoint point)
{
if (m_bLBDown)
{
m_EndPoint = point;

Invalidate(FALSE);//更新界面
}

CDialogEx::OnMouseMove(nFlags, point);
}

BOOL CMy22Dlg::OnEraseBkgnd(CDC* pDC)
{
//return CDialogEx::OnEraseBkgnd(pDC);不需要重绘背景
return TRUE;
}