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POWhy OnVScroll() method enters only once?
 

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  1. POWhy OnVScroll() method enters only once?
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    <p>I design a class which derives from CScrollBar in a dialog-based MFC application. In the dialog class (MyScrollbarDlg), I set the <strong>ON_WM_VSCROLL</strong> message and declare the <strong>OnVSCroll</strong> method in the header file. I also Implement the OnVScroll() method in the corresponding .cpp file. But to my surprise, when I click the arrow at the buttom of of the scrollbar, it only did its work at the first time. </p> <p>I want to debug my code, so I set a break point in the OnVScroll method. Then strange thing happened. The break point was only arrived at the first click. When I continue, the scrollbar disappeared from the dialog! I've no idea how this could happen. Could anyone help me to fix this annoying bug? Thank you very much!</p> <p>I have set the scroll range like below:</p> <pre><code> SCROLLINFO scrllInfo; m_scrollbar.GetScrollInfo(&amp;scrllInfo, SIF_ALL); scrllInfo.nMax = 15; scrllInfo.nMin = 0; scrllInfo.nPage = 0; scrllInfo.nPos = 0; m_scrollbar.SetScrollInfo(&amp;scrllInfo, TRUE); </code></pre> <p>btw, I don't use the embedded scrollbar of the dialog, but a scrollbar control which set to be a member of the dialog.</p> <p>I did some experiment and found that the problem I mentioned only occurred when I click the arrow at the bottom of the scrollbar control. It acts well when I click the other arrow or drag the scroll box. Is there anything different when clicking the bottom arrow of a scrollbar which I am not aware of?</p> <p>I figured out that when the scroll message is NOT THUMBPOSITION or THUMBTRACK, the parameter <code>nPos</code> of <code>OnVScroll()</code> method is not used. So I changed my code like this:</p> <pre><code> int currPos = m_scrollbar.GetScrollPos(); m_scrollbar.SetScrollPos(currPos + 1, TRUE); </code></pre> <p>This time it acts normal, but if I set a break point, the scrollbar disappeared again. Do you know why?</p>
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    1. USHeena Goyal
    1. USuser26404
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      1. POWhy OnVScroll() method enters only once?
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    1. COplease stop giving comments to your own question in the form of answers. This isn't a forum. Just edit your original question, or comment on other answers.
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      1. USTheSoftwareJedi
 

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