关于MEASUREITEMSTRUCT的itemData

最新推荐文章于 2020-11-21 11:28:30 发布

原创最新推荐文章于 2020-11-21 11:28:30 发布 · 1.1k 阅读

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文章标签：

#application #menu #string #list #null

本文介绍了使用Visual C++进行菜单自绘的过程，特别是在重写菜单重绘函数时如何利用自定义结构实现菜单项数据的存储与读取。通过具体代码示例展示了如何正确设置和解析菜单项的数据。

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在VC范例宝典中有绘制图标菜单的实例，在重写的重绘菜单函数中有这么几句

...

m_iteminfo = (CMenuItemInfo*)lpStruct->itemData;

//lpStruct是LPMEASUREITEMSTRUCT类型或LPDRAWITEMSTRUCT

//CMenuItemInfo是自定义的结构
lpStruct->itemWidth = ((CMenuItemInfo*)lpStruct->itemData)->m_ItemText.GetLength()*10;
switch(m_iteminfo->m_ItemID)//m_iteminfo是自定义的结构，itemData与其相符吗

...

刚开始还奇怪系统给的结构怎么可以转成自定义的？？

后找到答案，

先看关于itemData的说明

itemData

For a combo box or list box, this member contains the value that was passed to the list box by one of the following:

CComboBox::AddString

CComboBox::InsertString

CListBox::AddString

CListBox::InsertString

For a menu, this member contains the value that was passed to the menu by one of the following:

CMenu::AppendMenu

CMenu::InsertMenu

CMenu::ModifyMenu

发现程序前面是用ModifyMenu来修改菜单来着，再找它：

BOOL ModifyMenu( UINT nPosition, UINT nFlags, UINT nIDNewItem = 0, LPCTSTR lpszNewItem = NULL );

在其函数参数中有lpszNewItem，说明如下

lpszNewItem

Specifies the content of the new menu item. The nFlags parameter can be used to interpret lpszNewItem in the following ways:

nFlags	Interpretation of lpszNewItem
MF_OWNERDRAW	Contains an application-supplied 32-bit value that the application can use to maintain additional data associated with the menu item. This 32-bit value is available to the application when it processes MF_MEASUREITEM and MF_DRAWITEM.
MF_STRING	Contains a long pointer to a null-terminated string or to a CString.
MF_SEPARATOR	The lpszNewItem parameter is ignored (not needed).