Question

vb中API函数findwindow的详细用法

Answer 1

vb中FindWindow函数可以用来返回窗体的句柄。
1、VB6.0中的API声明:
Private Declare Function FindWindow Lib "user32" Alias "FindWindowA" (ByVal lpClassName As String, ByVal lpWindowName As String) As Long
2、具体使用：
dim i as long
i=FindWindow（vbNullString，"窗体的标题"）
注意：这里的vbNullString是空的，没有任何字符，即不传递。和""空字符串是不一样的！
3、例子：
有一个标题名字是计算器的窗体或软件，获取这个计算器的句柄
Option Explicit
Private Declare Function FindWindow Lib "user32" Alias "FindWindowA" (ByVal lpClassName As String, ByVal lpWindowName As String) As Long
Private Sub Command1_Click()
Dim i As Long
i = FindWindow(vbNullString, "计算器")
msgbox& i '显示窗体句柄
End sub

Answer 2

就是按照窗口的类名和标题查找顶层窗口。

微软官方说法如下：

The FindWindow function retrieves a handle to the top-level window
whose class name and window name match the specified strings. This function does
not search child windows. This function does not perform a case-sensitive
search.

To search child windows, beginning with a specified child window, use the
FindWindowEx
function.

Syntax
HWND FindWindow(
LPCTSTR lpClassName,
LPCTSTR lpWindowName
);

Parameters

lpClassName
[in] Pointer to a null-terminated string that specifies the class name or a
class atom created by a previous call to the RegisterClass or
RegisterClassEx
function. The atom must be in the low-order word of lpClassName; the
high-order word must be zero.
If lpClassName points to a string, it specifies the window class name.
The class name can be any name registered with RegisterClass or
RegisterClassEx, or any of the predefined control-class names.

If lpClassName is NULL, it finds any window whose title matches the
lpWindowName parameter.

lpWindowName
[in] Pointer to a null-terminated string that specifies the window name (the
window's title). If this parameter is NULL, all window names match.

追问

这为什么不对？

追答

Private Declare Function FindWindow Lib "user32" Alias "FindWindowA" (ByVal lpClassName As Long, ByVal lpWindowName As String) As Long

a = FindWindow(0, "计算器")

api所要求的NULL值和空字符串不是一回事和，需要传一个0进去。

追问

怎么修改窗体标题？用SetWindowText和FindWindow

追答

Private Declare Function SetWindowText Lib "user32" Alias "SetWindowTextA" (ByVal hwnd As Long, ByVal lpString As String) As Long

    Dim a As Long
    a = FindWindow(0, "计算器")
    If a = 0 Then
        MsgBox "未运行"
    Else
        MsgBox "运行"
        SetWindowText a, "改过的计算器"
    End If