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#2
bczgvip2014-05-31 10:24
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代码如下
程序代码：Option Explicit
Private Declare Function MoveToEx Lib "gdi32" (ByVal hdc As Long, ByVal x As Long, ByVal y As Long, lpPoint As Long) As Long
Private Declare Function LineTo Lib "gdi32" (ByVal hdc As Long, ByVal x As Long, ByVal y As Long) As Long
Private Sub Command1_Click()
Dim drawhdc As Long
Dim ret As Long
drawhdc = Me.hdc
Debug.Print drawhdc
Debug.Print MoveToEx(Me.hdc, 10, 10, 0&)
Debug.Print LineTo(Me.hdc, 100, 10)
Debug.Print MoveToEx(drawhdc, 10, 10, 0&)
Debug.Print drawhdc
Debug.Print LineTo(drawhdc, 10, 100)
Me.Refresh
End Sub
Private Declare Function MoveToEx Lib "gdi32" (ByVal hdc As Long, ByVal x As Long, ByVal y As Long, lpPoint As Long) As Long
Private Declare Function LineTo Lib "gdi32" (ByVal hdc As Long, ByVal x As Long, ByVal y As Long) As Long
Private Sub Command1_Click()
Dim drawhdc As Long
Dim ret As Long
drawhdc = Me.hdc
Debug.Print drawhdc
Debug.Print MoveToEx(Me.hdc, 10, 10, 0&)
Debug.Print LineTo(Me.hdc, 100, 10)
Debug.Print MoveToEx(drawhdc, 10, 10, 0&)
Debug.Print drawhdc
Debug.Print LineTo(drawhdc, 10, 100)
Me.Refresh
End Sub
打印的结果：
1593906163
1
1
1
10
0
可以看到drawhdc已经从 1593906163被修改为10，导致最后一次LineTo函数的调用失败。
如果 一直用Me.hdc做参数的话，有时会导致vb的崩溃，无法捕捉任何错误信息。
更加奇怪的事情是，如果在Dim drawhdc As Long 后面再声明一个变量Dim ret As Long，那就完全正确了。
崩溃啊