OpenFileDlg 範例
這個範例示範如何呼叫 Unmanaged 函式，其預期含有字串之結構的指標。 此外，它也示範如何使用 Managed 類別來表示 Unmanaged 結構、如何套用 InAttribute 和 OutAttribute 屬性來封送處理類別回呼叫端，以及如何宣告和初始化類別的不同欄位來產生正確的 Unmanaged 表示。
OpenFileDlg 範例使用下列 Unmanaged 函式，顯示其原始函式宣告：
從 Comdlg32.dll 匯出 GetOpenFileName。
BOOL GetOpenFileName(LPOPENFILENAME lpofn);
傳遞至前一個函式之 Win32 API 的 LPOPENFILENAME 結構包含下列項目：
typedef struct tagOFN {
DWORD lStructSize;
//…
LPCTSTR lpstrFilter;
//…
LPTSTR lpstrFile;
DWORD nMaxFile;
LPTSTR lpstrFileTitle;
DWORD nMaxFileTitle;
LPCTSTR lpstrInitialDir;
LPCTSTR lpstrTitle;
//…
LPCTSTR lpstrDefExt;
//…
} OPENFILENAME, *LPOPENFILENAME;
在這個範例中，OpenFileName 類別包含原始結構的元素做為類別成員。 Unmanaged 結構是宣告為類別而非 Managed 結構，來顯示當 Unmanaged 函式預期結構的指標時，類別如何使用類別。 因為 Managed 類別是參考型別 (Reference Type)，當它是以傳值方式傳遞時，類別的指標會被傳遞至 Unmanaged 程式碼。 這正是 Unmanaged 函式所預期的。
套用 StructLayoutAttribute 屬性以確保成員是按照出現的順序，循序配置於記憶體中。 設定 CharSet 欄位，以便平台叫用可以根據目標平台在 Run Time 於 ANSI 和 Unicode 格式間選擇。
LibWrap 類別包含 GetOpenFileName 方法的 Managed 原型，會將 OpenFileName 類別當成 In/Out 參數傳遞。 在這個範例中，透過明確套用 InAttribute 和 OutAttribute，可以確保將 OpenFileName 封送處理為 In/Out 參數，而呼叫端可以查看封送處理回的變更 (由於效能因素，類別的預設方向屬性是 In，避免呼叫端查看封送處理回的變更)。App 類別會建立 OpenFileName 類別的新執行個體，並使用 Marshal.SizeOf 方法決定 Unmanaged 結構的大小 (以位元組為單位)。
宣告原型
' Declare a class member for each structure element.
<StructLayout(LayoutKind.Sequential, CharSet:=CharSet.Auto)> _
Public Class OpenFileName
Public structSize As Integer = 0
Public hwnd As IntPtr = IntPtr.Zero
Public hinst As IntPtr = IntPtr.Zero
Public filter As String = Nothing
Public custFilter As String = Nothing
Public custFilterMax As Integer = 0
Public filterIndex As Integer = 0
Public file As String = Nothing
Public maxFile As Integer = 0
Public fileTitle As String = Nothing
Public maxFileTitle As Integer = 0
Public initialDir As String = Nothing
Public title As String = Nothing
Public flags As Integer = 0
Public fileOffset As Short = 0
Public fileExtMax As Short = 0
Public defExt as String = Nothing
Public custData As Integer = 0
Public pHook As IntPtr = IntPtr.Zero
Public template As String = Nothing
End Class
Public Class LibWrap
' Declare managed prototype for the unmanaged function.
Declare Auto Function GetOpenFileName Lib "Comdlg32.dll" ( _
<[In], Out> ByVal ofn As OpenFileName ) As Boolean
End Class
// Declare a class member for each structure element.
[StructLayout(LayoutKind.Sequential, CharSet=CharSet.Auto)]
public class OpenFileName
{
public int structSize = 0;
public IntPtr hwnd = IntPtr.Zero;
public IntPtr hinst = IntPtr.Zero;
public string filter = null;
public string custFilter = null;
public int custFilterMax = 0;
public int filterIndex = 0;
public string file = null;
public int maxFile = 0;
public string fileTitle = null;
public int maxFileTitle = 0;
public string initialDir = null;
public string title = null;
public int flags = 0;
public short fileOffset = 0;
public short fileExtMax = 0;
public string defExt = null;
public int custData = 0;
public IntPtr pHook = IntPtr.Zero;
public string template = null;
}
public class LibWrap
{
// Declare a managed prototype for the unmanaged function.
[DllImport("Comdlg32.dll", CharSet=CharSet.Auto)]
public static extern bool GetOpenFileName([In, Out] OpenFileName ofn);
}
// Declare a class member for each structure element.
[StructLayout(LayoutKind::Sequential, CharSet=CharSet::Auto)]
public ref class OpenFileName
{
public:
int structSize;
IntPtr hwnd;
IntPtr hinst;
String^ filter;
String^ custFilter;
int custFilterMax;
int filterIndex;
String^ file;
int maxFile;
String^ fileTitle;
int maxFileTitle;
String^ initialDir;
String^ title;
int flags;
short fileOffset;
short fileExtMax;
String^ defExt;
int custData;
IntPtr pHook;
String^ tmplate;
OpenFileName()
{
// Initialize the fields.
for each (FieldInfo^ fi in this->GetType()->GetFields())
{
fi->SetValue(this, nullptr);
}
}
};
public ref class LibWrap
{
public:
// Declare a managed prototype for the unmanaged function.
[DllImport("Comdlg32.dll", CharSet=CharSet::Auto)]
static bool GetOpenFileName([In, Out] OpenFileName^ ofn);
};
呼叫函式
Public Class App
Public Shared Sub Main()
Dim ofn As New OpenFileName()
ofn.structSize = Marshal.SizeOf(ofn)
ofn.filter = "Log files" & ChrW(0) & "*.log" & ChrW(0) & _
"Batch files" & ChrW(0) & "*.bat" & ChrW(0)
ofn.file = New String(New Char(256){})
ofn.maxFile = ofn.file.Length
ofn.fileTitle = new string(New Char(64){})
ofn.maxFileTitle = ofn.fileTitle.Length
ofn.initialDir = "C:\"
ofn.title = "Open file called using platform invoke..."
ofn.defExt = "txt"
If LibWrap.GetOpenFileName(ofn) Then
Console.WriteLine("Selected file with full path: {0}", ofn.file)
End If
End Sub
End Class
public class App
{
public static void Main()
{
OpenFileName ofn = new OpenFileName();
ofn.structSize = Marshal.SizeOf(ofn);
ofn.filter = "Log files\0*.log\0Batch files\0*.bat\0";
ofn.file = new string(new char[256]);
ofn.maxFile = ofn.file.Length;
ofn.fileTitle = new string(new char[64]);
ofn.maxFileTitle = ofn.fileTitle.Length;
ofn.initialDir = "C:\\";
ofn.title = "Open file called using platform invoke...";
ofn.defExt = "txt";
if (LibWrap.GetOpenFileName(ofn))
{
Console.WriteLine("Selected file with full path: {0}", ofn.file);
}
}
}
public ref class App
{
public:
static void Main()
{
OpenFileName^ ofn = gcnew OpenFileName();
ofn->structSize = Marshal::SizeOf(ofn);
ofn->filter = "Log files\0*.log\0Batch files\0*.bat\0";
ofn->file = gcnew String(gcnew array<Char>(256));
ofn->maxFile = ofn->file->Length;
ofn->fileTitle = gcnew String(gcnew array<Char>(64));
ofn->maxFileTitle = ofn->fileTitle->Length;
ofn->initialDir = "C:\\";
ofn->title = "Open file called using platform invoke...";
ofn->defExt = "txt";
if (LibWrap::GetOpenFileName(ofn))
{
Console::WriteLine("Selected file with full path: {0}", ofn->file);
}
}
};
請參閱
概念
其他資源
Creating Prototypes in Managed Code