FileInfo.Exists 屬性

定義

命名空間:

System.IO

組件:

System.Runtime.dll

來源:

FileInfo.cs

取得值，這個值指出檔案是否存在。

public:
 virtual property bool Exists { bool get(); };

public override bool Exists { get; }

member this.Exists : bool

Public Overrides ReadOnly Property Exists As Boolean

屬性值

Boolean

如果檔案存在，則為 true；如果檔案不存在或者檔案是目錄，則為 false。

範例

下列程式代碼範例會使用 屬性， Exists 確保檔案存在，再開啟它。 當找不到檔案時，您可以使用這項技術擲回自定義例外狀況。

array<Byte>^ Openfile(String^ fileName)
{
    // Check the fileName argument.
    if (fileName == nullptr || fileName->Length == 0)
    {
        throw gcnew ArgumentNullException("fileName");
    }

    // Check to see if the file exists.
    FileInfo^ fInfo = gcnew FileInfo(fileName);

    // You can throw a personalized exception if
    // the file does not exist.
    if (!fInfo->Exists)
    {
        throw gcnew FileNotFoundException("The file was not found.",
            fileName);
    }

    try
    {
        // Open the file.
        FileStream^ fStream = gcnew FileStream(fileName, FileMode::Open);

        // Create a buffer.
        array<Byte>^ buffer = gcnew array<Byte>(fStream->Length);

        // Read the file contents to the buffer.
        fStream->Read(buffer, 0, (int)fStream->Length);

        // return the buffer.
        return buffer;
    }
    catch (IOException^ ex)
    {
        Console::WriteLine(ex->Message);
        return nullptr;
    }
}

public byte[] OpenDataFile(string FileName)
{
    // Check the FileName argument.
    if (FileName == null || FileName.Length == 0)
    {
        throw new ArgumentNullException("FileName");
    }

    // Check to see if the file exists.
    FileInfo fInfo = new FileInfo(FileName);

    // You can throw a personalized exception if
    // the file does not exist.
    if (!fInfo.Exists)
    {
        throw new FileNotFoundException("The file was not found.", FileName);
    }

    // Open the file.
    FileStream fStream = new FileStream(FileName, FileMode.Open);

    // Create a buffer.
    byte [] buffer = new byte[fStream.Length];

    // Read the file contents to the buffer.
    fStream.Read(buffer, 0, (int)fStream.Length);

    // return the buffer.
    return buffer;
}

Function OpenDataFile(ByVal FileName As String) As Byte()
    ' Check the FileName argument.
    If FileName Is Nothing OrElse FileName.Length = 0 Then
        Throw New ArgumentNullException("FileName")
    End If

    ' Check to see if the file exists.
    Dim fInfo As New FileInfo(FileName)

    ' You can throw a personalized exception if 
    ' the file does not exist.
    If Not fInfo.Exists Then
        Throw New FileNotFoundException("The file was not found.", FileName)
    End If

    ' Open the file.
    Dim fStream As New FileStream(FileName, FileMode.Open)

    ' Create a buffer.
    Dim buffer(fStream.Length) As Byte

    ' Read the file contents to the buffer.
    fStream.Read(buffer, 0, Fix(fStream.Length))

    ' return the buffer.
    Return buffer

End Function

備註

第一次呼叫時， FileInfo 呼叫 Refresh 並快取檔案的相關信息。 在後續呼叫時，您必須呼叫 Refresh 以取得最新的資訊複本。

如果嘗試判斷指定的檔案是否存在，屬性 Exists 會傳回 false 如果發生任何錯誤。 這可能會在引發例外狀況的情況下發生，例如傳遞無效字元或太多字元的檔名、失敗或遺失的磁碟，或呼叫端沒有讀取檔案的許可權。

另請參閱

• 檔案和資料流 I/O
• 作法：讀取檔案中的文字
• 作法：將文字寫入檔案