在C＃中安全地處理Excel互操作對象？

Question

我正在開發一個winforms c＃visual studio 2008應用程序。 該應用程序與excel文件對話，我正在使用Microsoft.Office.Interop.Excel; 去做這個。

我想知道即使出現錯誤，如何確保釋放對象？

這是我的代碼：

private void button1_Click(object sender, EventArgs e)
{
    string myBigFile="";
    OpenFileDialog openFileDialog1 = new OpenFileDialog();
    DialogResult result = openFileDialog1.ShowDialog(); // Show the dialog.
    if (result == DialogResult.OK) // Test result.
        myBigFile=openFileDialog1.FileName;

    Excel.Application xlApp;
    Excel.Workbook xlWorkBook;
    Excel.Worksheet xlWorkSheet;
    Excel.Range range;

    string str;
    int rCnt = 0;
    int cCnt = 0;

    xlApp = new Excel.ApplicationClass();
    xlWorkBook = xlApp.Workbooks.Open(myBigFile, 0, true, 5, "", "", true, Microsoft.Office.Interop.Excel.XlPlatform.xlWindows, "\t", true, false, 0, true, 1, 0);
    xlWorkSheet = (Excel.Worksheet)xlWorkBook.Worksheets.get_Item(1);

    range = xlWorkSheet.UsedRange;

    /*
    for (rCnt = 1; rCnt <= range.Rows.Count; rCnt++)
    {
        for (cCnt = 1; cCnt <= range.Columns.Count; cCnt++)
        {
            str = (string)(range.Cells[rCnt, cCnt] as Excel.Range).Value2;
            MessageBox.Show(str);
        }
    }
     */
    xlWorkSheet..EntireRow.Delete(Excel.XLDirection.xlUp)

    xlWorkBook.SaveAs(xlWorkBook.Path + @"\XMLCopy.xls",         Excel.XlFileFormat.xlXMLSpreadsheet, Type.Missing, Type.Missing,
   false, false, Excel.XlSaveAsAccessMode.xlNoChange,
   Type.Missing, Type.Missing, Type.Missing, Type.Missing, Type.Missing);

    xlWorkBook.Close(true, null, null);
    xlApp.Quit();

    releaseObject(xlWorkSheet);
    releaseObject(xlWorkBook);
    releaseObject(xlApp);
}

private void releaseObject(object obj)
{
    try
    {
        System.Runtime.InteropServices.Marshal.ReleaseComObject(obj);
        obj = null;
    }
    catch (Exception ex)
    {
        obj = null;
        MessageBox.Show("Unable to release the Object " + ex.ToString());
    }
    finally
    {
        GC.Collect();
    }
}

我怎么能確保即使我在工作簿打開后得到一個錯誤，我確保處理對象：

Excel.Application xlApp;
Excel.Workbook xlWorkBook;
Excel.Worksheet xlWorkSheet;
Excel.Range range;

換句話說，無論我需要以下幾行來運行

xlWorkBook.Close(true, null, null);
xlApp.Quit();

releaseObject(xlWorkSheet);
releaseObject(xlWorkBook);
releaseObject(xlApp);

請注意，我也試過這個，導致同樣的問題

xlWorkBook.Close(false, System.Reflection.Missing.Value, System.Reflection.Missing.Value);


                xlApp.Quit();

                Marshal.ReleaseComObject(xlWorkSheet);
                Marshal.ReleaseComObject(xlWorkBook);
                Marshal.ReleaseComObject(xlApp);

                xlWorkSheet = null;
                xlWorkBook = null;
                xlApp = null;

                GC.GetTotalMemory(false);
                GC.Collect();
                GC.WaitForPendingFinalizers();
                GC.Collect();
                GC.GetTotalMemory(true);  

我也是這樣做的：

GC.Collect()                   ;
                GC.WaitForPendingFinalizers();
                GC.Collect()                  ; 
                GC.WaitForPendingFinalizers();

                Marshal.FinalReleaseComObject(xlWorkSheet);

                xlWorkBook.Close(Type.Missing, Type.Missing, Type.Missing);
                Marshal.FinalReleaseComObject(xlWorkBook); 

                xlApp.Quit();
                Marshal.FinalReleaseComObject(xlApp); 

在這一點上我不認為有可能從Visual Studio 2008關閉excel。它必須是一個bug或者什么，但我已經嘗試了前20個網站並得到相同的結果：excel因某種原因打開了兩個實例當我做垃圾收集等..（或不）它只關閉一個實例。

當我嘗試打開文件時，它表示存在錯誤或已損壞。

當我去任務管理器並殺死excel進程時，文件將打開沒有問題。]

有沒有辦法用visual studio 2008關閉excel？ 如果是的話，請你為我提供指導或解決方案

Answer 1

首先，我將介紹一個修改過的releaseObject ，然后我將提供一個模式來使用它。

using Marshal = System.Runtime.InteropServices.Marshal;
private void releaseObject(ref object obj) // note ref!
{
    // Do not catch an exception from this.
    // You may want to remove these guards depending on
    // what you think the semantics should be.
    if (obj != null && Marshal.IsComObject(obj)) {
        Marshal.ReleaseComObject(obj);
    }
    // Since passed "by ref" this assingment will be useful
    // (It was not useful in the original, and neither was the
    //  GC.Collect.)
    obj = null;
}

現在，使用的模式：

private void button1_Click(object sender, EventArgs e)
{
    // Declare. Assign a value to avoid a compiler error.
    Excel.Application xlApp = null;
    Excel.Workbook xlWorkBook = null;
    Excel.Worksheet xlWorkSheet = null;

    try {
        // Initialize
        xlApp = new Excel.ApplicationClass();
        xlWorkBook = xlApp.Workbooks.Open(myBigFile, 0, true, 5, "", "", true, Microsoft.Office.Interop.Excel.XlPlatform.xlWindows, "\t", true, false, 0, true, 1, 0);
        // If the cast fails this like could "leak" a COM RCW
        // Since this "should never happen" I wouldn't worry about it.
        xlWorkSheet = (Excel.Worksheet)xlWorkBook.Worksheets.get_Item(1);
        ...
    } finally {
        // Release all COM RCWs.
        // The "releaseObject" will just "do nothing" if null is passed,
        // so no need to check to find out which need to be released.
        // The "finally" is run in all cases, even if there was an exception
        // in the "try". 
        // Note: passing "by ref" so afterwords "xlWorkSheet" will
        // evaluate to null. See "releaseObject".
        releaseObject(ref xlWorkSheet);
        releaseObject(ref xlWorkBook);
        // The Quit is done in the finally because we always
        // want to quit. It is no different than releasing RCWs.
        if (xlApp != null) {
            xlApp.Quit();
        }
        releaseObject(ref xlApp);    
    }
}

在大多數情況下，可以擴展/嵌套這種簡單的方法。 我使用實現IDisposable的自定義包裝器類來簡化此任務。

Answer 2

驗證您在代碼中看到的兩個問題：

• 當程序關閉時，Excel仍然是一個正在運行的進程
• 當您打開Excel程序創建的Excel文件時，您會在Excel中看到錯誤，說文件已損壞或其他類似文件

我將編輯過的問題中的button1單擊處理程序和pst的releaseObject方法復制到一個干凈的VS2008，C＃3.5 Winform應用程序中，並進行了一些小的更改，以消除上面列出的問題。

要修復Excel不從內存中卸載，請在您創建的range對象上調用releaseObject 。 在調用releaseObject(xlWorkSheet);之前執行此操作releaseObject(xlWorkSheet); 記住所有這些參考資料是COM Interop編程非常有趣的原因。

要修復損壞的Excel文件的問題更新WorkBook.SaveAs方法調用替換第二個參數（ Excel.XlFileFormat.xlXMLSpreadsheet含） Type.Missing 。 默認情況下， SaveAs方法將正確處理此問題。

我確信您在問題中發布的代碼已經過簡化，以幫助調試您遇到的問題。 你應該使用try..finally塊pst演示。