C#傳遞帶有引數的Func，其中1個引數在傳遞時設定，其他引數在內部設定

您好，已經創建了這個方法來從 excel 中讀取資料：

        public static Dictionary<int, TreeItemModel> ExcelReader(FileUploadModel upload,
            Func<Dictionary<int, string>, Row, object, Action> func)
        {
            try
            {
                var dict = new Dictionary<int, TreeItemModel>();
                using (var doc = SpreadsheetDocument.Open(upload.Stream, false))
                {
                    var workbookPart = doc.WorkbookPart;

                    var worksheetPart = workbookPart.WorksheetParts.First();

                    var sheetData = worksheetPart.Worksheet.Elements<SheetData>().First();

                    var stringTable = LoadSharedStringDictionarySax(workbookPart.SharedStringTablePart);

                    foreach (var r in sheetData.Elements<Row>())
                    {
                        func(stringTable, r, dict);
                    }
                }

                upload.Stream.Close();

                upload.UploadCompletion = 100;

                return dict;
            }
            catch (Exception ex)
            {
                System.Diagnostics.Debug.WriteLine(ex.Message);

                throw;
            }
        }        

我在其他類中呼叫這個方法是這樣的：

private async Task OnFilesDropped(FileUploadModel upload)
{
    var dict = new Dictionary<int, TreeItemModel>();

    OfficeHelper.ExcelExtension.ExcelReader(upload, ExcelToProjTree);
}

private static Action ExcelToProjTree(Dictionary<int, string> stringTable, Row r, Dictionary<int, TreeItemModel> dict)
{
  //Some stuff
}

stringTable 和 r 在呼叫方法時設定，但我想在呼叫 ExcelReader 時設定字典

就像這樣：

private async Task OnFilesDropped(FileUploadModel upload)
{
    var dict = new Dictionary<int, TreeItemModel>();

    OfficeHelper.ExcelExtension.ExcelReader(upload, () => ExcelToProjTree(dict));
}

是否可以？如果是，如何？

uj5u.com熱心網友回復：

由于您將提供一個靜態object引數引數（這稱為部分應用順便說一句），您需要從結果Func型別的引數串列中洗掉它：

public static Dictionary<int, TreeItemModel> ExcelReader(FileUploadModel upload,
        Func<Dictionary<int, string>, Row, Action> func) { /* */ }

然后確保您作為引數提供的 lambda 也ExcelReader具有正確的簽名（它仍然應該接受Dictionary<int, string>和Row引數）：

OfficeHelper.ExcelExtension.ExcelReader(upload, (stringTable, row) => ExcelToProjTree(stringTable, row, dict));

最后更新函式的呼叫，以便只傳遞前兩個引數：

func(stringTable, r); // `dict` will automatically be bound inside of `func`

鑒于func仍然回傳Action，您可能想立即呼叫它：

func(stringTable, r)();

uj5u.com熱心網友回復：

您可以使用 Lazy<T>

private Lazy<Dictionary<int, TreeItemModel>> dict;

// Constructor
public YourClass()
{
    this.dict = Lazy<Dictionary<int, TreeItemModel>>(
        () => ExcelToProjTree(new Dictionary<int, TreeItemModel>()));
}

private async Task OnFilesDropped(FileUploadModel upload)
{
    var dict = new Dictionary<int, TreeItemModel>();

    // ExcelToProjTree Will be eveluated only now
    OfficeHelper.ExcelExtension.ExcelReader(upload, () => dict.Value);
}

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