Question

我收到错误：

无法将类型'System.Data.DataTable'隐式转换为'System.Threading.Tasks.Task'

GetExternalMessage 正在执行Time，因此WinForm停止响应。因此我想到了应用“任务等待”。但我仍然得到错误。我们如何在Task中返回dataTable？

以下是我正在尝试的代码：

private void button1_Click(object sender, EventArgs e)
{
    dtFrom.Format = DateTimePickerFormat.Short;
    dtTo.Format = DateTimePickerFormat.Short;
    DataTable dt = new DataTable();
    //dt =  GetExtMsg(dtFrom.Text, dtTo.Text);

}

async Task<DataTable> GetExtMsg(string dateFrom, string dateTo)
{
    DL dl = new DL();
    DataTable dt = new DataTable();
    dt =  dl.GetExternalMessage(dateFrom, dateTo);
    Task<DataTable> tastDT = dt;

}

Answer 1

正如错误所述，您无法隐式（或明确地）将DataTable转换为Task<DataTable>。

来自MSDN：

You specify Task<TResult> as the return type of an async method if the return statement of the method specifies an operand of type TResult.

因此，您应该从方法中返回DataTable对象，如下所示：

async Task<DataTable> GetExtMsg(string dateFrom, string dateTo)
{
 DL dl = new DL();
 DataTable dt = new DataTable();
 dt =  dl.GetExternalMessage(dateFrom, dateTo);
 return dt;
}

要使用此async方法，您应该在方法名称前使用await关键字，如下所示：

private async void button1_Click(object sender, EventArgs e)
{
 dtFrom.Format = DateTimePickerFormat.Short;
 dtTo.Format = DateTimePickerFormat.Short;
 DataTable dt = new DataTable();
 dt = await GetExtMsg(dtFrom.Text, dtTo.Text);
}

无法将“DataTable”隐式转换为“Task <datatable>”</datatable>

1 个答案: