c# - 无法将 'DataTable' 隐式转换为 'Task'

Question

我收到错误:

Cannot implicitly convert type 'System.Data.DataTable' to 'System.Threading.Tasks.Task'

GetExternalMessage 需要时间来执行，因此 WinForm 停止响应。因此我想到了应用“任务等待”。但我仍然收到错误。我们如何在 Task 中返回一个 dataTable？

下面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

如错误所述，您不能隐式(或显式)转换 DataTable到 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.

因此你应该只返回 DataTable像这样从你的方法中对象:

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

消费这个async方法，你应该使用 await方法名称前的关键字，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);
}