返回类型必须是 'bool' 错误

Question

我使用 xamarin android 创建了需要显示和警告框的应用程序，并根据选择的值进行一些计算。所以在菜单项点击我已经添加了下面的代码。

public override async Task<bool> OnOptionsItemSelected(IMenuItem item)
{
    bool bTotalResult = false;
    switch (item.ItemId)
    {


        case Resource.Id.action_next:
            bTotalResult = await ShowPayMentTypeDialog();

            return await Task.Run(() => true).ConfigureAwait(true); ;
        default:
            return await Task.Run(() => base.OnOptionsItemSelected(item)).ConfigureAwait(true);;
    }
    //return await Task.Run(() => false ).ConfigureAwait(true);
}
private async Task<bool> ShowPayMentTypeDialog()
{
    bool bResult = false;
    try
    {
        LayoutInflater layoutInflater = LayoutInflater.From(this);
        View view = layoutInflater.Inflate(Resource.Layout.lyt_cash_credit_popup, null);
        Android.Support.V7.App.AlertDialog.Builder alertbuilder = new Android.Support.V7.App.AlertDialog.Builder(this);
        alertbuilder.SetView(view);
        var userdata = view.FindViewById<Spinner>(Resource.Id.spnrPaymentTerms);
        List<cls_spinner_adapter> resultsWayNo = new List<cls_spinner_adapter> {
        new cls_spinner_adapter {SZ_SPINNER_TEXT ="CASH"},
       new cls_spinner_adapter {SZ_SPINNER_TEXT ="CREDIT" } };
        CommonSpinnerAdapter paymentAdapter = new CommonSpinnerAdapter(this, resultsWayNo);
        userdata.Adapter = paymentAdapter;
        alertbuilder.SetCancelable(false)
        .SetPositiveButton("OK", delegate
        {
            if (resultsWayNo[userdata.SelectedItemPosition].SZ_SPINNER_TEXT == "CASH")
            {
                cls_statics.B_IS_PROMOMAYMANET_CASH = true;
            }
            else
            {
                cls_statics.B_IS_PROMOMAYMANET_CASH = false;
            }
            bResult = true;
        })
        .SetNegativeButton("Cancel", delegate
        {
            cls_statics.B_IS_PROMOMAYMANET_CASH = false;
            bResult = true;
            alertbuilder.Dispose();

        });
        Android.Support.V7.App.AlertDialog dialog = alertbuilder.Create();
        dialog.Show();
    }
    catch
    {

    }
    return await Task.Run(() => bResult).ConfigureAwait(true);
}

但是在编译时我遇到了错误。

返回类型必须为 'bool' 以匹配被覆盖的成员 Activity.OnOptionsItemSelected(IMenuItem)

Answer 1

贴出的代码有几个问题，我们来看看。

1. 正如编译器告诉您的那样，您无法更改要覆盖的方法的签名。因此，将您的方法更改为：

   override bool OnOptionsItemSelected
   

2. .ConfigureAwait(true);是默认配置，不需要显式调用。

3. 以下行不必要地启动一个新的线程池线程，只是为了返回一个常量值：

   return await Task.Run(() => true)
   

   该代码应该只是：

   return true;
   

4. 不应将同步代码标记为异步以尝试使其异步。相反，如果需要，调用者必须以异步方式调用它们。您应该熟悉 Stephen Cleary 的这篇优秀文章：Task.Run Etiquette Examples: Don't Use Task.Run in the Implementation。

所以，让我们把所有这些放在一起：

//Point 1
public override bool OnOptionsItemSelected(IMenuItem item)
{
    bool bTotalResult = false;

    switch (item.ItemId)
    {
        case Resource.Id.action_next:
            bTotalResult = Task.Run(() => ShowPayMentTypeDialog()).Result;

            // point 3
            return true;
        default:
            // point 3
            return base.OnOptionsItemSelected(item);
    }
}

// point 4
private bool ShowPayMentTypeDialog()
{
    bool bResult = false;
    try
    {
        LayoutInflater layoutInflater = LayoutInflater.From(this);
        View view = layoutInflater.Inflate(Resource.Layout.lyt_cash_credit_popup, null);
        Android.Support.V7.App.AlertDialog.Builder alertbuilder = new Android.Support.V7.App.AlertDialog.Builder(this);
        alertbuilder.SetView(view);
        var userdata = view.FindViewById<Spinner>(Resource.Id.spnrPaymentTerms);
        List<cls_spinner_adapter> resultsWayNo = new List<cls_spinner_adapter> {
        new cls_spinner_adapter {SZ_SPINNER_TEXT ="CASH"},
       new cls_spinner_adapter {SZ_SPINNER_TEXT ="CREDIT" } };
        CommonSpinnerAdapter paymentAdapter = new CommonSpinnerAdapter(this, resultsWayNo);
        userdata.Adapter = paymentAdapter;
        alertbuilder.SetCancelable(false)
        .SetPositiveButton("OK", delegate
        {
            if (resultsWayNo[userdata.SelectedItemPosition].SZ_SPINNER_TEXT == "CASH")
            {
                cls_statics.B_IS_PROMOMAYMANET_CASH = true;
            }
            else
            {
                cls_statics.B_IS_PROMOMAYMANET_CASH = false;
            }
            bResult = true;
        })
        .SetNegativeButton("Cancel", delegate
        {
            cls_statics.B_IS_PROMOMAYMANET_CASH = false;
            bResult = true;
            alertbuilder.Dispose();

        });
        Android.Support.V7.App.AlertDialog dialog = alertbuilder.Create();
        dialog.Show();
    }
    catch
    {

    }

    // point 3
    return bResult;
}