在按下后退按钮上显示操作表

Question

我正在使用PCL创建xamarin表单。我想在用户从移动设备硬件按后退按钮时提供一项功能，然后我想DispalyActionSheet.我可以这样做的任何选择。下面是我的示例代码。

    protected override bool OnBackButtonPressed()
    {
        base.OnBackButtonPressed();
        //new thread
        Device.BeginInvokeOnMainThread(async () =>
        {
              var action = await DisplayActionSheet("ActionSheet: Send to?", "Cancel", null, "Facebook", "twitter", "Instagram");
      //  Here i want to get  action  result for next step
        });
        return true; // 
    }

根据Martin Zikmund的建议进行代码更新：代码执行后在不同页面上重定向时感到困难

 protected override bool OnBackButtonPressed()
        {
            bool returnvalue = true;
            Device.BeginInvokeOnMainThread(async () =>
            {
              vawait DisplayActionSheet("ActionSheet: Send to?", "null", null, "Facebook", "twitter", "Instagram");
                    switch (action)
                    {
                        case "Facebook":
                         // My code
                CallPage();  Here i want to redirect on different page 
               break;
                    }
            });
      }

 public async void CallPage()
    {
        try
        {
            await RetrunToPreviousPage();
        }
        catch (Exception ex)
        {
            //throw;
        }
    }
  public async Task<dynamic> RetrunToPreviousPage()
    {
            Navigation.InsertPageBefore(new InboundOrderList(), this);
            await Navigation.PopAsync();            
        return true;
    }

Answer 1

如果要

自己处理后退按钮，则需要删除对base.OnBackButtonPressed的调用。

protected override bool OnBackButtonPressed()
{        
    Device.BeginInvokeOnMainThread(async () =>
    {
          var action = await DisplayActionSheet(
            "ActionSheet: Send to?", "Cancel", null, "Facebook", "twitter", "Instagram");
          //your logic             
    });
    return true; //you handled the back button press
}

当您实际上想在逻辑中导航回时，您必须手动弹出堆栈的页面：

await this.Navigation.PopAsync();

更新

您仍然必须在OnBackButtonPressed结束时返回true以将其标记为已处理。此外，ReturnToPreviousPage不需要任何return true;，返回类型可以是一个简单的Task：

protected override bool OnBackButtonPressed()
    {
        bool returnvalue = true;
        Device.BeginInvokeOnMainThread(async () =>
        {
          vawait DisplayActionSheet("ActionSheet: Send to?", "null", null, "Facebook", "twitter", "Instagram");
                switch (action)
                {
                    case "Facebook":
                     // My code
            CallPage();  Here i want to redirect on different page 
           break;
                }
        });
      return true; // always return true
  }
  ...
  public async Task RetrunToPreviousPage()
  { 
      Navigation.InsertPageBefore(new InboundOrderList(), this);
      await Navigation.PopAsync();            
  }