xamarinform框架里面下拉框值的判断，例如两个（1，2）下拉框获取的值都是一样（ABCDE）的如何判断，当下拉框1选择了A,下拉框B就不能选（后台方法）!
前端： <StackLayout>
<Label Text="起始位置" FontSize="Medium" />
<Picker x:Name="StartLocPicker" Title="请选择起始位置" SelectedItem="{Binding StartLoc, Mode=TwoWay}"></Picker>
<Label Text="目的位置" FontSize="Medium" />
<Picker x:Name="EndLocPicker" Title="请选择目的位置" SelectedItem="{Binding EndLoc, Mode=TwoWay}"></Picker>
<Button x:Name="HandOutBtn" Text="任务下发" Command="{Binding HandTaskCommand}" FontAttributes="Bold"></Button>
<Label Text="{Binding Message}" FontSize="16" TextColor="blue"/>
</StackLayout>
后面只写了下拉框绑定，已经成功，不会写判断，希望大佬指点一下这个判断方法，咋写
public TaskIssuePage()
{
InitializeComponent();
ResultEntity result = new ResultEntity { ResultCode = 1 };

        try
        {
            ////起始位置
            WMSContainer mCon = new WMSContainer();
            result = AgvApiHelper.CallEmiApi("GetStationNameList", JsonConvert.SerializeObject(mCon));
            if (result.ResultCode != 1)
                throw new Exception(result.ResultMsg.ToString());
            List<WMSContainer> items = JsonConvert.DeserializeObject<List<WMSContainer>>(result.ResultMsg.ToString());
            foreach (var item in items)
            {
                string text = item.StationName.Trim();
                StartLocPicker.Items.Add(text);
            }
            ////目的位置
            //result = AgvApiHelper.CallEmiApi("GetStationNameList", JsonConvert.SerializeObject(mCon));
            //items = JsonConvert.DeserializeObject<List<WMSContainer>>(result.ResultMsg);

            foreach (var item in items)
            {
                string text = item.StationName.Trim();

                EndLocPicker.Items.Add(text);
            }

            //if (StartLocPicker = bool.Parse(mCon.StationName))
            //{
            //    if(EndLocPicker== StartLocPicker)
            //    {
            //        return false;
            //    }
            //    return StartLocPicker;
            //}
        }
        catch (Exception ex)
        {
            throw new Exception(ex.Message);
        }

        BindingContext = _viewModel = new TaskIssueViewModel();
    }