Method being passed entire list instead of specific element

Question

Method being passed entire list instead of specific element

BigSlug 21

Firstly I apologise; my knowledge of xamarin and c# is non-existent therefore I'm going to butcher the terminology here.

My view "OrderReturnView.xaml" looks like this;

The plus (+) button for each line is defined as per;

OrderReturnView.xaml;

<!-- PLUS BUTTON -->  
<Button   
    Grid.Row="0" Grid.Column="6"   
    IsVisible="{Binding IsPlusButtonEnabled}"  
    IsEnabled="{Binding IsActionable}"  
    Style="{StaticResource PlusMinusButton}" Text="+"   
    Command="{Binding Path=BindingContext.PlusCommand, Source={x:Reference Name=ThisPage}}"  
    CommandParameter="{Binding .}"/>

ReturnViewModel.cs;

Upon clicking "+" the "obj" passed to the command is the specific line that had the "+" clicked;

I added "ShowReturnReasonCodeDialog" to the plus command - this just sets the "IsVisible" bound bools to "true" to display the reason code selection popup. The user then selects a reason code from a drop down and clicks confirm.

Excerpt of the popup definitions, specifically the "confirm" button which is what I'm having problems with;

OrderReturnView.xaml (added a template with visibility controlled via a bool value);

<!-- RETURN REASON CODE SELECTION POPUP GRID -->  
<templates:ReturnReasonCodeDialog   
    Grid.Column="0"  
    Grid.Row="0"  
    Grid.ColumnSpan="3"  
    Grid.RowSpan="7"  
    IsVisible="{Binding ReturnReasonCodePopupVisibility}" />

ReturnReasonCodeDialog.xaml template the popup's "confirm" button definition;

<ContentView xmlns="http://xamarin.com/schemas/2014/forms"   
             xmlns:x="http://schemas.microsoft.com/winfx/2009/xaml"  
             xmlns:i18n="clr-namespace:Xfulfilment.Helpers;assembly=Xfulfilment"  
             x:Class="Xfulfilment.Templates.ReturnReasonCodeDialog"  
             x:Name="ThisPage">  
...  
	<Button IsEnabled="{Binding IsActionable}"  
			Style="{StaticResource AcceptButton}"  
			Text="{i18n:Translate confirm_button}"  
			Padding="0,0,0,0"  
			Margin="5,0,10,0"  
			VerticalOptions="Center"  
			HorizontalOptions="Start"   
			Command="{Binding Path=BindingContext.ConfirmReasonCodePopupCommand, Source={x:Reference Name=ThisPage}}"  
			CommandParameter="{Binding .}"/>

ViewModel;

The issue here is that when "confirm" is clicked the data passed to "obj" is the entire collection of lines;

Whereas I just want the line that had the "+" clicked on it just before the popup was shown. I am guessing the problem here is something to do my Command/CommandParameter definitions for the confirm button however having had a read up on them I'm still unsure what I need to do - any ideas?

Michael Taylor 61,106 Reputation points

2022-09-07T17:57:26.45+00:00

You didn't post the code for ShowReturnReasonCodeDialog so we will just be guessing here. The problem seems to be that you didn't set the data context of your XAML dialog so it is defaulting to the parent window's context which is the entire list. Ensure the dialog's data context is the line that is selected and it should work correctly. Note that in many cases a window view model has a "selected" property that exposes the selected item. If you have that then you can bind it directly to the dialog in the XAML (probably). Otherwise you'll need to programmatically change the data context before you show the dialog.
BigSlug 21 Reputation points

2022-09-08T08:53:18.55+00:00

I didn't include the code cause I said it just sets the bool values so didn't seem relevant;

Would you be able to give an example of either using the view model's "selected" property or programmatically changing the "data context", please?
Michael Taylor 61,106 Reputation points

2022-09-08T14:27:27.707+00:00
OK, then it seems like you just need to adjust your CommandParameter in your XAML to pass the correct object instead of the entire parent view model. It looks like your dialog is probably parented to the window and not the row in the grid. Because of this the . is referencing the parent model and not the row model.

I think the easiest approach, without seeing all your XAML is to expose a SelectedLine property from your order return view model.

public class OrderReturnViewModel { public ReturnOrderDetailLine SelectedLine { get; set; } }

Bind the property in your grid's XAML (assuming you're using DataGrid).

<DataGrid SelectedItem="{Binding Path=SelectedLine, Mode=TwoWay}" ... />

Then use that value as the command parameter.

<Button IsEnabled="{Binding IsActionable}"... Command="{Binding Path=BindingContext.ConfirmReasonCodePopupCommand, Source={x:Reference Name=ThisPage}}" CommandParameter="{Binding SelectedLine}"/>

Finally get the value.

protected void OnConfirmReasonCodePopupCommand ( object obj ) { var line = obj as ReturnOrderLineDetail; if (line != null) { }; }
BigSlug 21 Reputation points

2022-09-08T15:41:08.253+00:00
@Michael Taylor - Thanks for taking the time to get back to me (for some reason I can't post this as a comment...)

The lines on the screen are defined within a listview bound to "ReturnLines";

OrderReturnViewModel.cs (for some reason if I include C# code the "preview" and "submit" buttons don't work);

OrderReturnView.xaml;

<ListView Grid.Row="5" Grid.Column="1" VerticalOptions="FillAndExpand" HorizontalOptions="FillAndExpand" ItemsSource="{Binding ReturnLines}" CachingStrategy="RecycleElement" SeparatorVisibility="Default" SeparatorColor="{StaticResource BackGroundGrey}" VerticalScrollBarVisibility="Never" BackgroundColor="White" HasUnevenRows="True" SelectionMode="None" > <ListView.Header.../> <ListView.ItemTemplate.../> </ListView>

As per your suggestion; I added the relevant items and modified the view but "SelectedLine" is never set so the passed in parm to OnConfirmReasonCodePopupCommand is null.

I tried removing the "SelectionMode" = "None" but that didn't make a difference, also had a google for doing using SelectedItem with ListView but couldn't find anything relevant - most of the examples I found where were items being selected from a list but in this case the list is displayed and the only interaction is the +/- buttons so is it the case that nothing is actually being selected?

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Michael Taylor 61,106 Reputation points

2022-09-07T17:57:26.45+00:00

You didn't post the code for ShowReturnReasonCodeDialog so we will just be guessing here. The problem seems to be that you didn't set the data context of your XAML dialog so it is defaulting to the parent window's context which is the entire list. Ensure the dialog's data context is the line that is selected and it should work correctly. Note that in many cases a window view model has a "selected" property that exposes the selected item. If you have that then you can bind it directly to the dialog in the XAML (probably). Otherwise you'll need to programmatically change the data context before you show the dialog.
BigSlug 21 Reputation points

2022-09-08T08:53:18.55+00:00

I didn't include the code cause I said it just sets the bool values so didn't seem relevant;

Would you be able to give an example of either using the view model's "selected" property or programmatically changing the "data context", please?
Michael Taylor 61,106 Reputation points

2022-09-08T14:27:27.707+00:00

OK, then it seems like you just need to adjust your CommandParameter in your XAML to pass the correct object instead of the entire parent view model. It looks like your dialog is probably parented to the window and not the row in the grid. Because of this the . is referencing the parent model and not the row model.

I think the easiest approach, without seeing all your XAML is to expose a SelectedLine property from your order return view model.

public class OrderReturnViewModel { public ReturnOrderDetailLine SelectedLine { get; set; } }

Bind the property in your grid's XAML (assuming you're using DataGrid).

<DataGrid SelectedItem="{Binding Path=SelectedLine, Mode=TwoWay}" ... />

Then use that value as the command parameter.

<Button IsEnabled="{Binding IsActionable}"... Command="{Binding Path=BindingContext.ConfirmReasonCodePopupCommand, Source={x:Reference Name=ThisPage}}" CommandParameter="{Binding SelectedLine}"/>

Finally get the value.

protected void OnConfirmReasonCodePopupCommand ( object obj ) { var line = obj as ReturnOrderLineDetail; if (line != null) { }; }
BigSlug 21 Reputation points

2022-09-08T15:41:08.253+00:00

@Michael Taylor - Thanks for taking the time to get back to me (for some reason I can't post this as a comment...)

The lines on the screen are defined within a listview bound to "ReturnLines";

OrderReturnViewModel.cs (for some reason if I include C# code the "preview" and "submit" buttons don't work);

OrderReturnView.xaml;

<ListView Grid.Row="5" Grid.Column="1" VerticalOptions="FillAndExpand" HorizontalOptions="FillAndExpand" ItemsSource="{Binding ReturnLines}" CachingStrategy="RecycleElement" SeparatorVisibility="Default" SeparatorColor="{StaticResource BackGroundGrey}" VerticalScrollBarVisibility="Never" BackgroundColor="White" HasUnevenRows="True" SelectionMode="None" > <ListView.Header.../> <ListView.ItemTemplate.../> </ListView>

As per your suggestion; I added the relevant items and modified the view but "SelectedLine" is never set so the passed in parm to OnConfirmReasonCodePopupCommand is null.

I tried removing the "SelectionMode" = "None" but that didn't make a difference, also had a google for doing using SelectedItem with ListView but couldn't find anything relevant - most of the examples I found where were items being selected from a list but in this case the list is displayed and the only interaction is the +/- buttons so is it the case that nothing is actually being selected?

Answer 1

Michael Taylor 61,106

Ok so you are using a list view but you aren't actually selecting the item in the list. In that case selection isn't going to work as you aren't using it. At this point I think you have a couple of options. Before calling ShowReturnReasonCodeDialog set the view model's SelectedLine property to the line item.

   if (String.IsNullOrWhiteSpace(returnDetailLine.ReasonCode))  
   {  
      SelectedLine = returnDetailLine;  
      ShowReturnReasonCodeDialog();  
   }

The alternative would be to pass the returnDetailLine to ShowReturnReasonCodeDialog and have it do something similar.

BigSlug 21 Reputation points

2022-09-08T16:29:54.07+00:00

You, good xir, are a sanity saver - this has been driving me insane for 2 days. This works exactly as I need it to, thank you so much.

If you post it as an answer and I'll accept it.
Michael Taylor 61,106 Reputation points

2022-09-08T17:02:10.087+00:00

Done.

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Method being passed entire list instead of specific element

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