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gbianchi
Asked: 2020-10-12 07:56:30 +0800 CST 2020-10-12 07:56:30 +0800 CST

How to make a grid select the first record if it depends on another grid

  • 772

I have a model, of the form:

public class A
{
   public ObservableCollection B col1;
}

Public Class B
{
   public int BA;
   public int BB;
   public ObservableCollection C;
}

public Class C
{
   public int CA;
   public int CB;
}

The first DataGrid is filled with the content of A, which is nothing more than a list of B elements.

<DataGrid x:Name="GrillaA" AutoGenerateColumns="False" IsReadOnly="True" SelectionMode="Single" ItemsSource="{Binding Mode=OneWay}">
   <DataGrid.Columns>
       <DataGridTextColumn Binding="{Binding BA}"/>
       <DataGridTextColumn Binding="{Binding BB}"/>
   </DataGrid.Columns>
 </DataGrid>

And then I have another grid, which is filled with the content of the list that contains B (the list of objects C)

<DataGrid x:Name="GrillaB" AutoGenerateColumns="False" IsReadOnly="True" SelectionMode="Single" ItemsSource="{Binding SelectedItem.C, ElementName=GrillaA}">
   <DataGrid.Columns>
       <DataGridTextColumn Binding="{Binding CA}"/>
       <DataGridTextColumn Binding="{Binding CB}"/>
   </DataGrid.Columns>
</DataGrid>

All this is going perfectly... except that under each grid I have some text boxes that are filled with the content of the selected row in the grid... In the case of the first grid, I have no problem, they fill perfectly...

The question is: when I select an item in GridA, how do I select the first element of GridB, in an MVVM model, in such a way that the fields below that grid are filled?

EDITION

I leave an example in git:

https://github.com/topcatarg/MVVMGridsTest

and no, beyond the first screen, on the second screen when selecting an item from the first grid, the second grid does not select the first item (because the selection property is executed twice)

c#

1 Answers

  1. Best Answer

    What you should do is add the property SelectedIndexwith properties of your View Model to your grids, both in GridA and GridB:

    <DataGrid x:Name="GrillaA" AutoGenerateColumns="True" IsReadOnly="True" SelectionMode="Single" ItemsSource="{Binding Lista2}" SelectedIndex="{Binding SelectedA,Mode=TwoWay,UpdateSourceTrigger=PropertyChanged}"/>

<DataGrid Grid.Column="1" x:Name="GrillaB" AutoGenerateColumns="True" IsReadOnly="True" SelectionMode="Single" ItemsSource="{Binding Lista2}" SelectedIndex="{Binding SelectedB,Mode=TwoWay,UpdateSourceTrigger=PropertyChanged}"/>

    So in your ViewModel you add the two properties, and in the setter of the first one (which will be executed when the selected index changes in GrillaA) you will be able to change the index of the other grid:

    public class ViewModel:INotifyPropertyChanged
{
    public event PropertyChangedEventHandler PropertyChanged;

    private int _selectedA=-1;
    private int _selectedB=-1;
    public int SelectedA
    {
        get { return this._selectedA; }
        set
        {
            this._selectedA = value;
            this.SelectedB = 0;
            NotifyPropertyChanged();
        }
    }

    public int SelectedB
    {
        get { return this._selectedB; }
        set
        {
            this._selectedB = value;
            NotifyPropertyChanged();
        }

    }

    private void NotifyPropertyChanged([CallerMemberName] String propertyName = "")
    {
        if (PropertyChanged != null)
        {
            PropertyChanged(this, new PropertyChangedEventArgs(propertyName));
        }
    }
}

    This is a possible solution, there are others but I usually go for this one.

    edited

    I will present another solution, since when using a property of SelectedItemthe first grid to load the ItemsSourcesecond one, the first proposed solution did not work correctly.

    First, we must add the dependency property to gridB in the binding of , ItemsSourceso that we are notified when the . Afterwards, we simply subscribe to the gridB event and select the first index there. Example:NotifyOnTargetUpdatedtrueItemsSourceTargetUpdated

    XAML:

    <DataGrid x:Name="dgListaB" ItemsSource="{Binding ListaB}"/>
<DataGrid x:Name="dgListaC" Grid.Row="2" ItemsSource="{Binding SelectedItem.ListaC, ElementName=dgListaB,NotifyOnTargetUpdated=True}" TargetUpdated="dgListaC_TargetUpdated"/>

    Event handler:

    private void dgListaC_TargetUpdated(object sender, DataTransferEventArgs e)
{
    this.dgListaC.SelectedIndex = 0;
}
    • 3