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Wpf MutliSelect DataGrid with custom datagrid

I'm aware that there are several posts about how to implement datagrid mutliselection.
I've found the open issue on Github (https://github.com/dotnet/wpf/issues/3140).
The user ice1e0 mentioned a solution with a CustomDataGrid class.
public class CustomDataGrid : DataGrid
{
public static readonly DependencyProperty SelectedItemsProperty = DependencyProperty.Register(nameof(SelectedItems), typeof(IList), typeof(CustomDataGrid), new PropertyMetadata(default(IList), OnSelectedItemsPropertyChanged));
protected override void OnSelectionChanged(SelectionChangedEventArgs e)
{
base.OnSelectionChanged(e);
SetValue(SelectedItemsProperty, base.SelectedItems);
}
public new IList SelectedItems
{
get => (IList)GetValue(SelectedItemsProperty);
set => throw new Exception("This property is read-only. To bind to it you must use 'Mode=OneWayToSource'.");
}
private static void OnSelectedItemsPropertyChanged(DependencyObject d, DependencyPropertyChangedEventArgs e)
{
((CustomDataGrid)d).OnSelectedItemsChanged((IList)e.OldValue, (IList)e.NewValue);
}
protected virtual void OnSelectedItemsChanged(IList oldSelectedItems, IList newSelectedItems)
{
}
}
So, I tried to implement it, so I copied the class.
And my xaml looks something like that:
<Project1:CustomDataGrid ItemsSource="{Binding Data}" SelectionMode="Extended" SelectionUnit="FullRow" IsReadOnly="True" SelectedItems="{Binding SelectedComputers, Mode=OneWayToSource}" />
and my ViewModel:
[ObservableProperty]
ObservableCollection<string> _selectedComputers;
I use CommunityToolkit.Mvvm (v8.0).
It compiles but SelectedComputers is null, after I select one or multiple items.
UPDATE:
The issue seems that
void CustomDataGrid_SelectionChanged(object sender, SelectionChangedEventArgs e)
{
this.SelectedItemsList = this.SelectedItems;
}
doesn't work. SelectedItemsList is always null. The problem is mentioned in the other thread: Select multiple items from a DataGrid in an MVVM WPF project
The suggested solution by M463:
this.SelectedItemsList = this.SelectedItems; did not work for me, as SelectedItemsList was always set to null. However, changing the code to foreach (var item in this.SelectedItems) { this.SelectedItemsList.Add(item); } did the trick. Please note, that this requires you to call this.SelectedItemsList.Clear(); in advance, so the items of SelectedItemsList will not get duplicated.
When I try the solution, after selected a row the application crashes with the error:
System.ArgumentException: 'The value "System.Data.DataRowView" is not of type "System.String" and cannot be used in this generic collection.
Parameter name: value'

You cannot mix types.
If you Data is a DataView, SelectedItems cannot be bound to an ObservableCollection<string> because you cannot add a (selected) DataRowView to an ObservableCollection<string>.
Also, you cannot set an ObservableCollection<string> property to anything else than an ObservableCollection<string>. That's why the value in the setter of the source property comes in as null when you try to set it to an IList using SetValue.
If you make SelectedComputers an IList, you should see it being set from the control:
[ObservableProperty]
IList _selectedComputers;
The other option is obviously to change the type of the dependency property.

How to filter ComboBox itemssource based on other ComboBox selected item in WPF-C#? [closed]

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I have a list of Clients and two ComboBox that named cmbList1, cmbList2.
Based on MVVM Model i create ObservableCollection for first list :
private ObservableCollection<Client> MyFirstList = new ObservableCollection<Client>();
public ObservableCollection<Client> myfirlist
{
get { return myfirlist; }
set
{
this.myfirlist=value;
NotifyPropertyChanged("myfirstlist");
}
}
and there is my second list i create for adding filtered first list.
private ObservableCollection<Client> myseclist = new ObservableCollection<Client>();
now how can i show this filtered in XAML and also how to filtered in code behind?

in your ViewModel, you create an ObservableCollection :
private ObservableCollection<Client> MyFirstList = new ObservableCollection<Client>();
public ObservableCollection<Client> myFirstList
{
get { return myFirstList; }
set
{
this.myFirstList=value;
NotifyPropertyChanged("MyFirstList");
}
}
Then you create an ICollectionView :
public ICollectionView MySecondListView { get; set; }
When you call your ViewModel, you need to "link" the view to the first list :
MySecondListView = CollectionViewSource.GetDefaultView(MyFirstList);
So MySecondListView will just be a "copy" of your First list.
STEP 2 : Filter
You need to bind selected element from the 1st ComboBox, and everytime its value changed, apply a filter to your ICollectionView :
private Client selectedClient = null;
public Client SelectedClient
{
get { return selectedClient; }
set
{
this.selectedClient = value;
this.NotifyPropertyChanged("SelectedClient");
MySecondListView.Filter=new Predicate<object>(GetFilteredView);
}
}
private bool getFilteredView(object obj)
{
Client client = (Client)obj;
if(this.SelectedClient!=null && client==this.SelectedClient) return false;
return true;
}
On that way, the second list will return the same as the 1st one, without selected item.
Then finally XAML :
<ComboBox x:Name="FirstComboBox" ItemsSource="{Binding MyFirstList}" DisplayMemberPath="Name" SelectedValuePath="ID" SelectedValue="{Binding SelectedClient, UpdateSourceTrigger=PropertyChanged}"/>
<ComboBox x:Name="SecondComboBox" ItemsSource="{Binding MySecondListView}" DisplayMemberPath="Name" SelectedValuePath="ID"/>
EDIT : Without MVVM :
In that case you can use ComboBox.SelectedIndex or ComboBox.SelectedItem and do something like that :
In your XAML use the event "SelectionChanged"
then you can make a function like that :
private void MyFirstComboBox_SelectionChanged(object sender, SelectionChangedEventArgs e)
{
MySecondList.Clear();
for(int i=0;i<MyFirstList.Count();i++)
{
if(i!=MyComboBox.SelectedIndex) MySecondList.Add(MyFirstList[i];
//if(MyFirstList[i]!=MyComboBox.SelectedItem) MySecondList.Add(MyFirstList[i];
}
}
But then you need to define 2 separated ObservableCollection.

How to get access viewcell by index from ListView object in xamarin forms?

I want to get Viewcell(view) of listview in xamarin forms by index, i tried a lot as below code
var myViewCellList = mListView.ItemTemplate.values;
//this return Dictionary with 0 elements
it may look like
var view = mListView.ItemTamplate[index];

I found the workaround to get the viewcell by passing item index, not the better way but this works if we dont have any alternate.
MyListView.NotifyRowTapped(selectedTimeCardIndex);
private void ViewCellTapped(object sender, EventArgs args)
{
if(sender is ViewCell viewCell)
{
//viewCell for the selected index
}
}

I just got solution of this problem by myself while using ITemplatedItemsView interface by customising the ListView
For more discussion visit Here
public class CustomViewCell: ListView
{
public ITemplatedItemsList<Cell> TemplatedItem
{
get { return ((ITemplatedItemsView<Cell>)this).TemplatedItems; }
}
}
Implementation :
var viewcell = (CustomViewCell.TemplatedItem[0] as viewcell);

Items in a listbox updating erratically WPF

I have a simple list of strings which I want to be displayed in a listbox depending on if a checkbox is checked when a button is pressed. I have this logic in my button listener:
private void fileSavePerms_Click(object sender, RoutedEventArgs e)
{
foreach (CheckBox checkbox in checkboxList)
{
if (checkbox.IsChecked == true && !permissionList.Contains(checkbox.Name))
{
permissionList.Add(checkbox.Name);
}
else if (checkbox.IsChecked == false && permissionList.Contains(checkbox.Name))
{
permissionList.Remove(checkbox.Name);
}
}
permListBox.ItemsSource = permissionList;
}
As far as I know, this is how you can do a very simple data-bind on button click. However the listbox updates for the first time as intended, but then will update with incorrect contents of the list I am trying to populate the box with. I can see no discernible pattern with the output.
Furthermore, after a while (a few button clicks), I will catch an exception saying "an ItemsControl is inconsistent with its items source".
Am I setting up my binding incorrectly or assigning the ItemsControl at the incorrect time?
Update:
The XAML for the list box:
<ListBox x:Name="permListBox" ItemsSource="{Binding permissionList}" HorizontalAlignment="Left" Height="36" Margin="28,512,0,0" VerticalAlignment="Top" Width="442"/>

First of all you can bind only properties to a control. A field cannot be bound. So permissionList must be a property of the DataContext object you set to your Window.DataContext property.
If this is correctly set then you can create a new List<string> every time and then assign it to the property bound to the control. You do not have to assign it to the ItemsSource property of the control
Let's say your window's data context is set to the window itself.
public partial class MainWindow : Window
{
public MainWindow()
{
InitializeComponent();
this.DataContext = this;
}
public List<string> PermissionList
{
get { return (List<string>)GetValue(PermissionListProperty); }
set { SetValue(PermissionListProperty, value); }
}
public static readonly DependencyProperty PermissionListProperty =
DependencyProperty.Register(
"PermissionList",
typeof(List<string>),
typeof(MainWindow),
new PropertyMetadata(new List<string>())
);
private void fileSavePerms_Click(object sender, RoutedEventArgs e)
{
// You create a new instance of List<string>
var newPermissionList = new List<string>();
// your foreach statement that fills this newPermissionList
// ...
// At the end you simply replace the property value with this new list
PermissionList = newPermissionList;
}
}
In the XAML file you will have this:
<ListBox
ItemsSource="{Binding PermissionList}"
HorizontalAlignment="Left"
VerticalAlignment="Top"
Margin="28,512,0,0"
Height="36"
Width="442"/>
Of course this solution can be improved.
You may use System.Collections.ObjectModel.ObservableCollection<string> type so that you no longer have to create a new instance of List<string> every time but you can clear the list and add the new items in your foreach statement.
You may use a ViewModel class (e.g. MainViewModel) that has this permission list and also implements the INotifyPropertyChanged interface and then you set an instance of this class to your WPF window's DataContext property.

WPF ComboBox Bound List set on DropDownOpened Event

My problem is that the ComboBox is not displaying the value stored in its bound list.
Here is what I'm doing:
WPF:
<ComboBox ItemsSource="{Binding Devices}"
DropDownOpened="deviceSelector_DropDownOpened"/>
Note that my Window's DataContext is {Binding RelativeSource={RelativeSource Self}}.
C# code-behind:
public List<String> Devices { get; set; }
private void deviceSelector_DropDownOpened(object sender, EventArgs e)
{
// the actual population of the list is occuring in another method
// as a result of a database query. I've confirmed that this query is
// working properly and Devices is being populated.
var dev = new List<String>();
dev.Add("Device 1");
dev.Add("Device 2");
Devices = dev;
}
I have tried doing this with an ObservableCollection instead of a List, and I've also tried using a PropertyChangedEventHandler. Neither of these approaches have worked for me.
Any idea why my items aren't being displayed when I click the dropdown?

Since you're doing this in code behind anyway, why not set the ComboBox.ItemsSource directly.
Now, I am not going to say this is the way it should be done in WPF (I would prefer the view's data to be loaded in a ViewModel), but it will solve your issue.
The reason why this isn't working is because your property doesn't inform the binding system when it changes. I know you said you tried it with PropertyChangedEventHandler, but that won't work unless your View looks like this:
public class MyView : UserControl, INotifyPropertyChanged
{
private List<String> devices;
public event PropertyChangedEventHandler PropertyChanged;
public List<String> Devices
{
get { return devices; }
set
{
devices = value;
// add appropriate event raising pattern
if (PropertyChanged != null)
PropertyChanged(this, new PropertyChangedEventArgs("Devices"));
}
}
...
}
Likewise, using an ObservableCollection would only work like this:
private readonly ObservableCollection<string> devices = new ObservableCollection<string>();
public IEnumerable<string> Devices { get { return devices; } }
private void deviceSelector_DropDownOpened(object sender, EventArgs e)
{
devices.Clear();
devices.Add("Device 1");
devices.Add("Device 2");
}
Either method should populate the ComboBox, and in a quick test I just ran, it worked.
Edit to add DependencyProperty method
One last way you can do this is with a DependencyProperty (as your View is a DependencyObject:
public class MyView : UserControl
{
public static readonly DependencyProperty DevicesProperty = DependencyProperty.Register(
"Devices",
typeof(List<string>),
typeof(MainWindow),
new FrameworkPropertyMetadata(null));
public List<string> Devices
{
get { return (List<string>)GetValue(DevicesProperty); }
set { SetValue(DevicesProperty, value); }
}
...
}

The following change (suggested by Abe Heidebrecht) fixed the problem, but I don't know why. Anyone willing to lend an explanation?
WPF:
<ComboBox DropDownOpened="deviceSelector_DropDownOpened"
Name="deviceSelector"/>
C# code-behind:
private void deviceSelector_DropDownOpened(object sender, EventArgs e)
{
var dev = new List<String>();
dev.Add("Device 1");
dev.Add("Device 2");
deviceSelector.ItemsSource = dev;
}

Unless I'm missing something here:
Try firing OnPropertyChanged when devices gets updated for the devices property, this should fix this. I have occasionally also had to set the mode:
ItemsSource="{Binding Devices, Mode=TwoWay}"
On some controls.
Setting the itemssource on the control directly tells the control to use new items directly, without using the binding hooked up in the xaml. Updating the Devices property on the datacontext does not tell the combobox that the Devices property has changed so it won't update. The way to inform the combobox of the change is to fire OnPropertyChanged for the devices property when it gets changed.