Develop Reference

Event handler can't be found in MVVM

I have a silverlight application. One of StackPanel will display the table. The first column is a check box.
<telerik:RadGridView.Columns>
<telerik:GridViewColumn Width="80" Header="Complete" HeaderTextAlignment="Center" TextAlignment="Center">
<telerik:GridViewColumn.CellTemplate>
<DataTemplate>
<CheckBox HorizontalAlignment="Center" IsChecked="{Binding Something, Converter={StaticResource ShortToBooleanConverter}}" Checked="Complete_Checked"></CheckBox>
</DataTemplate>
</telerik:GridViewColumn.CellTemplate>
</telerik:GridViewColumn>
What I want is that once I click the box, a message box with Y/N pops up. I do have a Complete_Checked method in MVVM. But I get the error
Event handler 'Complete_Checked` not found on class.....

You can't use click event handlers with MVVM you need to use CommandBinding or DataBinding depending on what you're doing.
With your example you'll use data binding. You want to bind to the checkbox dependency property called IsChecked. You'll also want to use the Mode of TwoWay. This will allow the UI to update the bound property when it changes.
<CheckBox IsChecked="{Binding CheckBoxIsChecked, Mode=TwoWay}">
Then in your object model not viewmodel
private bool _checkBoxIsChecked;
public bool CheckBoxIsChecked
{
get{ return _checkBoxIsChecked;}
set{_checkBoxIsChecked = value; OnPropertyChanged("CheckBoxIsChecked"); }
}

How to bind different properties to SelectedItem and SelectedIValue of ComboBox?

I have a thread that updates the current Mode property every second. I also want an option to be able to set a mode within the same cell in datagrid. So, in not editing mode I just show the mode. In editing mode, I show a populated ComboBox.
Now,
to be able to show the selected item in ComboBox, when I enter the editing mode, I bind the SelectedItem to Mode.
to be able to get the changes back to the ViewModel I bind SelectedValue to a different property. ( I need to bind to a different property since 'Mode' is updated every second and will overwrite the selected value).
The problem is that though SelectedItem is bound with Mode=OneTime it still triggers SelectedValue property. I want the SelectedValue to be triggered only when user select a value.
I hope it's clear what I'm trying to do. So, how I can achieve this? Other approaches are welcome (even if I need to use a different control).
<DataGridTemplateColumn Header="Mode">
<DataGridTemplateColumn.CellTemplate>
<DataTemplate>
<TextBlock Text="{Binding Mode}"/>
</DataTemplate>
</DataGridTemplateColumn.CellTemplate>
<DataGridTemplateColumn.CellEditingTemplate>
<DataTemplate>
<ComboBox ItemsSource="{Binding Source={StaticResource Modes}}"
SelectedItem="{Binding Mode, Mode=OneTime}"
SelectedValue="{Binding ModeToSet, Mode=OneWayToSource}"
/>
</DataTemplate>
</DataGridTemplateColumn.CellEditingTemplate>
</DataGridTemplateColumn>

The premise of what needs to be done is not attainable due to the way the combobox works and how Mode is constantly changing in the background.
Why?
The problem is that though SelectedItem is bound with Mode=OneTime it
still triggers SelectedValue property.
As it should. OneTime as per the docs (BindingMode Enumeration) states:
"Updates the binding target when the application starts or when the data context changes."
The data context as per your design is always changing once a second. If one reads farther into the description it states
"This type of binding is appropriate if you are using data where either a snapshot of the current state is appropriate to use or the data is truly static. ... This is essentially a simpler form of OneWay binding..."
And if one reads up on OneWay bindings
"Updates the binding target (target) property when the binding source (source) changes. This type of binding is appropriate if the control being bound is implicitly read-only."
A combo box is ultimately designed to change both SelectedItem and to get the value off of SelectedItem into SelectedValue
I want the SelectedValue to be triggered only when user select a value.
The problem is not going out of the control, it is what is coming in....
Create a test project and the combobox behaves the way you specify, selected value is only triggered when a user selects a value. Comboboxes only sets the SelectedX properties when a choice is made or an outside value has changed one so it changes the other.
Since Mode is constantly changing it is pushing the change into the selection, not visa versa.
Suggestion To Fix
I suggest you take a snapshot of mode and place that into a ModeOnEdit variable and bind that. When the user makes the selection, capture the event and change the actual Mode.
Test Project
Bind to your own data source, mine was Ships. Ships is a list with and Name as a property on that object. ToString on the ship object returns Name.
Here is the result, there are two textboxes which show the state of the selected item/value. A button to set the selected value and the combobox itself.
<Label Grid.Row="1" Grid.Column="1">SelectedItem</Label>
<TextBlock Grid.Row="1" Grid.Column="2" Text="{Binding SelectedItem, ElementName=cbMain}"/>
<Label Grid.Row="3" Grid.Column="1" Grid.ColumnSpan="2">SelectedValue</Label>
<TextBlock Grid.Row="3" Grid.Column="2" Text="{Binding SelectedValue, ElementName=cbMain}"/>
<Button Grid.Row="5" Grid.Column="1" Click="ChangeSelectedValue">Set Selected Value</Button>
<ComboBox Name="cbMain"
Grid.Row="5"
Grid.Column="2"
ItemsSource="{Binding Ships}"
SelectedValuePath="Name"/>
-- Code behind
private void ChangeSelectedValue(object sender, RoutedEventArgs e)
{
cbMain.SelectedValue = "Pacific Silver";
}

ComboBox selection in DataGrid gets reset when clicking on another column

I have a DataGrid with two Columns. One is a DataGridTextColumn the other is a DataGridComboBoxColumn. Both are bound to property and are editable. So when I change the selection of the ComboBox and then click at some white space the cell shows the correct selection. But if I click at the TextColumn beside it the ComboBox exits editing mode and resets the selection to whatever was selected before.
Why is this happening and what can I do to prevent this from happening?

Since you haven't posted your code I'm making assumptions as to what your problem is.
You need to specify TwoWay mode in your DataGrid.
You need to Bind the property SelectedValueBinding in your DataGridComboBoxColumn
<DataGridComboBoxColumn x:Name="DropDownComboBox" SelectedValueBinding="{Binding Path=FieldFromData}" Header="SomeName" IsReadOnly="False"/>
In the code define the combobox contents.
DropDownComboBox.ItemsSource = Enum.GetValues(typeof(ValuesPossible));
If you don't have the Binding set to the property in the data set you are displaying, it will just be a drop down that doesn't change the value of the data anywhere. The above example takes and populates the combobox with the values that could be selected and selects what is contained in the data set for the FieldFromData.
You will also need to bind the DataGrid in two way mode to allow the selected value to change the field.
<DataGrid ..<properties>.. ItemsSource="{Binding DataCollection,Mode=TwoWay}" />

<DataGridTemplateColumn Visibility="Visible" Header="Reason Id" Width="250">
<DataGridTemplateColumn.CellTemplate>
<DataTemplate>
<StackPanel>
<ComboBox x:Name="" SelectedValue="{Binding TypeId}" SelectedValuePath="TypeId" DisplayMemberPath="Type"
ItemsSource="{Binding TypeItems}" ></ComboBox>
</StackPanel>
</DataTemplate>
</DataGridTemplateColumn.CellTemplate>
</DataGridTemplateColumn>

Check your columns DataPropertyName property.
I had a similar issue. The 'Type' was never getting set. Code was getting set twice, but incorrectly on the 2nd time.
Incorrect:
grcLocMill2Code.DataPropertyName = "MillCodeId";
grcLocMill2Code.DataPropertyName = "MillTypeId";
Correct:
grcLocMill2Code.DataPropertyName = "MillCodeId";
grcLocMill2Type.DataPropertyName = "MillTypeId";

Name checkboxes in ListView

I have a ListView control that contains one column with checkboxes only. Is it possible to give those checkboxes some names (indexes - like 1, 2, 3...)?
I need it because I want to identify a concrete checkbox in ToggleButton_OnCheckedUnchecked event in some way.
<GridViewColumn.CellTemplate>
<DataTemplate>
<CheckBox IsChecked="{Binding Value, Mode=OneWay}" IsThreeState="False"
Checked="ToggleButton_OnCheckedUnchecked"
Unchecked="ToggleButton_OnCheckedUnchecked"/>
</DataTemplate>
</GridViewColumn.CellTemplate>

Don't do it that way. Instead, have each line in your ListView have an IsChecked property, and change the IsChecked Binding to TwoWay. That way, you don't need to use the Checked and UnChecked events at all.
public class LineViewModel
{
public bool IsChecked
{
get { return _isChecked;
}
set
{
// do something here
}
}
<GridViewColumn.CellTemplate>
<DataTemplate>
<CheckBox IsChecked="{Binding IsChecked, Mode=TwoWay}" IsThreeState="False"/>
</DataTemplate>
</GridViewColumn.CellTemplate>
For best results, implement INotifyPropertyChanged too.

Probably dynamic binding some names can be done through the Binding, like that:
<CheckBox Name="{Binding IdCheckBox}" ... />
Quote from the MSDN:
Data binding a Name is technically possible, but is an extremely uncommon scenario because a data-bound Name cannot serve the main intended purpose of the property: to provide an identifier connection point for code-behind.
In short, the Binding Name property for control is impossible and undesirable. But you can use the attached dependency property, like this:
<CheckBox local:GiveName.Name="{Binding Template_Name1}" ... />
In any case, this is not the solution to your problems.

Getting Checked property from CheckBox when Command is called in WPF

I have a grid of CheckBoxes in a WPF C# project. Each CheckBox's Command property is bound to a CheckBoxChangedCommand in my WView.xaml file, like so:
<CheckBox Grid.Row="0" IsChecked="true" x:Name ="CheckBox0"
Command="{Binding CheckBoxChangedCommand}" />
<CheckBox Grid.Row="1" IsChecked="true" x:Name="CheckBox1"
Command="{Binding CheckBoxChangedCommand}" />
Each time one of the CheckBoxes is either checked or unchecked, I call CheckBoxChanged. How would I go about displaying a pop-up window showing either 1. the row number in the grid of the CheckBox and the name of the CheckBox ("CheckBox0", for example) and 2. The Checked value (true/false) for the checkbox?
My CheckBoxChangedCommand, in WViewModel.cs file, looks like this:
public ICommand CheckBoxChangedCommand
{
get
{
return new RelayCommand(param =>
{
MessageBox.Show("CheckBoxChanged!");
});
}
}
How can I access the IsChecked property and the row number of the CheckBox that triggered CheckBoxChanged from withinCheckBoxChanged? How can I pass the data from my View to my ViewModel?

You definitely need to do more with binding here.
First of all, you should probably be binding the IsChecked property of your Checkboxes to a property on your viewmodel.
Second, based on your comment about needing to know the row number of the checkbox that was checked, I'd say you probably need to be generating the "row" including the CheckBox via databinding, so that you can then pass the object that represents the row as the CommandParameter to your CheckBoxChangedCommand.
So something like:
<ListBox ItemsSource="{Binding MyItems}" />
and then in your resources:
<DataTemplate DataType="{x:Type local:MyItemType}">
<CheckBox IsChecked="{Binding IsChecked}"
Command="{Binding CheckChangedCommand}"
CommandParameter="{Binding}" />
</DataTemplate>
Note: Your CheckChangedCommand is probably on the main ViewModel, not the item-level ViewModel, so you probably need to do some other type of lookup to make it find it - this example is just for simplicity