Invoking command on TextChange is not updating Text Source Immediately - mvvm-light

Question

I am using MVVM light in my windows phone 8.1 here is code
xaml
<TextBox Text="{Binding SearchText, Mode=TwoWay,UpdateSourceTrigger=PropertyChanged}" >
<Interactivity:Interaction.Behaviors>
<Core:EventTriggerBehavior EventName="TextChanged">
<Core:InvokeCommandAction Command="{Binding SearchTextChanged}"></Core:InvokeCommandAction>
</Core:EventTriggerBehavior>
</Interactivity:Interaction.Behaviors>
</TextBox>
here is my VM
private RelayCommand _searchTextChanged;
/// <summary>
/// Gets the SearchTextChanged.
/// </summary>
public RelayCommand SearchTextChanged
{
get
{
return _searchTextChanged
?? (_searchTextChanged = new RelayCommand(
() =>
{
LoadContents(this.SearchText);
}));
}
}
each time text is changed SearchTextChanged command is firing properly but the text in SearchText property is not updated it is one character less. e.g. if text in textbox is A than SearchText contains null. If text in textbox is 'aaa' than text in SearchText is only 'aa' the last character is always missing.
Any Ideas?

Answer 1

OK, so based on the comments, here's the answer - don't use the InvokeCommandAction but the two-way binding.
<TextBox Text="{Binding SearchText, Mode=TwoWay,UpdateSourceTrigger=PropertyChanged}" />
In the viewmodel behind this, there's a property called SearchText which has a setter that can call the LoadContents method, something like this...
public string SearchText
{
get { return this.searchText; }
set
{
this.searchText = value;
NotifyPropertyChanged("SearchText");
LoadContents(this.searchText);
}
}
Every time the string in the TextBox changes, the setter is invoked and so is the LoadContents method.

Answer 2

Bumped into a very similar situation but the given workaround wasn't a solution in my case! So discovered another way to update the value.
The solution:
Pass the element as parameter to the command and update the source and then call the method.
public string SearchText
{
get { return this.searchText; }
set
{
this.searchText = value;
NotifyPropertyChanged("SearchText");
}
}
public RelayCommand SearchTextChanged
{
get
{
return _searchTextChanged
?? (_searchTextChanged = new RelayCommand(
() =>
{
someCommandAction();
}));
}
}
private void someCommandAction(object obj)
{
TextBox textBox = (obj as TextBox);
if (textBox != null)
{
var be = textBox.GetBindingExpression(TextBox.TextProperty);
if (be != null)
be.UpdateSource();
}
LoadContents(textBox.Text); //textBox.text or the SearchTextproperty itself
}
XAML part:
<TextBox x:Name="textBoxName" Text="{Binding SearchText,Mode=TwoWay,UpdateSourceTrigger=PropertyChanged}" >
<Interactivity:Interaction.Behaviors>
<Core:EventTriggerBehavior EventName="TextChanged">
<Core:InvokeCommandAction Command="{Binding SearchTextChanged}"
CommandParameter="{Binding ElementName=textBoxName}" />
</Core:EventTriggerBehavior>
</Interactivity:Interaction.Behaviors>
</TextBox>