I have a MVVM run treeview. On the top level is an Account object that contains credentials. I have a PasswordBox that can be used to change the account password with a Save button right behind it. The code is as follows and is part of the Account level template:
PasswordBox Width="100" x:Name="pbPassword"/>
Button x:Name="btnSave" Command="{Binding ClickCommand}" CommandParameter="{Binding ElementName=pbPassword, Path=Password}" Height="20" Width="50">Save
I put something into the PasswordBox and then click Save. The ClickCommand fires, but the parameter is always string.Empty. What am I missing?
For security reasons, WPF doesn't provide a dependency property for the Password property of PasswordBox (reference 1, 2), so your command parameter binding doesn't work.
You could bind the command argument to PasswordBox, then access the appropriate property from within your command implementation:
<Button Command="{Binding ClickCommand}" CommandParameter="{Binding ElementName=pbPassword}">
// command implementation
public void Execute(object parameter)
{
var passwordBox = (PasswordBox)parameter;
var value = passwordBox.Password;
}
You may want to consider other options that do not involve keeping the password in memory as plain text.
Hope this helps,
Ben
--PLEASE STOP MARKING ME DOWN ON THIS, See comment below, this does not work, but left in so no-one else makes the same mistake--
Sorry old Q, but found an improvement on that
<Button Content="Log On"
Command="{Binding LogOnCommand}"
CommandParameter="{Binding ElementName=PasswordControl, Path=SecurePassword}" />
that way your command need only know about a SecureString object
public override void Execute(object parameter)
{
_viewModel.LogOnAsync((SecureString)parameter);
}
keeping knowledge of the ui from the command
Related
I have read some thread about how to work on WPF ListView command binding.
Passing a parameter using RelayCommand defined in the ViewModel
Binding Button click to a method
Button Command in WPF MVVM Model
How to bind buttons in ListView DataTemplate to Commands in ViewModel?
All of them suggest write the logic code inside ViewModel class, for example:
public RelayCommand ACommandWithAParameter
{
get
{
if (_aCommandWithAParameter == null)
{
_aCommandWithAParameter = new RelayCommand(
param => this.CommandWithAParameter("Apple")
);
}
return _aCommandWithAParameter;
}
}
public void CommandWithAParameter(String aParameter)
{
String theParameter = aParameter;
}
It is good practice or anyway so I can move the CommandWithAParameter() out of the ViewModel?
In principle, MVVM application should be able to run to its full potential without creating the views. That's impossible, if some parts of your logic are in View classes.
On top of that, ICommand has CanExecute, which will autamagically disable buttons, menu items etc. if the command should not be run.
I understand why with basic RelayCommand implementation it can be hard to see the benefits, but take a look at ReactiveCommand samples.
ReactiveCommand handles async work very well, even disabling the button for the time work is done and enabling it afterwards.
Short example: you have a login form. You want to disable the login button if the username and password are empty.
Using commands, you just set CanExecute to false and it's done.
Using events, you have manualy disable/enable the button, remember that it has to be done in Dispatcher thread and so on - it gets very messy if you have 5 buttons depending on different properties.
As for ListView, commands are also usefull - you can bind current item as command parameter:
<ListView ItemsSource="{Binding MyObjects}">
<ListView.ItemTemplate>
<DataTemplate>
<DockPanel>
<!-- change the context to parent ViewModel and pass current element to the command -->
<Button DockPanel.Dock="Right" Command="{Binding ElementName=Root, Path=ViewModel.Delete}" CommandParameter="{Binding}">Delete</Button>
<TextBlock Text="{Binding Name}"/>
</DockPanel>
</DataTemplate>
</ListView.ItemTemplate>
</ListView>
I have a button which should be used as Connect or Disconnect button, depending on the Connected-property of the ViewModel:
<Button Content="_Connect" x:Name="connectButton" Command="{Binding ConnectCommand}"/>
Now depending on the property, the content should be either "_Connect" or "_Disconnect" and the command binding should go either to ConnectCommand or DisconnectCommand.
Is there a nice way of doing that or should I use a command for both and have a DataTrigger to set the content separately depending on the Connected property?
Thanks a lot!
Using same command you can handle this with enum.
<Button Name="btnOption"
Grid.Row="0"
Grid.RowSpan="3"
Grid.Column="8"
Command="{Binding RxOptionCommand}"
Content="{Binding RxOptionContent}" />
Based on your View Model's connect or disconnect business change the button content and at the same time set your enum value in to a variable.
public enum EnumRxRecStatus
{
None = 0,
New = 1,
}
Now you can check the condition in to your command event
public void OnRxOptionCommand(object sender)
{
if (RequestForRxOption == EnumRxRecStatus.None)
{
// Do something
}
else if (RequestForRxOption == EnumRxRecStatus.New)
{
// Do something
}
}
It is indeed very simple:
As Clemens suggested, I ended up setting the Binding and the Contents with a DataTrigger.
I have the following code which uses Microsoft's WPFToolkit AutoCompleteBox. I have tried adding an input binding inside it
xmlns:tk="clr-namespace:System.Windows.Controls;assembly=System.Windows.Controls.Input.Toolkit"
<tk:AutoCompleteBox IsTextCompletionEnabled="True" FilterMode="Contains" ItemsSource="{Binding DistinctItemNames, Mode=OneWay}"
SelectedItem="{Binding SelectedItemName, Mode=TwoWay, UpdateSourceTrigger=PropertyChanged}"
x:Name="searchBox" Width="300" Height="23" VerticalContentAlignment="Center" >
<tk:AutoCompleteBox.InputBindings>
<KeyBinding Key="Return" Command="{Binding ShowSelectedItemsCommand}"/>
<tk:AutoCompleteBox.InputBindings>
</tk:AutoCompleteBox>
However, it doesn't work. I expect that the control itself handles the 'Enter' or 'Return' key so how can I override its default function?
I have also put that keybinding directly under the 'UserControl.InputBindings' and it also did not work. I hate to use Code Behind to handle the command logic.
You could try to handle the PreviewKeyDown event, either directly in the code-behind of the view:
private void AutoCompleteBox_PreviewKeyDown(object sender, KeyEventArgs e)
{
if (e.Key == Key.Enter)
{
AutoCompleteBox box = sender as AutoCompleteBox;
dynamic viewModel = box.DataContext;
viewModel.ShowSelectedItemsCommand.Execute(null);
}
}
...or by wrapping it in an attached behaviour: https://www.codeproject.com/Articles/28959/Introduction-to-Attached-Behaviors-in-WPF.
Neither approach breaks the MVVM pattern. In the first case you are just invoking the exact same view model command from the exact same view. But if you really "hate to use code-behind" for some strange reason, then create an attached behaviour.
Try having a look at this post: ReactiveCommand pass Command Parameter.
It uses Reactivity to accomplish the same thing you want.
Then, you can process the key received via KeyCode, and check if it is the key you want.
I am trying to figure out the best way to select all the text in a TextBox the first time the control is loaded. I am using the MVVM pattern, so I am using two-way binding for the Text property of the TextBox to a string on my ViewModel. I am using this TextBox to "rename" something that already has a name, so I would like to select the old name when the control loads so it can easily be deleted and renamed. The initial text (old name) is populated by setting it in my ViewModel, and it is then reflected in the TextBox after the data binding completes.
What I would really like to do is something like this:
<TextBox x:Name="NameTextBox" Text="{Binding NameViewModelProperty, Mode=TwoWay}" SelectedText="{Binding NameViewModelProperty, Mode=OneTime}" />
Basically just use the entire text as the SelectedText with OneTime binding. However, that does not work since the SelectedText is not a DependencyProperty.
I am not completely against adding the selection code in the code-behind of my view, but my problem in that case is determining when the initial text binding has completed. The TextBox always starts empty, so it can not be done in the constructor. The TextChanged event only seems to fire when a user enters new text, not when the text is changed from the initial binding of the ViewModel.
Any ideas are greatly appreciated!
Dan,
I wrote a very simple derived class, TextBoxEx, that offers this functionality. The TextBoxEx class derives from TextBox, and can be referenced in XAML for any and all of your TextBox’s. There are no methods to call. It just listens for Focus events and selects it own text. Very simple.
Usage is as follows:
In XAML, reference the assembly where you implement the TextBoxEx class listed below, and add as many TextBoxEx elements as you need. The example below uses data binding to display a username.
<UserControl x:Class="MyApp.MainPage"
xmlns="http://schemas.microsoft.com/client/2007"
xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
xmlns:c="clr-namespace:ClassLibrary;assembly=ClassLibrary"
>
.
.
.
<c:TextBoxEx x:Name="NameTextBox" Text="{Binding NameViewModelProperty, Mode=TwoWay}" Width="120" />
This code below works with Silverlight 3.
using System.Windows;
using System.Windows.Controls;
namespace ClassLibrary
{
// This TextBox derived class selects all text when it receives focus
public class TextBoxEx : TextBox
{
public TextBoxEx()
{
base.GotFocus += OnGotFocus;
}
private void OnGotFocus(object sender, RoutedEventArgs e)
{
base.SelectAll();
}
}
}
Good luck.
I'm leaving Jim's solution as the answer, since calling SelectAll() on the GotFocus event of the TextBox did the trick.
I actually ended up making a Blend TriggerAction and an EventTrigger to do this instead of subclassing the TextBox or doing it in code-behind. It was really simple to do and nice to be able to keep the behavior logic encapsulated and just add it declaratively in XAML to an existing TextBox.
Just posting this in case anyone else comes across this thread and is interested:
XAML:
<TextBox x:Name="NameTextBox" Text="{Binding NameViewModelProperty, Mode=TwoWay}">
<i:Interaction.Triggers>
<i:EventTrigger EventName="GotFocus">
<local:SelectAllAction/>
</i:EventTrigger>
</i:Interaction.Triggers>
</TextBox>
C#
public class SelectAllAction : TriggerAction<TextBox>
{
protected override void Invoke(object parameter)
{
if (this.AssociatedObject != null)
{
this.AssociatedObject.SelectAll();
}
}
}
Just wanna add a link I found pertaining to this - here is a fantastic discussion (read comments) on Behaviours vs subclassing vvs attached properties...
This is MVVM application. There is a window and related view model class.
There is TextBox, Button and ListBox on form. Button is bound to DelegateCommand that has CanExecute function. Idea is that user enters some data in text box, presses button and data is appended to list box.
I would like to enable command (and button) when user enters correct data in TextBox. Things work like this now:
CanExecute() method contains code that checks if data in property bound to text box is correct.
Text box is bound to property in view model
UpdateSourceTrigger is set to PropertyChanged and property in view model is updated after each key user presses.
Problem is that CanExecute() does not fire when user enters data in text box. It doesn't fire even when text box lose focus.
How could I make this work?
Edit:
Re Yanko's comment:
Delegate command is implemented in MVVM toolkit template and when you create new MVVM project, there is Delegate command in solution. As much as I saw in Prism videos this should be the same class (or at least very similar).
Here is XAML snippet:
...
<UserControl.Resources>
<views:CommandReference x:Key="AddObjectCommandReference"
Command="{Binding AddObjectCommand}" />
</UserControl.Resources>
...
<TextBox Text="{Binding ObjectName, UpdateSourceTrigger=PropertyChanged}"> </TextBox>
<Button Command="{StaticResource AddObjectCommandReference}">Add</Button>
...
View model:
// Property bound to textbox
public string ObjectName
{
get { return objectName; }
set {
objectName = value;
OnPropertyChanged("ObjectName");
}
}
// Command bound to button
public ICommand AddObjectCommand
{
get
{
if (addObjectCommand == null)
{
addObjectCommand = new DelegateCommand(AddObject, CanAddObject);
}
return addObjectCommand;
}
}
private void AddObject()
{
if (ObjectName == null || ObjectName.Length == 0)
return;
objectNames.AddSourceFile(ObjectName);
OnPropertyChanged("ObjectNames"); // refresh listbox
}
private bool CanAddObject()
{
return ObjectName != null && ObjectName.Length > 0;
}
As I wrote in the first part of question, following things work:
property setter for ObjectName is triggered on every keypress in textbox
if I put return true; in CanAddObject(), command is active (button to)
It looks to me that binding is correct.
Thing that I don't know is how to make CanExecute() fire in setter of ObjectName property from above code.
Re Ben's and Abe's answers:
CanExecuteChanged() is event handler and compiler complains:
The event
'System.Windows.Input.ICommand.CanExecuteChanged'
can only appear on the left hand side
of += or -=
there are only two more members of ICommand: Execute() and CanExecute()
Do you have some example that shows how can I make command call CanExecute().
I found command manager helper class in DelegateCommand.cs and I'll look into it, maybe there is some mechanism that could help.
Anyway, idea that in order to activate command based on user input, one needs to "nudge" command object in property setter code looks clumsy. It will introduce dependencies and one of big points of MVVM is reducing them.
Edit 2:
I tried to activate CanExecute by calling addObjectCommand.RaiseCanExecuteChanged() to ObjectName property setter from above code. This does not help either. CanExecute() is fired few times when form is initialized, but after that it never gets executed again. This is the code:
// Property bound to textbox
public string ObjectName
{
get { return objectName; }
set {
objectName = value;
addObjectCommand.RaiseCanExecuteChanged();
OnPropertyChanged("ObjectName");
}
}
Edit 3: Solution
As Yanko Yankov and JerKimball wrote, problem is static resource. When I changed button binding like Yanko suggested:
<Button Command="{Binding AddObjectCommand}">Add</Button>
things started to work immediately. I don't even need RaiseCanExecuteChanged(). Now CanExecute fires automatically.
Why did I use static resource in first place?
Original code was from WPF MVVM toolkit manual. Example in that manual defines commands as static resource and then binds it to menu item. Difference is that instead of string property in my example, MVVM manual works with ObservableCollection.
Edit 4: Final explanation
I finally got it. All I needed to do was to read comment in CommandReference class. It says:
/// <summary>
/// This class facilitates associating a key binding in XAML markup to a command
/// defined in a View Model by exposing a Command dependency property.
/// The class derives from Freezable to work around a limitation in WPF when
/// databinding from XAML.
/// </summary>
So, CommandReference is used for KeyBinding, it is not for binding in visual elements. In above code, command references defined in resources would work for KeyBinding, which I don't have on this user control.
Of course, sample code that came with WPF MVVM toolkit were correct, but I misread it and used CommandReference in visual elements binding.
This WPF MVVM really is tricky sometimes.
Things look much clearer now with the edits, thanks! This might be a stupid question (I'm somewhat tired of a long day's work), but why don't you bind to the command directly, instead of through a static resource?
<Button Command="{Binding AddObjectCommand}">Add</Button>
Since you are using the DelegateCommand, you can call it's RaiseCanExecuteChanged method when your text property changes. I'm not sure what you are trying to accomplish with your CommandReference resource, but typically you just bind the commands directly to the button element's Command property:
<TextBox Text="{Binding ObjectName, UpdateSourceTrigger=ValueChanged}" />
<Button Command="{Binding AddObjectCommand}" Content="Add" />
This would be the relevant portion of your view model:
public string ObjectName
{
get { return objectName; }
set
{
if (value == objectName) return;
value = objectName;
AddObjectCommand.RaiseCanExecuteChanged();
OnPropertyChanged("ObjectName");
}
}
Try raising CanExecuteChanged when your property changes. The command binding is really distinct from the property binding and buttons bound to commands are alerted to a change in status by the CanExecuteChanged event.
In your case, you could fire a check when you do the PropertyChanged on the bound property that would evaluate it and set the command's internal CanExecute flag and then raise CanExecuteChanged. More of a "push" into the ICommand object than a "pull".
Echoing Abe here, but the "right" path to take here is using:
public void RaiseCanExecuteChanged();
exposed on DelegateCommand. As far as dependencies go, I don't think you're really doing anything "bad" by raising this when the property that the command depends on changes within the ViewModel. In that case, the coupling is more or less contained wholly within the ViewModel.
So, taking your above example, in your setter for "ObjectName", you would call RaiseCanExecuteChanged on the command "AddObjectCommand".
I know this is an old question but I personally think it's easier to bind the textbox Length to button's IsEnabled property, e.g.:
<TextBox Name="txtbox" Width="100" Height="30"/>
<Button Content="SomeButton " Width="100" Height="30"
IsEnabled="{Binding ElementName=txtbox, Path=Text.Length, Mode=OneWay}"></Button>
If ElementName binding does not work, use:
<Entry x:Name="Number1" Text="{Binding Number1Text}" Keyboard="Numeric"></Entry>
<Entry x:Name="Number2" Text="{Binding Number2Text}" Keyboard="Numeric"></Entry>
<Button Text="Calculate" x:Name="btnCalculate" Command="{Binding CalculateCommand}" IsEnabled="{Binding Source={x:Reference Number1, Number2}, Path=Text.Length, Mode=OneWay}"></Button>
or use:
<Entry x:Name="Number1" Text="{Binding Number1Text}" Placeholder="Number 1" Keyboard="Numeric"></Entry>
<Entry x:Name="Number2" Text="{Binding Number2Text}" Placeholder="Number 2" Keyboard="Numeric"></Entry>
<Button VerticalOptions="Center" Text="Calculate" x:Name="btnCalculate" Command="{Binding CalculateCommand}">
<Button.Triggers>
<DataTrigger TargetType="Button"
Binding="{Binding Source={x:Reference Number1, Number2},
Path=Text.Length}"
Value="{x:Null}">
<Setter Property="IsEnabled" Value="False" />
</DataTrigger>
</Button.Triggers>