I have a class which has implemented INotifyPropertyChanged. This class UserInfo has a boolean variable isuserLoggedIn.
Now in my mainform I have buttons whose isEnabled I wish to bind to UserInfo.isuserLoggedIn.
How to do that?
public class UserInfo : INotifyPropertyChanged
{
private static readonly UserInfo _instance = new UserInfo();
private string username;
private bool isLoggedIn;
public string UserName
{
get { return username; }
set
{
username = value;
NotifyPropertyChanged("UserName");
}
}
public bool UserLoggedIn
{
get { return isLoggedIn; }
set
{
isLoggedIn = value;
NotifyPropertyChanged("UserLoggedIn");
}
}
public event PropertyChangedEventHandler PropertyChanged;
public void NotifyPropertyChanged(string propertyName)
{
if (PropertyChanged != null)
{
PropertyChanged(this, new PropertyChangedEventArgs(propertyName));
}
}
public static UserInfo GetUserInfo()
{
return _instance;
}
}
In the main I have:
public class MainWindow
{
UserInfo currentUser = UserInfo.GetUserInfo();
}
The XAML is:
<Button IsEnabled="{Binding ElementName=currentUser, Path=UserLoggedIn}"/>
You'll need to set the DataContext of your view to an instance of your UserInfo class. And then bind the IsEnabled property of your button to the UserIsLoggedIn boolean property on your UserInfo view model. Here's an example of binding an element's attribute to a property on a corresponding view model: passing a gridview selected item value to a different ViewModel of different Usercontrol
After seeing your edit, you'll again need to set the DataContext of your view to the currentUser object, then remove the ElementName portion of your button's IsEnabled binding expression.
You can bind IsEnabled to Length of the username textbox:
<TextBox Name="usernameTxt" Width="100" Height="30"/>
<Button Content="SomeButton " Width="100" Height="30"
IsEnabled="{Binding ElementName=usernameTxt, Path=Text.Length, Mode=OneWay}"></Button>
Related
I am struggling with this for a while and I cannot figure it out. I have a button and a textBox. The textBox is linked to a property named: MessageDisplay. I want to be able to access this property and update the textBox in several places. Sadly, the PropertyChanged is null. The weird thing is that if I copy/paste the MessageDisplayModel class into the *MessageViewModel * class, it works ...
here is my code :
XAMLfile :
<Grid>
<Button Command="{Binding DisplayTextCommand}" Name="DisplayTextCommand" Margin="53,72,544.6,286" Width="Auto">Push</Button>
<TextBox Name="MessageDisplay" Text="{Binding MessageDisplay, UpdateSourceTrigger=PropertyChanged, Mode=TwoWay}" />
</Grid>
MessageDisplayModel file
public class MessageDisplayModel : INotifyPropertyChanged
{
public event PropertyChangedEventHandler PropertyChanged;
private string _message;
public string MessageDisplay
{
get { return _message; }
set
{
this._message = value;
this.OnPropertyChanged("MessageDisplay");
}
}
public void UpdateTextBox(string output)
{
MessageDisplay = output;
}
protected virtual void OnPropertyChanged(string propertyName)
{
PropertyChangedEventHandler handler = this.PropertyChanged;
if (handler != null)
{
var e = new PropertyChangedEventArgs(propertyName);
handler(this, e);
}
}
}//class
MessageViewModel file:
public class MessageViewModel
{
private ICommand _testCommand;
public MessageDisplayModel MessageDisplaySmt = new MessageDisplayModel();
public ICommand DisplayTextCommand
{
get
{
return new DelegateCommand(DisplayMessage);
}
set
{
if (_testCommand == value) return;
_testCommand = value;
}
}
public void DisplayMessage()
{
MessageDisplaySmt.UpdateTextBox("Successfuly downloaded");
}
}//class
MainWindow file
public partial class MainWindow : Window
{
public MainWindow()
{
InitializeComponent();
MessageDisplay.DataContext = new MessageDisplayModel();
DisplayTextCommand.DataContext = new MessageViewModel();
}
}//class
I update the MessageDisplay property by using the method UpdateTextBox(string). I call this method on the click of the button. When debugging the property gets updated but when time comes to notify the UI that the property has changed, PropertyChangedEventHandler PropertyChanged has its value null ... But if I write something in the textBox, the PropertyChangedEventHandler PropertyChanged gets changed and isn't null anymore. All I want is to be able to change the textBox's property whenever I want and from anywhere I want to.
Thank you
You are using two different instances of MessageDisplayModel. You must use a shared instance.
Also the DisplayTextCommand is implemented "wrong". The set method is redundant as the property's get always returns a new instance of the ICommand.
MessageViewModel.cs
public class MessageViewModel
{
pulic MessageViewModel()
{
}
pulic MessageViewModel(MessageDisplayViewModel messageDisplayViewModel)
{
this.MessageDisplaySmt = messageDisplayViewModel;
}
public void DisplayMessage()
{
this.MessageDisplaySmt.UpdateTextBox("Successfuly downloaded");
}
public MessageDisplayViewModel MessageDisplaySmt { get; set; }
public ICommand DisplayTextCommand { get => new DelegateCommand(DisplayMessage); }
}
MainWindow.xaml.cs
public partial class MainWindow : Window
{
public MainWindow()
{
InitializeComponent();
// Alternatively use XAML to set the DataContext (see MainWindow.xaml). Would require a parameterless constructor.
this.DataContext = new MessageViewModel(new MessageDisplayViewModel());
}
}
MainWindow.xaml
<Window>
<!--
Alternative DataContext declaration using XAML instead of C#.
Requires a parameterless constructor for both view model objects.
-->
<Window.DataContext>
<MessageViewModel>
<MessageViewModel.MessageDisplaySmt>
<MessageDisplayViewModel />
</MessageViewModel.MessageDisplaySmt>
</MessageViewModel>
</Window.DataContext>
<StackPanel>
<Button Command="{Binding DisplayTextCommand}"
Content="Push" />
<TextBox Text="{Binding MessageDisplaySmt.MessageDisplay}" />
</StackPanel>
</Window>
I have next model:
public class MyModel
{
public ObservableCollection<MyObject> MyList {get; set;}
}
public class MyObject
{
MyObservableDictionary MyDictionary {get; set;}
}
public class MyObservableDictionary : ObservableCollection<EnymValue>
{
}
public class EnymValue : INotifyPropertyChanged
{
private MyEnum key;
private string value;
public MyEnum Key
{
get
{
return this.key;
}
set
{
this.key = value;
NotifyPropertyChanged("Key");
}
}
public string Value
{
get
{
return this.value;
}
set
{
this.value = value;
NotifyPropertyChanged("Value");
}
}
public LanguageValue(MyEnum key, string value)
{
this.Key = key;
this.Value = value;
}
public event PropertyChangedEventHandler PropertyChanged;
public void NotifyPropertyChanged([System.Runtime.CompilerServices.CallerMemberName]string propertyName = "")
{
if (PropertyChanged != null)
{
PropertyChanged(this, new PropertyChangedEventArgs(propertyName));
}
}
}
public enum MyEnum
{
}
And on View I have a ListBox:
<ListBox x:Name="MyList" SelectionMode="Single" ItemsSource="{Binding Path=MyList, Mode=OneWay}">
<ListBox.ItemTemplate>
<DataTemplate>
<TextBlock Text="{Binding Path=MyDictionary, Mode=OneWay, Converter={StaticResource myEnumToTextConverter}}" />
</DataTemplate>
</ListBox.ItemTemplate>
</ListBox>
(myEnumToTextConverter converter is just selects first element from collection and return it's value, or some specified constant if collection is null or empty)
I want my Model's list box to be updated on view, when any EnymValue values are changed.
Is it possible somehow to implement this?
Currently the view is not updated when Value changed.
I've tried to inherit EnymValue from INotifyPropertyChanged, but this didn't helped. Looks like PropertyChanged == null on EnymValue.NotifyPropertyChanged when property updated.
ObservableCollection is able to notify UI about changes when collection itself is changed(elemends are added or deleted). But ObservableCollection is not aware of changes that are happening when you modify one of it's items. To solve the problem you may subscribe to CollectionChange event of observable collection, and when new item is added, subscribe to new items's PropertyChanged. When PropertyChanged event is raised, you can trigger notification on your list OnPropertyChanged(()=>MyItems); You should be careful implementing this solution and remember to unsubscribe from the event's to avoid memory leaks.
An example of what I mean you can see in this answer.
Your MyDictionary should force a refresh. Easiest way is to re-assign its old value, and implement INPC in MyObject like below :
public class MyObject: INotifyPropertyChanged
{
MyObservableDictionary _myDictionary;
public MyObservableDictionary MyDictionary {
get
{
return _myDictionary;
}
set
{
_myDictionary = value;
OnPropertyChanged("MyDictionary");
}
}
public MyObject()
{
MyDictionary = new MyObservableDictionary();
}
public event PropertyChangedEventHandler PropertyChanged;
public void OnPropertyChanged(string prop)
{
if (PropertyChanged != null)
PropertyChanged(this, new PropertyChangedEventArgs(prop));
}
}
Sample code to change Value :
private void Button_Click(object sender, RoutedEventArgs e)
{
// vm is ViewModel instance, vm is DataContext set for Window
var old = vm.MyList[0].MyDictionary;
vm.MyList[0].MyDictionary[0].Value = "aaaa";
vm.MyList[0].MyDictionary = old;
}
I tested this, and it displays changed value as "aaaa".
I think I may be using the DependencyObject incorrectly.
I have a generic class that implements the DependencyObject called Person with the properties FirstName and LastName.
public class Person : DependencyObject
{
public static readonly DependencyProperty FirstNameProperty =
DependencyProperty.Register("FirstName", typeof(string), typeof(Person));
public string FirstName
{
get { return (string)GetValue(FirstNameProperty); }
set { SetValue(FirstNameProperty, value); }
}
public static readonly DependencyProperty LastNameProperty =
DependencyProperty.Register("LastName", typeof(string), typeof(Person));
public string LastName
{
get { return (string)GetValue(LastNameProperty); }
set { SetValue(LastNameProperty, value); }
}
}
Then I have a xaml control with its datacontext set to my ViewModel class. Inside the ViewModel class I have a property called UserName that gets/sets a Person. The text box is bound to the UserName.FirstName property. It can populate the textbox correctly but can't seem to call the set when I enter characters and tab out. I think the issue is the two level property binding. For design reasons I need to access it through two levels of properties. Any suggestions?
Here is my xaml:
<TextBox Width="100" Margin="10,0,0,0" Text="{Binding Path=UserName.FirstName, Mode=TwoWay}" />
Here is my property in the view model class:
public Person UserName
{
get
{
return person;
}
set
{
person = value;
}
}
I've also tried it this way too:
public Person UserName
{
get
{
return person;
}
set
{
person.FirstName = value.FirstName;
}
}
Your property will not be called from the binding, the property is only there because of the pattern so it is easily visible from code.
The binding sets the dependency property directly.
Why do you want dependency properties in this situation? Dependency properties are relevant on controls - for your scenario use regular properties and INotifyPropertyChanged - the code will be simpler that way :)
If you do want notification when a dependencyproperty is changed you have to add a static eventhandler to the DependencyProperty.Register(...) call.
Agree with rune Andersen.
You should use INotifyPropertyChanged.
public class Person :INotifyPropertyChanged
{
private string _firstName;
public string FirstName
{
get { return _firstName; }
set { _firstName = value; OnPropertyChanged("FirstName"); }
}
private string _lastName;
public string LastName
{
get { return _lastName; }
set { _lastName = value; OnPropertyChanged("LastName"); }
}
public event PropertyChangedEventHandler PropertyChanged;
protected void OnPropertyChanged(string name)
{
PropertyChangedEventHandler handler = PropertyChanged;
if (handler != null)
{
handler(this, new PropertyChangedEventArgs(name));
}
}
}
I am new to MVVM. to learn I created a sample application to show a message in a text box while clicking on button. In my code the button command is working properly but the property is not binding to the Textbox. How to bind Property to Textbox using MVVM?
My code is similar like given below.
View
<TextBox Name="MessageTextBox" Text="{Binding TestMessage}"/>
<Button Content="Show" Name="button1" Command="{Binding ShowCommand}">
<!-- Command Handler -->
</Button>
View Model
MyMessage myMessage;
public MainViewModel()
{
myMessage=new MyMessage();
}
//inside the ShowCommand Handler
TestMessage="Hello World";
// A Property to set TextBox Value.
Model
public class MyMessage: INotifyPropertyChanged
{
private string testMessage;
public string TestMessage
{
get { return testMessage; }
set
{
testMessage= value;
OnPropertyChanged("TestName");
}
}
public event PropertyChangedEventHandler PropertyChanged;
private void OnPropertyChanged(string propertyName)
{
if (PropertyChanged != null)
{
PropertyChanged(this, new PropertyChangedEventArgs(propertyName));
}
}
}
in your model you have the textMessage as being an int rather than string?
try something like this:
VIEWMODEL
private MyMessage message;
public MainViewModel()
{
message = new MyMessage();
}
public MyMessage Message
{
get { return message;}
set { message = value;}
}
//in your command:
this.Message.TestMessage = "Hello World!";
MODEL
public class MyMessage: INotifyPropertyChanged
{
private string testMessage
public string TestMessage;
{
get{ return testMessage; }
set
{
testMessage = value;
this.OnPropertyChanged("TestMessage");
}
}
//INotifyChanged Events
}
XAML
<TextBox Text="{Binding Message.TestMessage, Mode=TwoWay, UpdateSourceTrigger=PropertyChanged}"/>
I don't understand your code but I guess you should fix your binding with this:
<TextBox Name="MessageTextBox" Text="{Binding MyMessage.TestMessage}"/>
Where MyMessage should be a public property of MainViewModel
I want to bind a TextBox in the window to a property contained within a class that is a variable of the viewmodel and ensure that INotifyPropertyChanged's PropertyChanged event propagates from the class to the parent.
Let me illustrate with an example:
(Window's DataContext is set to an instance of ViewModel)
public class ViewModel {
private OtherClass classInstance = new OtherClass();
public int Attribute {
get { return classInstance.Attribute; }
}
}
public class OtherClass : INotifyPropertyChanged {
private int _attribute;
public int Attribute {
get { return _attribute; }
set {
_attribute = value;
PropertyChanged("Attribute");
}
}
...
}
The problem in this example is that, when Attribute changes, the bound Textbox does not update the binding since I assume it's listening to the ViewModel's PropertyChanged event and not that of the instance of OtherClass.
Any ideas on how to remedy this situation? I was thinking about chaining OtherClass's INotifyPropertyChanged to that of its parent, but there has to be a better way.
Why not bind directly to the class property instead of using a proxy?
public class ViewModel {
private OtherClass classInstance = new OtherClass();
public OtherClass MyOtherClass {
get { return classInstance; }
}
}
Then in your binding you can simply reference the property via the SubClass
{Binding MyOtherClass.Attribute}
A drop dead simple example, but it works!
The Code Behind:
public partial class MainWindow : Window {
private readonly SomeClass _someClass = new SomeClass();
public MainWindow() {
InitializeComponent();
DataContext = _someClass;
}
}
public class SomeClass: INotifyPropertyChanged {
private readonly SomeSubClass _mySubClass = new SomeSubClass();
public SomeSubClass MySubClass {
get { return _mySubClass; }
}
private String _name;
public String Name {
get { return _name; }
set {
_name = value;
OnPropertyChanged("Name");
}
}
//Property Change Stuff
}
public class SomeSubClass : INotifyPropertyChanged {
private String _name;
public String Name {
get {
return _name;
}
set {
_name = value;
OnPropertyChanged("Name");
}
}
//Property Change Stuff
}
The XAML:
<Window x:Class="JWC.Examples.WPF.MainWindow"
xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
Title="MainWindow">
<StackPanel>
<Label Content="Name" VerticalAlignment="Top" />
<TextBox Text="{Binding Name}" />
<Label Content="SubClass.Name" />
<TextBox Text="{Binding MySubClass.Name}" />
<Label Content="Bound to Name" />
<TextBlock Text="{Binding Name}" />
<Label Content="Bound to MySubClass.Name" />
<TextBlock Text="{Binding MySubClass.Name}" />
</StackPanel>
</Window>
You will need to do something like this:
public class ViewModel {
public ViewModel() {
classInstance = new OtherClass();
classInstance.PropertyChanged += HandleAttributeChanged;
}
private void HandleAttributeChanged(object Sender, NotifyPropertyChangedEventArgs args) {
PropertyChanged("Attribute");
}
}
I don't show it here, but you should also implement IDisposable and unsubscribe from the PropertyChanged event on your child, otherwise you will leak memory.
Alternatively you can expose the classInstance as a public property and set your binding to: ViewModel.classInstance. Note this needs to be a property and not the field itself.
I think the parent class should subscribe to the child propertyCahnged event..something like:
public class ViewModel
{
private OtherClass classInstance = new OtherClass();
public ViewModel()
{
classInstance.PropertyChanged += NotifyChildAttributeChanged;
}
public int Attribute
{
get { return classInstance.Attribute; }
}
}
NotifyChildAttributeChanged is basically a method that listens only to the "Attribute" property and fires a PropertyChanged notification of its own..
Of course our parent class must implement INotifyPropertyChanged as well as will all ViewModels (preferably) and your DataContext will detect the change.
To get around this you need to implement INotifyPropertyChanged on your view model as well. Just add the interface and the event and the rest will take care of itself - no need to chain the events / calls together.
Check out this for using reflection to get the property as well.
http://tsells.wordpress.com/2011/02/08/using-reflection-with-wpf-and-the-inotifypropertychanged-interface/