I am having some problems with a TextBox.Text binding in UWP. I have been doing WPF for years and typically know what I'm doing in XAML but can't get this binding to work...
I have a TextBox and a Button in the same scope in the XAML
<StackPanel Orientation="Horizontal"
Margin="0,10,0,0">
<TextBox Width="200" Text="{Binding SearchText, UpdateSourceTrigger=PropertyChanged}"/>
<Button Margin="10,0,0,0"
Command="{Binding SearchBusCommand}">Go</Button>
</StackPanel>
And the bound properties are in the same scope in the ViewModel
public ICommand SearchBusCommand { get; }
public string SearchText { get; set; }
But, when I type text in the TextBox and hit the Button, the command executes and the SearchText value is null...
My expectation is that when I type text into the TextBox the SearchText property is updated with the Text value.
If I set the value of the SearchText property from the ViewModel it does appear in the TextBox.
Ok it seems that in UWP the binding on the TextBox.Text property is OneWay by default..!
I had to set the binding to TwoWay to make it work.
<TextBox Width="200" Text="{Binding SearchText, Mode=TwoWay, UpdateSourceTrigger=PropertyChanged}"/>
WHY WOULD THEY DO THAT!?
Related
I am trying to create a list view where the background color alternates for each entry in the list. Is there a way to do this in MAUI?
This can be done in multiple ways.And the method often recommended is through a DataTemplateSelector.
1.Create a DataTemplateSelector that holds two templates and selects them based on the index of the item:
public class AlternateColorDataTemplateSelector: DataTemplateSelector
{
public DataTemplate EvenTemplate { get; set; }
public DataTemplate UnevenTemplate { get; set; }
protected override DataTemplate OnSelectTemplate(object item, BindableObject container)
{
// TODO: cast `Monkey` to your Item
return ((List<Monkey>)((ListView)container).ItemsSource).IndexOf(item as Monkey) % 2 == 0 ? EvenTemplate : UnevenTemplate;
}
}
2.In XAML, we can define two templates, one with the alternate color and one with the normal color.
<?xml version="1.0" encoding="utf-8" ?>
<ContentPage xmlns="http://schemas.microsoft.com/dotnet/2021/maui"
xmlns:x="http://schemas.microsoft.com/winfx/2009/xaml"
x:Class="MauiApp0606.MainPage"
xmlns:local="clr-namespace:MauiApp0606"
>
<ContentPage.Resources>
<ResourceDictionary>
<DataTemplate x:Key="evenTemplate">
<ViewCell>
<Grid BackgroundColor="White">
<Label Text="{Binding Name}" HorizontalOptions="Center" VerticalOptions="Center" />
</Grid>
</ViewCell>
</DataTemplate>
<DataTemplate x:Key="unevenTemplate">
<ViewCell>
<Grid BackgroundColor="LightGray">
<Label Text="{Binding Name}" TextColor="White" HorizontalOptions="Center" VerticalOptions="Center" />
</Grid>
</ViewCell>
</DataTemplate>
<local:AlternateColorDataTemplateSelector x:Key="alternateColorDataTemplateSelector"
EvenTemplate="{StaticResource evenTemplate}"
UnevenTemplate="{StaticResource unevenTemplate}" />
</ResourceDictionary>
</ContentPage.Resources>
<VerticalStackLayout Spacing="25" Padding="30">
<ListView ItemsSource="{Binding Monkeys}" ItemTemplate="{StaticResource alternateColorDataTemplateSelector}">
</ListView>
</VerticalStackLayout>
</ContentPage>
To solve this problem I added a LineNumber property to my view model and used a value converter to set the color.
The value converter:
public class NumberToAlternatingColorValueConverter : IValueConverter
{
public Color EvenNumberColor { get; init; } = Colors.Green;
public Color OddNumberColor { get; init; } = Colors.Red;
public object Convert(object value, Type targetType, object parameter, CultureInfo culture)
{
return value is not int intValue
? Colors.Transparent
: (intValue % 2) == 0
? EvenNumberColor
: OddNumberColor;
}
public object ConvertBack(object value, Type targetType, object parameter, CultureInfo culture)
{
throw new NotImplementedException("NumberToAlternatingColorValueConverter.ConvertBack");
}
}
Register the value converter
I registered the value converter in my main resource dictionary like so:
<converter:NumberToAlternatingColourValueConverter
x:Key="MagentaCyanRowColorConverter"
EvenNumberColour="Magenta"
OddNumberColour="Cyan" />
You can register more than one value converter with a different key for different colour combinations.
Use the value converter
And I used the bound value converter in my XAML like so:
<StackLayout BindableLayout.ItemsSource="{Binding Summary.Lines}">
<BindableLayout.ItemTemplate>
<DataTemplate x:DataType="vm:SummaryLineViewModel">
<Grid BackgroundColor="{Binding LineNumber, Converter={StaticResource MagentaCyanRowColorConverter}}">
<Label Grid.Column="0" Text="{Binding Name}" />
<Label Grid.Column="1" Text="{Binding Value}" />
</Grid>
</DataTemplate>
</BindableLayout.ItemTemplate>
</StackLayout>
As in this answer we can used DataTemplateSelector to resolve your problem.
Alternative solutions,
You can use a property in the model and straight a way bind it to the row background. (In your case Grid's Background color)
You can use triggers make the color change by considering a logic.
( Xamarin Forms Triggers )
I have ContentView which need ViewModel binding
Test.xaml
<ContentView.Content>
<Frame x:Name="HelpBaseFrame" BackgroundColor="White" CornerRadius="16" HorizontalOptions="Fill" VerticalOptions="Center">
<StackLayout>
<ListView HasUnevenRows="True" x:Name="lstview" SeparatorColor="White">
<ListView.ItemTemplate>
<DataTemplate>
<ViewCell IsEnabled="False">
<ScrollView x:Name="ScrollView" Orientation="Vertical" Padding="0, 1, 0, 0" BackgroundColor="Transparent" HorizontalOptions="Center">
<StackLayout>
<Label x:Name="LabelHeader" FontAttributes="Bold" Font="HiraginoSans-W6, 16"
HorizontalOptions="Center" Margin="0,20,0,0">
<Label.Text>
<Binding Path="HeaderData"></Binding>
</Label.Text>
</Label>
<local:LineSpacingLabel x:Name="LabelHeaderDesceiption" LineSpacing="6"
Font="HiraginoSans-W3, 16" FontAttributes="None" Margin="0,20,0,0">
<Label.Text>
<Binding Path="DescriptionData"></Binding>
</Label.Text>
</local:LineSpacingLabel>
</StackLayout>
</ScrollView>
</ViewCell>
</DataTemplate>
</ListView.ItemTemplate>
</ListView>
</StackLayout>
</Frame>
</ContentView.Content>
BindingClass
public void SetData(Dictionary<string, string> dictionary)
{
............
lstview.ItemsSource = HelpDataList; // HelpDataList is observable collection of HElp Data
}
Model class :
public class HelpData : BaseViewModel
{
private string Header = string.Empty;
private string Description = string.Empty;
public string HeaderData
{
get { return Header; }
set
{
Header = value;
OnPropertyChanged("HeaderData");
}
}
public string DescriptionData { get; set; }
}
This view model for above view.
This binding is not working.
Is anything wrong?
This view model for above view.
This binding is not working.
Is anything wrong?
This view model for above view.
This binding is not working.
Is anything wrong?
You have to set bindingContext on the target control by using x:Reference markup extension.
BindingContext="{x:Reference Name=ViewModelField}"
Or
BindingContext="{x:Reference ViewModelField}"
Label.Text should be binding with string not viewModel.
Text="{Binding Path=Value}"
Or
Text="{Binding Value}" ( “Path=” part of the markup extension can be omitted if the path is the first item in the Binding markup extension)
Refer to Bindings
Update
<Binding> is not a valid tag.
Modify the label :
<Label Text="{Binding Path = HeaderData}">
I have FlipView like this
<FlipView Grid.Row="1" Grid.RowSpan="2" HorizontalContentAlignment="Center" x:Name="BookPageContentFlipView" ItemsSource="{Binding BookPagesNew,Mode=OneWay}"
SelectedItem="{Binding SelectedPage,Mode=TwoWay}"
SelectionChanged="BookPageContentFlipViewSelectionChanged" >
<FlipView.ItemsPanel>
<ItemsPanelTemplate>
<VirtualizingStackPanel Background="Transparent" Orientation="Horizontal"
VirtualizationMode="Recycling" AreScrollSnapPointsRegular="True" />
</ItemsPanelTemplate>
</FlipView.ItemsPanel>
<FlipView.ItemTemplate>
<DataTemplate>
<Grid HorizontalAlignment="Center" Width="650" x:Name="GridWebView">
<WebView
common:HTMLStringExtension.HTML="{Binding HTMLString}"
ScriptNotify="OnBookPageContentWebViewScriptNotify"
Tapped="OnBookPageContentFlipViewTapped" />
<Image Source="ms-appx:///Assets/add-bookmark.png" x:Name="BookmarkImage"
Tapped="OnBookmarkImageTapped" HorizontalAlignment="Right" VerticalAlignment="Top"
Width="38"
Height="38" />
</Grid>
</DataTemplate>
</FlipView.ItemTemplate>
</FlipView>
I am using MVVM and update this flipview ItemsSource from VM. Now my problem is when I am update ItemsSource from VM and use NotifyPropertyChanged() to notify View to update the flipview ItemsSource, my selected flipview not updating the view with new data.
But after I move about > 2 item (next/previous) item the view correctly updated. How I can force my flipview to update the currently selected item without need to reload flipview?
I think that BookPagesNew needs to implement the interface INotifyPropertyChanged
because if you change only one property of an item in a list the view doesn't get the notification.
you can use this code to implement the interface
public class BookPagesNew : INotifyPropertyChanged
{
public string HTMLString { get; set; }
public event PropertyChangedEventHandler PropertyChanged;
public void RaisePropertyChanged(string propertyName)
{
if (PropertyChanged != null)
{
PropertyChanged(this, new PropertyChangedEventArgs(propertyName));
}
}
}
in your VM BookPagesNew should be an ObservableCollection<BookPagesNew>
I have a Silverlight 4 app created in MVVMLight.
In a view I have a DataGrid that is bound to my ViewModel, which has SeletedItem bound to SelectedItem again in my ViwModel :
<sdk:DataGrid Name="MyGrid" AutoGenerateColumns="False" Grid.Row="3" MaxHeight="200" HorizontalAlignment="Left" Margin="0,0,0,0" VerticalAlignment="Top" RowHeight="35"
SelectedItem="{Binding SelectedItem, Mode=TwoWay, ValidatesOnNotifyDataErrors=False}" ItemsSource="{Binding Items}" >
This all works just as it should as in when I click on an item in the grid the SelectedItem in my ViewModel is set correctly.
Now I have added a button to the rows in the Datagrid and added an EventToCommand to the button which is bound to the same ViewModel:
<Button Content="Update" >
<i:Interaction.Triggers>
<i:EventTrigger EventName="Click">
<Command:EventToCommand Command="{Binding Source={StaticResource Locator}, Path=MainDialog.ButtonCommand, Mode=TwoWay}" />
</i:EventTrigger>
</i:Interaction.Triggers>
This command fires and works correctly The Problem Is the SelectedItem property that was set earlier, that I now want to use is set to null!!
Why is this EventToCommand resetting the SelecteedItem property and how do I stop it so I can use it???
you should shar your code to let us see what the problem is. But maybe problem is that you set selected item as object that isn't in your itemsource collection of datagrid. Try to set selecteditem like this
SelectedItem = Items.Where(x => x.Id == someId).First();
And see if this is the problem.. Ofcourse change condition in Where.. :)
In my scenario I have a MainView + MainViewModel, UserControl1 + UserControl 2.
In the MainView I have 2 buttons labeled: Button_ShowUserControl1 + Button_ShowUserControl2.
At the lower part of the MainView I have a "ContentGrid" which takes/should_take... every UserControl.
My goal:
When Button_ShowUserControl1 is clicked UserControl1 is Visible and UserControl2 OR any other UserControl must be set to Collapsed. Same is valid for Button_ShowUserControl2.
My problem:
1.) As the UserControls shall be loaded at application start how can I put them all together in the one "ContentGrid"? Thats actually not possible... so how can I make one UserControl visible while the other is in the same place/"ContentGrid" just collapsed ?
2.) As 1.) seems not possible how can I instantiate all UserControls at start of the application and make them only Visible/Collapsed when respective Button is clicked?
3.) As a UserControl has a property Visibility = Visible/Hidden/Collapsed, how can I bind to a property in a ViewModel return such a value like Collapsed? I only could get a boolean value like Visibility = false/true ?
My testcode:
<Grid x:Name="LayoutRoot" Background="#FFBDF5BD" ShowGridLines="False">
<Grid.RowDefinitions>
<RowDefinition Height="96*" />
<RowDefinition Height="289*" />
</Grid.RowDefinitions>
<Grid HorizontalAlignment="Stretch" Name="MenuGrid" VerticalAlignment="Stretch" Background="#FFCECEFF">
<StackPanel Name="stackPanel1" Background="#FFEDFF00" Orientation="Horizontal">
<Button Content="User Data 1" Height="35" Name="button1" Command="{Binding Path=ShowUserControl1Command}" Width="150" Margin="100,0,0,0" />
<Button Content="User Data 2" Height="35" Name="button2" Width="150" Margin="100,0,0,0" />
</StackPanel>
</Grid>
<Grid Grid.Row="1" HorizontalAlignment="Stretch" Name="ContentGrid" VerticalAlignment="Stretch" Background="#FFB15454" />
</Grid>
<UserControl x:Class="SwapUserControls.MVVM.UserControl2"
xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006"
xmlns:d="http://schemas.microsoft.com/expression/blend/2008"
xmlns:vm="clr-namespace:SwapUserControls.MVVM.ViewModel"
mc:Ignorable="d"
d:DesignHeight="300" d:DesignWidth="300" Visibility="{Binding IsUserControl1Collapsed, Path=Value}">
<UserControl.Resources>
<vm:MainViewModel x:Key="MainViewModelID" />
</UserControl.Resources>
<UserControl.DataContext>
<Binding Source="{StaticResource MainViewModelID}" />
</UserControl.DataContext>
<Grid>
<Grid.RowDefinitions>
<RowDefinition Height="228*" />
<RowDefinition Height="72*" />
</Grid.RowDefinitions>
<Button Content="UserControl2" Grid.Row="1" Height="23" HorizontalAlignment="Left" Margin="112,27,0,0" Name="button1" VerticalAlignment="Top" Width="75" />
<DataGrid HorizontalAlignment="Stretch" Name="dataGrid1" VerticalAlignment="Stretch" Background="#FFC046F8" />
</Grid>
public class MainViewModel : ViewModelBase
{
RelayCommand _ShowUserControl1Command;
private bool _IsUserControl1Collapsed;
public RelayCommand ShowUserControl1Command
{
get
{
if (_ShowUserControl1Command == null)
{
_ShowUserControl1Command = new RelayCommand( () => ShowUserControl1() );
}
return _ShowUserControl1Command;
}
}
public void ShowUserControl1()
{
_IsUserControl1Collapsed = true;
}
public bool IsUserControl1Collapsed
{
get
{
return _IsUserControl1Collapsed;
}
}
}
Yes the code is wrong, therefore I ask here :)
You only have 2 things wrong with this code.
1) You can't set the visibility of a usercontrol directly... you have to set it on a container:
<Grid Visibility="Collapsed">
<myControls:MyUserControl />
</Grid>
2) Visibility is not a boolean value, it is an enum. As such, you will need to use a converter to convert from boolean to Visibility. Observe:
<Window ...>
<Window.Resources>
<BooleanToVisibilityConverter x:Key="BoolToVis" />
</Window.Resources>
<Grid Visibility="{Binding ShouldShowUsercontrol1, Converter={StaticResource BoolToVis}}">
<myControls:MyUserControl />
</Grid>
</Window>
That should be it. Hope this helps.
There are other things that you are leaving clues about that might affect the ability of this to work. For example, you don't show the biggest container element... are you wrapping everything in a StackPanel? If you are wrapping everything in a Grid, for example, the controls will overlay everything in layers.
Try these changes I suggest... it should get you closer.
Edit: Another idea using data templates
Another thing you could do is make sure you have a unique ViewModel for each of these views you want to show and hide:
public class MyFirstViewModel : ViewModel
{
}
public class MySecondViewModel : ViewModel
{
}
Then from your "parent" or "main" ViewModel, you show or hide the views you want by virtue of having them in a collection of ViewModels:
public MyMainViewModel : ViewModel
{
public ObservableCollection<ViewModel> ViewsToShow
{
...
}
public void ShowFirstViewModel()
{
ViewsToShow.Add(new MyFirstViewModel());
}
}
To wire everything up in your view, you would then datatemplate these types with their user controls (but this would not cause those views to be instantiated unless they were needed:
<Window ...>
<Window.Resources>
<DataTemplate DataType="{x:Type myViewModels:MyFirstViewModel}">
<myViews:MyFirstView />
</DataTemplate>
<DataTemplate DataType="{x:Type myViewModels:MySecondViewModel}">
<myViews:MySecondView />
</DataTemplate>
</Window.Resources>
<ItemsControl ItemsSource="{Binding ViewsToShow}" />
</Window>
And for any ViewModels you put in "ViewsToShow", the view will automatically see that and template in the appropriate view. Again, without instantiating it before it's needed.
This is probably a little cleaner than putting everything single thing in the View and setting visibility, but it would be dependent on you have a unique view model type for every view, which might not be the case.
The question of saving state comes up when using the DataTemplated approach. The solution here is to tread your ViewModel as the state of the control and design both your ViewModels and your Views accordingly. Here is an example that allows you to swap out your Views using DataTemplating, but switching back and forth saves state.
Assume you have the setup from the last section w/ 2 viewmodels that have datatemplates defined. Let's change up the MainViewModel a little:
public MyMainViewModel : ViewModel
{
public RelayCommand SwapViewsCommand
{
...
}
public ViewModel View
{
...
}
private ViewModel _hiddenView;
public MyMainViewModel()
{
View = new MyFirstViewModel();
_hiddenView = new MySecondViewModel();
SwapViewsCommand = new RelayCommand(SwapViewModels);
}
public void SwapViewModels()
{
var hidden = _hiddenView;
_hiddenView = View;
View = hidden;
}
}
And a few changes to the main view. I've omitted the DataTemplates for brevity.
<Window ...>
<!-- DataTemplates Here -->
<Button Command="{Binding SwapViewsCommand}">Swap!</Button>
<ContentControl Content="{Binding View}" />
</Window>
That's it. The secret here is I'm saving the reference to the original view model. This way, let's say there is a string property in a viewmodel and an associated textbox in the DataTemplated usercontrol with a two-way binding then the state will essentially be saved.