It works fine:
<Button Width="100" Height="30" Content="Click Me!">
<Button.ToolTip>
<Border Margin="-4,0,-4,-3" Padding="10" Background="Silver">
<Border.BitmapEffect>
<OuterGlowBitmapEffect></OuterGlowBitmapEffect>
</Border.BitmapEffect>
<Label>Nice tooltip</Label>
</Border>
</Button.ToolTip>
</Button>
However, I would like the code to revoke when there is a condition. For example:
if(str=="aaa")
MessageBox.Show("All will be o'kay");
else
{
//I would like this code to revoke
/* <Border.BitmapEffect>
<OuterGlowBitmapEffect></OuterGlowBitmapEffect>
</Border.BitmapEffect>
*/
}
How to do it?
Just create a property which raises notification . You can implement INotifyPropertyChanged Interface. Change value of property in code and bind it with xaml.
Related
I'm trying to display some text -- or an image -- if there's no data for my ListView to display in my Xamarin Forms 5 app but I can't get it to work.
Here's what my ListView looks like:
<ListView
x:Name="CustomersList"
ItemsSource="{Binding Customers, TargetNullValue='No customers!'}"
BackgroundColor="Transparent">
<ListView.ItemTemplate>
<DataTemplate>
<TextCell
Text="{Binding FullName}"
TextColor="{StaticResource PrimaryDark}"
Command="{Binding Source={x:Reference Name=CustomersList}, Path=BindingContext.CustomerSelectedCommand}"
CommandParameter="{Binding .}"/>
</DataTemplate>
</ListView.ItemTemplate>
</ListView>
The source for the ListView is set as follows in my ViewModel
ObservableRangeCollection<CustomerModel> customers;
public ObservableRangeCollection<CustomerModel> Customers
{
get => customers;
set
{
if (customers == value)
return;
customers = value;
OnPropertyChanged();
}
}
If my API call returns nothing, I do a Customers = null;
When I use TargetNullValue as shown above, I acutally get errors where I bind the TextCell to FullName. It shows:
'FullName' property not found on 'N', target property:
'Xamarin.Forms.TextCell.Text'
It then repeats this error message for every character in No Customers!.
I then tried using FallbackValue. This time I don't get an error but it simply doesn't show the "No Customers!" message.
How do I handle a ListView having no data to show? At the very least, I'd like to show some simple text message but it would be even better to show something nicer, maybe an image.
If you are ok to switch from ListView to CollectionView, you can use the built-in CollectionView.EmptyView:
<CollectionView ItemsSource="{Binding Customers}"
EmptyView="No customers!" ... />
With the same EmptyView you can define whatever view:
<CollectionView>
<CollectionView.EmptyView>
<ContentView>
<image ... />
</ContentView>
</CollectionView.EmptyView>
</CollectionView>
Docs: CollectionView EmptyView
I'm working on a view (called 'Familify') which shows users a list of assets, and allows them to delete an asset from the list. The assets are stored in an ObservableCollection in the ViewModel, so the command to delete simply takes the asset object and removes it from collection. I'm having issues getting the 'delete' functionality working. Here is the XAML and codebehind:
Familify.xaml
<ListView
ItemsSource="{Binding Assets}">
<ListView.ItemTemplate>
<DataTemplate>
<Grid>
<Grid.ColumnDefinitions>
<ColumnDefinition Width="80px" />
<ColumnDefinition Width="*" />
<ColumnDefinition Width="150px" />
<ColumnDefinition Width="*" />
<ColumnDefinition Width="60px" />
</Grid.ColumnDefinitions>
<TextBlock
Grid.Column="0"
Text="{Binding number}" FontFamily="Consolas"/>
<TextBlock
Grid.Column="1"
Text="{Binding type}"/>
<TextBlock
Grid.Column="2"
Text="add binding here"/>
<TextBlock
Grid.Column="3"
Text="add binding here"/>
<Button
Command="{x:Bind ViewModel.RemoveAssetCommand}"
CommandParameter="{Binding}"
Content=""
FontFamily="Segoe MDL2 Assets"
Grid.Column="4">
</Button>
</Grid>
</DataTemplate>
</ListView.ItemTemplate>
</ListView>
Familify.xaml.cs
namespace asset_manager.Views
{
public sealed partial class Familify : UserControl
{
FamilifyViewModel ViewModel { get; set; }
public Familify()
{
this.InitializeComponent();
DataContextChanged += (s, e) =>
{
ViewModel = DataContext as FamilifyViewModel;
};
}
}
}
The idea is that clicking the button removes the asset from the list. (Just to note, the normal binding showing number, type, etc. is working correctly.) My thinking so far:
Try to use binding to access the RemoveAssetCommand stored in the View Model for the page. However, I couldn't get ancestral binding to work (i.e. trying to find the data context of an element higher up in the XAML hierarchy didn't work because findAncestor isn't a thing in UWP.)
x:Bind looked like a good solution, because it uses an explicit path to the property. So, if I declared ViewModel in my code behind, I could use x:Bind ViewModel.property. All well and good. I did just that, and intellisense allowed me to access the ViewModel.RemoveAssetCommand when typing it out.
However, this did not work, because I get the error no DataType defined for DataTemplate. This makes sense, so I tried two things.
x:DataType="Models:Asset" (put in the DataTemplate tag above) is the model being shown in the data template, so I tried that first. Of course, the command is not declared in the model, it's declared in the View Model, so that didn't work.
I instead tried x:DataType="ViewModels:FamilifyViewModel", thinking I could just use x:Bind with that. However, I then got an error that it couldn't cast an object of type Asset to FamilifyViewModel. This makes sense, because the object getting passed to this data template is of the type Asset.
This is a pain, because the whole reason I thought x:Bind would work is that I could just access the property directly from the ViewModel in the codebehind.
Explicitly stated, 1) is it possible to use x:Bind within a data template to access a base level property (in this case, a Prism command) on the ViewModel? and 2) is there a better way to go about implementing this functionality?
Is it possible to use x:Bind within a data template to access a base level property (in this case, a Prism command) on the ViewModel?
Yes, if you want to access a base level, you can reassign DataContext of button like following:
<Button DataContext="{Binding ElementName=Familily, Path=DataContext}"/>
The Family is the name of UserControl.
is there a better way to go about implementing this functionality?
When you put commad in the ViewModel and bind the button as above. The the bind item of button will become Family DataContext. So you could not invoke delete action directly in the ViewModel.
The best practice to implement this functionality is that put the RemoveAssetCommand in the Asset class. And use the ItemsSource of ListView as Button CommandParameter.
<Button
Command="{Binding RemoveAssetCommand}"
CommandParameter="{Binding ElementName=MyListView, Path=ItemsSource}"
Content=""
FontFamily="Segoe MDL2 Assets"
Grid.Column="4">
</Button>
Asset.cs
public class Asset
{
public string number { get; set; }
public string type { get; set; }
public ICommand RemoveAssetCommand
{
get
{
return new CommandHandler<ObservableCollection<Asset>>((item) => this.RemoveAction(item));
}
}
private void RemoveAction(ObservableCollection<Asset> items)
{
items.Remove(this);
}
}
ViewModel.cs
public class FamilifyViewModel
{
public ObservableCollection<Asset> Assets = new ObservableCollection<Asset>();
public FamilifyViewModel()
{
Assets.Add(new Asset { number = "100001", type = "hello" });
Assets.Add(new Asset { number = "100001", type = "hello" });
Assets.Add(new Asset { number = "100001", type = "hello" });
Assets.Add(new Asset { number = "100001", type = "hello" });
}
}
I have a UserControl with a button inside it. The UserControl its DataContext is one of my models so I can bind to it. However, for the button I want to be able to call a method from my viewmodel. The DataContext of the ListBox is this ViewModel.
Because my ContextMenu also needs the same DataContext I've bound them like this:
Command="{Binding Path=DataContext.AttendEventCommand, ElementName=EventListBox}"
Calling the EventListBox element and using its DataContext to call the AttendEventCommand. However I would like to call the AttendEventCommand from a button on the UserControl. I tried doing it the same way but sadly it doesn't work.
My data context is set like this:
DataContext="{Binding Path=EventList, Source={StaticResource Locator}}
My listbox code:
<ListBox x:Name="EventListBox" ItemsSource="{Binding Occurrences}" Margin="0,50,0,0" >
<ListBox.ItemTemplate>
<DataTemplate>
<Grid>
<uctl:EventListItem HorizontalAlignment="Stretch" VerticalAlignment="Stretch" Width="auto" Height="auto">
<toolkit:ContextMenuService.ContextMenu>
<toolkit:ContextMenu IsZoomEnabled="True" x:Name="ContextMenu">
<toolkit:MenuItem x:Name="Going" Header="{Binding AttendingText}" Command="{Binding Path=DataContext.AttendEventCommand, ElementName=EventListBox}" CommandParameter="{Binding}"/>
</toolkit:ContextMenu>
</toolkit:ContextMenuService.ContextMenu>
</uctl:EventListItem>
</Grid>
</DataTemplate>
</ListBox.ItemTemplate>
</ListBox>
And my UserControl's button:
<Button Grid.RowSpan="3" Grid.Column="5" Opacity="0" Command="{Binding Path=DataContext.AttendEventCommand, ElementName=EventListBox}" CommandParameter="{Binding}"/>
I believe your problem is not that what you want to do is not working; instead, your design appears to be wrong.
What you have now is like this:
You have a Window that has a DataContext and a ListBox. The ListBox has an ItemsSource, which we'll assume is some IEnumerable<Occurrence>.
The appearance of each item in your ListBox is an EventListItem, which is a UserControl that contains at least one Button.
You want this Button's Command to call a method on your Window's DataContext.
This last sentence is wrong. The fact that the item has the button implies that it does something that is related to the item, not the window contents. If this is not true, then the visual design of the window and listbox items should probably be reconsidered.
If the button is in fact affecting the item, then you should not call a method on your Window's DataContext, but instead call a method on your item's DataContext.
The solution is to wrap your model object Occurrence in a view model class of its own. Let's call it OccurrenceViewModel. Your ListBox's ItemsSource would be some form of IEnumerable<OccurrenceViewModel>. Because it's a view model, it's allowed to implement Command methods, which can then in one way or another manipulate the Occurrence, either directly or preferably by passing it to some class that implements the use case.
The DataContext of your EventListItem will be a Model of your ItemsSource because it is part of the DataTemplate. So you have to set it explicitly.
Refer to How to implement a navigation button for some of the code I'll be using as a solution.
Lets assume your custom UserControlis very basic like so:
<UserControl>
<Grid x:Name="LayoutRoot" Background="{StaticResource PhoneChromeBrush}">
<Button Command="{Binding DataContext.SimpleCommand}" CommandParameter="1"></Button>
</Grid>
</UserControl>
Where SimpleCommand is the Command you want to call in the Top View Model.
Then you have to change your DataTemplate to
<DataTemplate>
<Grid>
<uctl:EventListItem
DataContext="{Binding ElementName=myListBox}"/>
<!-- more xaml -->
</Grid>
</DataTemplate>
Your <toolkit:ContextMenu> should work as is.
Put a break point at the Execute function of the ICommand and you will see it will get
hit there everytime.
public void Execute(object parameter)
{
// logic to execute when user hits the command
int debug_var = 0; // put a break point here
}
I have the following piece of XAML:
<GroupStyle.HeaderTemplate>
<DataTemplate>
<Grid Background="#286C9A" Width="336" Height="22">
<TextBlock Text="{Binding Checked}" Foreground="Black" HorizontalAlignment="Left"/>
<CheckBox IsChecked="{Binding Checked}" HorizontalAlignment="Right" />
</Grid>
</DataTemplate>
</GroupStyle.HeaderTemplate>
It's a template in a ListView. Checked is a bool property, and the problem is that the initial value of the property is transferred correctly to the view (both TextBlock and CheckBox). But following changes to the property is only reflected on the TextBlock, the Checkbox does not react.
Can someone tell me what happens?
EDIT:
The relevant part (I believe) of the ViewModel is this :
public class MenuGroup : ObservableCollection<MenuItem>
{
bool #checked;
public bool Checked
{
get { return #checked; }
set
{
if (#checked == value) return;
#checked = value;
OnPropertyChanged(new PropertyChangedEventArgs("Checked"));
}
}
}
EDIT: It is apparent that the binding stops working the first time I have clicked on the checkbox and thus manually changed it's state. And it works all the way if it's TwoWay binding. But why that is, I don't know.
I have a windows phone 7 app with some xaml that looks like:
<Grid x:Name="ContentGrid" Grid.Row="1">
<ItemsControl x:Name="MyView" ItemTemplate="{StaticResource MyInner}"/>
</Grid>
The item template here looks like:
<DataTemplate x:Key="MyInner">
<ItemsControl ItemsSource="{Binding}" ItemTemplate="{StaticResource MyInner_Item}">
<ItemsControl.ItemsPanel>
<ItemsPanelTemplate>
<StackPanel Orientation="Horizontal"/>
</ItemsPanelTemplate>
</ItemsControl.ItemsPanel>
</ItemsControl>
</DataTemplate>
And finally, the MyInner_Item template looks like:
<DataTemplate x:Key="MyInner_Item">
<Button x:Name="MyButton">
<Button.Template>
<ControlTemplate>
<Border HorizontalAlignment="Center" VerticalAlignment="Center" x:Name="myborder">
<Image Source="{Binding Path=ImageUri}" Width="{Binding Path=Width}" Height="{Binding Path=Height}" Stretch="Fill" />
</Border>
</ControlTemplate>
</Button.Template>
</Button>
</DataTemplate>
So, it's an ItemsControl, which contains an ItemsControl, which contains buttons. This essentially creates a 2D array of buttons.
What I want to do is add an event handler to the Click event of the buttons.
Here's the catch: the code that sits behind this is written in F#. I can't, to the best of my knowledge, specify my event handler in the XAML, as F# doesn't talk to WPF in any nice way. So I need to add my event handler(s) manually in code.
Is there an easy way of doing this?
Currently, I have some F# which looks like:
let myView : ItemsControl = this?MyView
do myView.ItemsSource <- viewModel.BoardData
Here, the BoardData is a list of lists.
I was wondering if it's possible to loop through the controls in the ItemsControl, to add my event handlers? I'm having a bit of trouble doing this though. For example, in the following:
let container = myView.ItemContainerGenerator.ContainerFromItem(myView.Items.[0])
...sets container to null. In fact, all the methods I've tried from myView.ItemContainerGenerator returns null.
So, how should I go about attaching my event handler, so that I can respond to the buttons being clicked?
I have not done any Windows 7 Phone development, but I have done plenty of XAML + Silverlight development with C# and now I'm getting into doing some F# development. The approach I would take is by not using event handler's at all. Since you are using a button, make a class that derives from ICommand and add that type as a public property on your ViewModel so you could bind it to the Command property of the button. The benefits of using the ICommand interface over event handlers is that you could also have a condition on when the button is enabled to do the action.
Also, take notice that when you are doing binding expressions within (i.e. ItemTemplate) items in an ItemsControl control, the scope of what properties you can bind to are reduced to the properties of the current item. So all of the properties of the ViewModel are out of scope, unless you specify it fully i.e. <Button Command={Binding Source=ViewModel, Path=Property1.Property2.etc} />. Let me know if this helped.