I have defined a XAML page for my WP8 app that currently holds a LongListSelector with an ItemTemplate.
I'm outputting some personal info like name and age. Each is a TextBlock defined like so:
<TextBlock Text="{Binding Age, StringFormat='Age: {0}'}" Visibility="{Binding AgeVisibility}"/>
The thing is that the user doesn't always input all the data, so sometimes some attributes are missing (like age). In those cases I would like to remove the TextBlock.
With the code defined like it is (note the use of the Visibility attribute) it only hides the element, which leaves an ugly space in the form.
Is there a way to remove an element from the list, if it might be undefined/missing?
EDIT: I should note that while I do use a LongListSelector, it only actually holds a single element. This element is then binded to a pure data class with many properties:
public class Details
{
public string Name { get; set; }
public string Age { get; set; }
}
I would recommend creating an ObservableCollection of objects you'd like to bind, and adding it to the LongListSelector like this:
longListSelector.ItemsSource = myCollection;.
Everytime you'd like to remove an element from the list, you'd just call something like myCollection.RemoveAt(0) and the list will update itself.
Related
I am using the TreeView control from the WinrtXamlToolkit in a uwp app. I want to apply a different style to some TreeViewItems depending on a conditon so I created a class, TreeViewItemStyleSelector which derives from StyleSelector and I override the SelectStyleCore function.
public Style ResourceStyle { get; set; }
public Style ClassroomStyle { get; set; }
protected override Style SelectStyleCore(object item, DependencyObject container)
{
// control never reaches here.
// logic to apply style
}
Then in xaml I use it like this.
In Page Resources
<StyleSelectors:TreeViewItemStyleSelector ResourceStyle="{StaticResource AStyle}" ClassroomStyle = "{StaticResource BStyle}"/>
And later in the page.
<wxtControls:TreeView ItemsSource="{Binding StructureViewModels}" ItemContainterStyleSelector="{StaticResource TreeViewItemStyleSelector}" />
The problem is that the SelectStyleCore override is never called. Does anybody know why?
I am not yet sure what's the reason this doesn't work, although I have some theories. One is - this was never implemented. Perhaps at least at the root level it should work because it's an ItemsControl, but because of the way it's implemented (hierarchically) - the ItemContainerStyleSelector would have to be forwarded from the TreeView to the TreeViewItems, which it isn't.
I haven't had a chance to try to reproduce it yet, but if I were to try to fix it or work around it - I would first try forwarding that property in HeaderedItemsControl.cs - roughly where it says "// Note: this is where we would apply the HeaderTemplateSelector (...) (if implemented)". The alternative (if you don't want to modify the toolkit's code) might be to specify the template for the TreeViewItem and in the template - use a StyleSelector on template parts you want to be different for different data items.
Subj, how can i get it?
<controls:Pivot.TitleTemplate>
<DataTemplate>
<mainPivot:MyUserControl Name="MainPivotHeader"/>
</DataTemplate>
</controls:Pivot.TitleTemplate>
Tried to find it via VisualTreeFinders, but it sees only pivot item.
UserControl shows a picture, but it depends on user. During first initialization, it is empty, because user is not yet logged in. So, i'd like to force its update.
I can use mvvm light messaging, but i'm looking for self-sufficient components. This forcing is rare, so i dont want to use messaging here.
You should bind the Title property of the Pivot to a property on a ViewModel. Your DataTemplate would then have it's DataContext already set to that object. When you need to refresh, you call some method on that object.
Example
public class ViewModel : INotifyPropertyChanged
{
private MyTitleObject _titleObject;
public MyTitleObject TitleObject
{
get { return _titleObject; }
set
{
_titleObject = value;
OnPropertyChanged("TitleObject");
}
}
public void Refresh()
{
TitleObject = new MyTitleObject();
// or refresh values directly on the object
}
...
}
You xaml for your Pivot would need to following
<controls:Pivot Title="{Binding TitleObject}">
</controls:Pivot>
When you want to refresh, call the refresh on the viewmodel.
I am beginner in silverlight and all this mvvm pattern is bit confusing.
In my application I have two listboxs one for country and one for states.
What I want to do is when I select a Country from the listbox1 second listbox will display states from the selected country.
i.e I want to bind command in xaml to listboxitem.
I try to find the solution by Google but either solutions was too complex for me to understand or using different mvvm pattern like prism,light etc.
There are a few different ways of doing this:
1: (Easiest!) Bind the SelectedItem of the first ListBox to your ViewModel. In the Setter for the ViewModel property, change the list that you're binding to the second listbox. Note that your ViewModel property will need to use INotifyPropertyChanged to notify that the list has changed.
Eg: If your xaml looks like:
<ListBox ItemSource="{Binding ListOne}" SelectedItem="{Binding SelectedItem, Mode=TwoWay}"/>
<ListBox ItemSource="{Binding ListTwo}"/>
Then your ViewModel might be a bit like:
public List<MyItem> ListOne { get; set; }
private MyItem _selectedItem
public MyItem SelectedItem
{
get { return _selectedItem; }
set
{
_selectedItem = value;
ListTwo = _selectedItem.SubItems;
}
}
private List<MyOtherItem> _listTwo
public List<MyOtherItem> ListTwo
{
get { return _listTwo; }
set
{
_listTwo = value;
RaisePropertyChanged("ListTwo");
}
}
2: If the data for the second list is literally a property of the items in the first list, you can use an Binding in xaml to directly join them up.
ItemSource="{Binding Path=SelectedItem.MyItemsProperty, ElementName=MyFirstListBoxName}"
3: You can use an EventTrigger with an EventToCommand to turn the SelectedItemChanged event into a Command execution. You're not literally binding a command to the ListBoxItem, you're binding the command to the change.
I would recommend the first option, it's easiest and gives you good control of what's going on without getting too complicated.
How do you disable the selection single item from a GridView?
I have a GridView with it's ItemsSource bound to an IEnumerable<SampleDataItem>. I'd like to be able to programmatically not allow the selection of some items in the list while allowing selection of the others.
While I haven't done this, you should be able to use an ItemContainerStyleSelector on the GridView, the method gives you the container (GridViewItem) and the item you're binding to. From there you can set the IsEnabled property on the GridViewItem to false which makes it unselectable.
You'll also probably need to select a custom style as well since the default GridViewItem style will customise how a disabled item will look.
Update DataTemplateSelector Solution
public class IssueGridTemplateSelector : DataTemplateSelector
{
protected override DataTemplate SelectTemplateCore(object item, DependencyObject container)
{
var selectorItem = container as SelectorItem;
if (item is Issue)
return IssueTemplate;
selectorItem.IsEnabled = false;
selectorItem.Style = RepositoryItemStyle;
return RepositoryTemplate;
}
public DataTemplate IssueTemplate
{
get;
set;
}
public DataTemplate RepositoryTemplate
{
get;
set;
}
public Style RepositoryItemStyle
{
get;
set;
}
}
Nigel's answer is great. I just added some attached properties to the WinRT XAML Toolkit that should make it simpler to do if you are populating your GridView using the ItemsSource property binding.
For me the usual way to modify the GridViewItem properties then was using GridView.ItemContainerStyle property. Using that method you would need to specify the IsEnabled property using a style and style setters don't support bindings in WinRT. Using the ItemContainerStyleSelector might be one way, but it requires defining a custom class.
I have created a GridViewItemExtensions class with an IsEnabled property that you can set on any control in your GridView.ItemTemplate like this:
xmlns:xyzc="using:Xyzzer.WinRT.Controls"
xyzc:GridViewItemExtensions.IsEnabled="{Binding IsEnabled}"
The property has a behavior of finding the GridViewItem in its ancestors visual tree and keeping its IsEnabled value synchronized to the GridViewItemExtensions.IsEnabled value set on its descendant.
Then as Nigel said - you still need to extract the template from a GridViewItem and modify it so the disabled items don't look out of place.
I have created a class that contains a property of type ObservableCollection. I am trying to create an instance of the class in XAML and fill this property with members. I keep getting an exception that class T can not be converted to ObservableCollection, but this exception only occurs when I am trying to populate the list with elements that were declared as static resources.
Anybody has an idea why?
The code is as follows:
<ResourceDictionary
xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
xmlns:mseg="clr-namespace:SegApp.Model.DataEntities.Segments;assembly=SegApp.Model.Silverlight">
<mseg:Dot xKey="d1"/>
<mseg:Dot xKey="d2"/>
<mseg:Dot xKey="d3"/>
<mseg:Dot xKey="d4"/>
<mseg:Segment xKey="seg1">
<mseg:Segment.Dots>
<StaticResource ResourceKey="d1"/>
<StaticResource ResourceKey="d2"/>
<StaticResource ResourceKey="d3"/>
<StaticResource ResourceKey="d4"/>
</mseg:Segment.Dots>
</mseg:Segment>
</ResourceDictionary>
The Class definition is:
public class Segment : Part
{
public ObservableCollection<Dot> Dots { get; set; }
public Segment()
{
Dots = new ObservableCollection<Dot>();
}
}
And the exception says:
"
Object of type bla.bla.bla.Dot can not
be converted to type
System.Collections.ObjectModel.ObservableCollection'1[bla.bla.bla.Dot]
"
Any ideas?
As is your code, each element of the collection must be a Dot, not a resource...
Each entry of the list in your xaml code must be something like
or perhaps try
somevalue
or
{staticResource xxx }
But there is still a problem. The 1st syntax is ok, the second can work if there is a simple content for Dot, but the 3rd can't run : tag means "create an instance of Dot". And a StaticResource means "create an instance of.. and give it a key".
So last syntax will certainly not work cause you can replace the instance created by the tag with the instance coming from the resource...
But give it a try. The main problem in your code is than you're trying to feel a collection of Dot with Resource, that can't work and the compiler is not ok.. try using tag to create entry. And then play a bit to see if you can refer the resources somewhere in these tags..
In order to use collections XAML syntax change your property and remove it's setter:
public class Segment : DependencyObject
{
private readonly ObservableCollection<Dot> _dots = new ObservableCollection<Dot>();
public ObservableCollection<Dot> Dots
{
get { return _dots; }
}
}