I'm extending a control to be able to reuse it across my current Xamarin project. As part of this control, I need to create a DataTemplate programmatically. I have this part figured out and it works ok.
The DataTemplate has a Label in it. I need to bind the Label's BindingContext property to {Binding Source}. I need to bind the Label's Text property to {Binding Path=Name}.
This works in XAML, but I don't want to have to copy it to a million different places in the code base.
<dxGrid:TemplateColumn FieldName="MyPropertyName"
Caption="MyColumn">
<dxGrid:TemplateColumn.DisplayTemplate>
<DataTemplate>
<Label BindingContext="{Binding Source}"
Text="{Binding Source, Path=MyPropertyName}" />
</DataTemplate>
</dxGrid:TemplateColumn.DisplayTemplate>
My extended control looks like this right now:
public class MyColumn : TemplateColumn
{
public MyColumn()
{
DataTemplate displayTemplate = new DataTemplate(() =>
{
BindingBase textBinding = new Binding(FieldName);
Label label = new Label();
// TODO: Bind BindingContextProperty to {Binding Source}
//label.SetBinding(BindingContextProperty, binding);
label.SetBinding(Label.TextProperty, textBinding);
return new ViewCell
{
View = label
};
});
DisplayTemplate = displayTemplate;
}
}
I'm getting hung up in the binding because I'm not sure how to do the equivalent of {Binding Source} in code. Any help would be appreciated.
#Eugene - Thanks for the response. Unfortunately this does not work and binding to "Source" like that throws a Null Reference Exception. I made another pass at it this morning and got it working this way:
public MyColumn()
{
DataTemplate displayTemplate = new DataTemplate(() =>
{
Grid grid = new Grid();
grid.SetBinding(Grid.BindingContextProperty, "Source");
Label label = new Label();
label.SetBinding(Label.TextProperty,FieldName);
grid.Children.Add(label);
return grid;
});
this.DisplayTemplate = displayTemplate;
}
It's simple, use name of property
label.SetBinding(BindingContextProperty, "Source");
Related
I have a Xamarin.Forms page written in .xaml On iOS platform only I am trying to wrap the content of the page in ScrollView to help fix resizing issue when keyboard is shown.
The page looks something like this:
<base:mypagebase...>
<ContentPage.Resources>
...
</ContentPage.Resources>
<ContentPage.Content>
<RelativeLayout x:Name="ViewContentLayout" VerticalOptions="FillAndExpand">
....
</RelativeLayou>
</ContentPage.Content>
</base:mypagebase>
I am trying in the constructor of my mpage.xaml.cs after InitializeComponent() to wrap my RelativeLayout in ScrollView
Something like this:
if (Device.RuntimePlatform == Device.iOS)
{
var scroll = new ScrollView();
scroll.Orientation = ScrollOrientation.Vertical;
scroll.VerticalOptions = LayoutOptions.FillAndExpand;
scroll.Content = ViewContentLayout;
Content = scroll;
}
It passes through but throws exception later:
Object reference not set to an instance of an object
at Xamarin.Forms.RelativeLayout.OnSizeRequest (System.Double widthConstraint, System.Double heightConstraint) [0x00017] in RelativeLayout.cs:185
The order in which the properties are called matters, seems like the Content root had to be set first:
if (Device.RuntimePlatform == Device.iOS)
{
var viewContentLayout = ViewContentLayout;
var scroll = new ScrollView();
Content = scroll;
scroll.Content = viewContentLayout;
}
I'm trying to use a custom variable to name UI Elements in XAML in order to use them in my Xamarin code. How would I do that?
I know that I can use the tags
<Label x:Name="CallVariable" Text="This will appear"/>
and I can call the label from Xamarin using
Label foo = FindByName("CallVariable") as Label;
and mess with the text with the following
foo.Text == "This will appear"
which should return true.
I learned about binding, and so I tried to use this in my variables.
<Label x:Name={Binding Name}/>
Label bar = FindByName(emp.training[i] as Label);
Unfortunately, every time I run it, I'm receiving the error:
System.NullReferenceException: Object reference not set to an instance of an object.
I remembered to set the BindingContext. And in case it's important, this is all happening within a list view.
Is x:Name a bindable object? Or is there another method I should be using? Maybe a way to call an object based on its label, or something?
My current task is as follows:
I have a list of people's information. Name, Age, Gender, Email, Location, and a few other pieces of information. I'm trying to get someone to search for certain types of people, have it return a list of everyone in a ListView, and have the person be able to select as many as they want. I did this using a button that adds the person to a list (or removes them from the list if they're already on). If the user chooses to, they should be able to also click "Select All" to add everyone. I've got the individual adding down, I just need to somehow select all of them.
You can't access the label with a listView by x:Name in code behind. Instead of access the label in the listView, you can bind the property of label in code behind. For example:
<ListView x:Name="testListView">
<ListView.ItemTemplate>
<DataTemplate>
<ViewCell>
<StackLayout>
<Label Text="{Binding Name}" />
<Label Text="{Binding Desc}" />
</StackLayout>
</ViewCell>
</DataTemplate>
</ListView.ItemTemplate>
</ListView>
And in code behind, it should be:
public partial class MainPage : ContentPage
{
ObservableCollection<testViewModel> myModels = new ObservableCollection<testViewModel>();
testViewModel model;
public MainPage()
{
InitializeComponent();
testListView.ItemsSource = myModels;
myModels.Add(new testViewModel { Name = "age" });
myModels.Add(new testViewModel { Name = "gender" });
myModels.Add(new testViewModel { Name = "name" });
}
}
class testViewModel
{
public string Name { get; set; }
public string Desc { get; set; }
}
Next time you want to update the text of label:
public void test() {
//Get the model you want to change
model.Desc = "This will appear";
}
I've got the individual adding down, I just need to somehow select
all of them.
I don't know how you implement the individual adding down, share the code and maybe I can give you some suggestions.
Hi I have a xaml app that has one particular color used in many places on a page. I want to programmatically change the value of this color. I don't want to have to update every object's color individually. I have tried this:
<Grid
Background="{Binding GalleryViewBrush, Mode=TwoWay}"
Grid.Row="0"
Grid.Column="0">
Then in codebehind:
public Brush GalleryViewBrush { get; set; }
GalleryViewBrush = new SolidColorBrush(Colors.Red);
But the color never works. I have tried xbind too but no luck
thanks
Your view model needs to implement INotifyPropertyChanged, and then fire the PropertyChanged event when your brush property changes. Conventionally that's done in the setter for the property.
private Brush _myBrush;
public MyBrush {
get { return _myBrush; }
set {
_myBrush = value;
PropertyChanged?.Invoke(this, new PropertyChangedEventArgs(nameof(MyBrush));
}
}
If your get/set for GalleryViewBrush in your question is what's actually in the code sample in your question, that's likely to be the issue.
Mind typos in my code sample above, I'm hammered ATM.
I ran into a weird problem working with the Windows Phone 8 pivot control.
Apparently, when the Pivot is bound to a list of models and the HeaderTemplate is used for binding to one of the model's properties, changing the property during runtime causes layout problem in the headers.
Here is the sample code.
Create a simple model class.
public class MyModel: INotifyPropertyChanged
{
private string _displayName;
public event PropertyChangedEventHandler PropertyChanged;
public string DisplayName
{
get
{
return _displayName;
}
set
{
_displayName = value;
if(PropertyChanged != null)
{
PropertyChanged(this, new PropertyChangedEventArgs("DisplayName"));
}
}
}
}
Then initialize the model list (could occur in the ViewModel, or page's code)
Items = new List<MyModel>
{
new MyModel { DisplayName = "model 1" },
new MyModel { DisplayName = "model 2" },
}
Connecting the list of models to the pivot control
<phone:Pivot ItemsSource="{Binding Items}" DisplayMemberPath="DisplayName">
<phone:Pivot.HeaderTemplate>
<DataTemplate>
<TextBlock Text="{Binding DisplayName}" />
</DataTemplate>
</phone:Pivot.HeaderTemplate>
</phone:Pivot>
So now we have 2 pivot items and the headers are displayed correctly. Now we change DisplayName property of the first item during app runtime (say following a button click) and assign a longer string value:
Items[0].DisplayName = "Some other header";
This causes the headers to overlap.
Any thoughts?
Elad
if you set displayName property to "Some other header" at first time, and then change the value to "model 2", normal display. So, in my opinion, this problem was caused by the pivot header width property(in your code,the textblock's width). When the pivot was loaded, every header had fixed width, and at this time, you changed the header display name to a longger value, the pivot will not be display correctly.
I want To access named controls inside listview datatemplet i followed this: How to Access a Named Control Inside a XAML DataTemplate (using CSharp
itemlistview.ItemsSource=new List<MyObject>();
foreach (var item in itemListView.Items)
{
var _Container = itemListView.ItemContainerGenerator
.ContainerFromItem(item);
var _Children = AllChildren(_Container);
var _FirstName = _Children.OfType<StackPanel>()
.First(x => x.Name.Equals("subjectListItem"));
_FirstName.Visibility =
Visibility.Collapsed;
}
But the problem in var item in itemListView.Items it retruns the MyObject which i passed to listview ItemsSource Not the controles inside the datatemplete.
So How can I return The Controls ?
ItemContainerGenerator.ContainerFromItem(object) should return an instance of ListViewItem that contains the data of the item.
But, this practice is discourage in WPF/WinRT frameworks. The "right" way is to control the data and have the UI react to it.
Something like:
// in code
var list = new List<MyObject>();
foreach (var item in list)
{
item.IsSomethingVisible = false;
}
itemlistview.ItemsSource = list;
<!--in XAML-->
<StackPanel Visibility="{Binding IsSomethingVisible,
Converter={StaticResource BooleanToVisibilityConverter}}".../>
<!--The converter is defined in resources of some higher level-->
<BooleanToVisibilityConverter x:Key="BooleanToVisibilityConverter"/>