I've been working on a UWP app for quite some time. We recently decided to transition over to Xamarin so that we can easily support Android alongside UWP. I've had no issues setting up a PCL to use for our code base. Now I'm running into some nightmares when trying to rewrite our UI for Xamarin.Forms. I'm trying to accomplish something relatively simple and I must be doing something hilariously wrong, but, I cannot figure out what.
I want to display a listView. Here's the XAML:
<ContentPage.Content>
<StackLayout>
<Label Text="This is the bill page."
VerticalOptions="CenterAndExpand"
HorizontalOptions="CenterAndExpand" />
<ListView x:Name="lvBills"
ItemsSource="{Binding Bills}"
SelectedItem="{Binding SelectedBill}">
<ListView.ItemTemplate>
<DataTemplate>
<StackLayout Orientation="Horizontal">
<Label Text="{Binding Amount}"
TextColor="White"
VerticalOptions="CenterAndExpand"
HorizontalOptions="CenterAndExpand"/>
<Label Text="{Binding DueDate}"
VerticalOptions="CenterAndExpand"
HorizontalOptions="CenterAndExpand"
TextColor="White"/>
</StackLayout>
</DataTemplate>
</ListView.ItemTemplate>
</ListView>
</StackLayout>
</ContentPage.Content>
When I run it, the listView populates with each item in my observable collection. However, no text is actually displayed..even if I remove the bindings and use some placeholder text. Additionally, if I click on any item in the listView, this exception crashes the program.
System.InvalidCastException: Unable to cast object of type
'Xamarin.Forms.StackLayout' to type 'Xamarin.Forms.Cell'.
at Xamarin.Forms.Internals.TemplatedItemsList`2.ActivateContent(Int32 index,
Object item)
at Xamarin.Forms.Internals.TemplatedItemsList`2.CreateContent(Int32 index, O
Object item, Boolean insert)
at Xamarin.Forms.Internals.TemplatedItemsList`2.GetOrCreateContent(Int32
index, Object item)
at Xamarin.Forms.Internals.TemplatedItemsList`2.get_Item(Int32 index)
at Xamarin.Forms.L
I can't figure out any search that yields any meaningful results. I've tried some other things: Adding a binding for ItemSelected in the xaml. I've tried to wire up delegates in the xaml.cs But I cannot make any progress. So, what am I doing wrong?
You need a ViewCell inside a DataTemplate:
<ContentPage.Content>
<StackLayout>
<Label Text="This is the bill page."
VerticalOptions="CenterAndExpand"
HorizontalOptions="CenterAndExpand" />
<ListView x:Name="lvBills"
ItemsSource="{Binding Bills}"
SelectedItem="{Binding SelectedBill}">
<ListView.ItemTemplate>
<DataTemplate>
<ViewCell> <!-- <----- Add this -->
<StackLayout Orientation="Horizontal">
<Label Text="{Binding Amount}"
TextColor="White"
VerticalOptions="CenterAndExpand"
HorizontalOptions="CenterAndExpand"/>
<Label Text="{Binding DueDate}"
VerticalOptions="CenterAndExpand"
HorizontalOptions="CenterAndExpand"
TextColor="White"/>
</StackLayout>
</ViewCell>
</DataTemplate>
</ListView.ItemTemplate>
</ListView>
</StackLayout>
</ContentPage.Content>
Related
Im buildining a novel-manga app.
When i came to novels there was about 2000 chapthers and i need to render them all at once.
Im using a listview to render them but its to damnt slow.
I was wondering if there is a faster solution like a renderer or somthing i could build that will work faster.
Here is my current XAML
<ListView ItemsSource="{Binding Chapters}"
x:Name="grdChapters"
ItemSelected="GrdChapters_ItemSelected">
<ListView.ItemTemplate>
<DataTemplate>
<ViewCell>
<StackLayout Padding="5" HeightRequest="30">
<StackLayout Orientation="Horizontal">
<Label TextColor="Black" Text="{Binding Name}" VerticalOptions="Center" HorizontalOptions="StartAndExpand" Style="{StaticResource header}" FontAttributes="None" />
<Image Source="right.png" HorizontalOptions="End" IsVisible="{Binding Completed}" WidthRequest="16" HeightRequest="16" Aspect="AspectFit" />
</StackLayout>
<BoxView Style="{StaticResource lightLine}" />
</StackLayout>
</ViewCell>
</DataTemplate>
</ListView.ItemTemplate>
</ListView>
The RecycleElementAndDataTemplate should improve your performance, because even though you're not using any dynamic images, the datatamplate is the same for all of the items in the list and it'll get optimized.
If that doesn't help, I'd recommend using the glidex library for Xamarin.Android, it makes scrolling a lot smoother.
My issue is when I add in labels to my ListView they wont show.
I am binding the labels to objects inside "DummyClass". FirstName, LastName, RepId.
I have done plenty amount of research over this issue and have asked multiple people to help on this subject but nothingenter image description here seems to work.
<StackLayout>
<ListView x:Name="listView"
HeightRequest="100">
<ListView.ItemTemplate>
<DataTemplate>
<ViewCell>
<StackLayout>
<Label Text="Hello"
BackgroundColor="Red"
VerticalOptions="FillAndExpand"/>
<Label Text="Yes"
BackgroundColor="Red"
VerticalOptions="FillAndExpand"/>
<Label Text="Wooohooo"
BackgroundColor="Red"
VerticalOptions="FillAndExpand"/>
</StackLayout>
</ViewCell>
</DataTemplate>
</ListView.ItemTemplate>
</ListView>
</StackLayout>
I found out what my issue was. It was the ItemSource. My ItemSource was not defined correctly. Fixed all the issues I was having. Thank you all for helping!
I have a listview. This list view has 5 rows with two buttons namely A & B. When I tap on button A on a row, I want to change the image on A as well as B on the same row and vice-versa. I am able to individually tap and change the image on the same button but don't know how to change the image on the other button. Here is my listview:
<ListView x:Name="GroupedView" SeparatorColor="Transparent" GroupDisplayBinding="{Binding Title}" IsGroupingEnabled="true" HasUnevenRows="true" >
<ListView.GroupHeaderTemplate>
<DataTemplate>
<ViewCell>
<StackLayout Orientation="Horizontal" Padding="5" BackgroundColor="#E2F5F9">
<Label Text="{Binding Title}" TextColor="{StaticResource NavyBlue}" />
</StackLayout>
</ViewCell>
</DataTemplate>
</ListView.GroupHeaderTemplate>
<ListView.ItemTemplate>
<DataTemplate>
<ViewCell>
<StackLayout Orientation="Horizontal" Spacing="2" Padding="5">
<StackLayout VerticalOptions="FillAndExpand">
<Label Text="{Binding QuestionName}" />
</StackLayout>
<StackLayout IsVisible="{Binding ShowYesNo}" Spacing="15" Orientation="Horizontal" HorizontalOptions="End">
<Button ClassId="Yes" Clicked="ChoiceSelected" CommandParameter="{Binding question_id}" Image="{Binding YesChoiceImg}" />
<Button ClassId="No" Clicked="ChoiceSelected" CommandParameter="{Binding question_id}" Image="{Binding NoChoiceImg}" />
</StackLayout>
</StackLayout>
</ViewCell>
</DataTemplate>
</ListView.ItemTemplate>
</ListView>
I am then using the sender to identify the class ID and change the image of the button.
Should I be using a command? Should I be doing something else? Please help. Thanks
If you want to use the CommandParameter you should be using a Command. At the moment you're mixing 2 different ways to handle the click.
One thing to note though is that if you use a command you usually want to bind it to a Command that is defined on your ViewModel but since inside the DataTemplate your BindingContext is the ListView item instead of the ViewModel so you have to reference around that. Something like this should work:
<DataTemplate>
<ViewCell>
<StackLayout Orientation="Horizontal" Spacing="2" Padding="5">
<StackLayout VerticalOptions="FillAndExpand">
<Label Text="{Binding QuestionName}" />
</StackLayout>
<StackLayout IsVisible="{Binding ShowYesNo}" Spacing="15" Orientation="Horizontal" HorizontalOptions="End">
<Button ClassId="Yes" Command="{Binding Path=BindingContext.ButtonCommand, Source={x:Reference MyQuestionPage}}" CommandParameter="{Binding .} Image="{Binding YesChoiceImg}" />
<Button ClassId="No" Clicked="ChoiceSelected" CommandParameter="{Binding question_id}" Image="{Binding NoChoiceImg}" />
</StackLayout>
</StackLayout>
</ViewCell>
</DataTemplate>
Note here that you have to give your ContentPage an x:Name (so you can reference it and call the BindingContext on it). And the "{Binding .}" binds to the current list item. So no need to search for it on id you can just plug it into the command directly!
I don't know why, but when I tap any ListView item, the Button inside it's template loses the background color.
I use default ViewCell inside ListView. Is this a Xamarin.Forms bug?
I have this problem only on iOS.
<ListView x:Name="lv" Grid.Row="2" HasUnevenRows="true" BackgroundColor="White" ItemTapped="OnItemTapped">
<ListView.ItemTemplate>
<DataTemplate>
<ViewCell>
<StackLayout Padding="16" HorizontalOptions="FillAndExpand" VerticalOptions="FillAndExpand" BackgroundColor="{Binding .,Converter={StaticResource IndexColorConverter}">
<StackLayout VerticalOptions="Center">
<Label Text="{Binding Auditorium}" FontSize="18" TextColor="Black"/>
<ContentView Padding="0,-5,0,0">
<Label Text="{Binding Title}" FontSize="16" TextColor="Black"/>
</ContentView>
<StackLayout Orientation="Horizontal">
<Button WidthRequest="100" Text="{Binding ButtonOverviewText}" TextColor="White" BackgroundColor="{Binding ButtonColor}" CommandParameter="{Binding .}" Clicked="Handle_Clicked"/>
<Button WidthRequest="100" Text="{Binding ButtonOverviewText}" TextColor="White" BackgroundColor="{Binding ButtonColor}" CommandParameter="{Binding .}" Clicked="Handle_Clicked" />
</StackLayout>
</StackLayout>
<Label Text="{Binding Coordinator}" FontSize="14" TextColor="Gray"/>
</StackLayout>
</ViewCell>
</DataTemplate>
</ListView.ItemTemplate>
</ListView>
There was an old issue that I filed fora similar bug: https://bugzilla.xamarin.com/show_bug.cgi?id=27502.
However, the specific scenario you mention is expected behavior on iOS and happens in native (non-Xamarin.Forms) projects too. See the comment here. You might consider disabling the UITableViewCellSelectionStyle of your cells with UITableViewCellSelectionStyle.None. Here is an example of a cell renderer. You can set the cell.SelectionStyle here. This would stop the gray highlight of the cell. If you don't want that it could be a workaround to keep your button colors.
My workaround for this problem is the following.
<Grid>
<BoxView BackgroundColor="{Binding ButtonColor}"/>
<Button Text="{Binding ButtonOverviewText}" TextColor="White" BackgroundColor="Transparent" CommandParameter="{Binding .}" Clicked="Handle_Clicked"/>
</Grid>
<ListView x:Name="ListNewsLetter" AbsoluteLayout.LayoutFlags="All" AbsoluteLayout.LayoutBounds="0,0,1,1" SeparatorVisibility="Default" VerticalOptions="Fill" ItemTapped="ListNewsLetter_ItemTapped" HasUnevenRows="True">
<ListView.ItemTemplate>
<DataTemplate>
<ViewCell>
<ViewCell.View>
<StackLayout HorizontalOptions="Fill" VerticalOptions="Center" Padding="5">
<StackLayout Padding="1" BackgroundColor="#f15a23" HorizontalOptions="FillAndExpand" VerticalOptions="FillAndExpand">
<StackLayout x:Name="stkNewsLetter" VerticalOptions="Center" BackgroundColor="#f15a23" Orientation="Horizontal" HeightRequest="30" Padding="6,0,6,0">
<Label x:Name="lblName" Text="{Binding NewsHeadline}" HorizontalOptions="StartAndExpand" TextColor="White" VerticalTextAlignment="Center" FontSize="Small"/>
<Image x:Name="imgPlus_Minus" HeightRequest="20" WidthRequest="20" Source="ico_down_arrow2_right.png" HorizontalOptions="End" ClassId="{Binding TapId}">
<Image.GestureRecognizers>
<TapGestureRecognizer Tapped="img_Tapped" NumberOfTapsRequired="1" />
</Image.GestureRecognizers>
</Image>
</StackLayout>
<StackLayout x:Name="stkNewsLetterDetail" Orientation="Vertical" BackgroundColor="#ffffff" IsVisible="true" HorizontalOptions="FillAndExpand" Padding="6,0,6,0">
<Label x:Name="lblDate" Text="{Binding NewsDate}" HorizontalOptions="StartAndExpand" VerticalTextAlignment="Start" TextColor="#585858" FontSize="Small"/>
<Label x:Name="lblDetail" Text="{Binding NewsDetails}" HorizontalOptions="FillAndExpand" VerticalTextAlignment="Start" TextColor="#585858" FontSize="Small"/>
</StackLayout>
</StackLayout>
</StackLayout>
</ViewCell.View>
</ViewCell>
</DataTemplate>
</ListView.ItemTemplate>
</ListView>
As you see in code ListView having main two child named "stkNewsLetter" and "stkNewLetterDetail". First Stack having Image and I want to change visibility of second stack on Image tap event.
In windows phone It will possible to get UI elements of List view but In xamarin.forms how it is possible?
You should bind to the Visability property on the stackLayout in the same way you are binding the Text. If the stackLayout doesn't have a visibility property you may need to wrap it within another control that does.
The click should change a visibility property in you viewmodel which will get picked up by the binding mentioned above.
For those who came here to get the child elements through Name like me,here is the solution:
var selectedItem = //any item selected within listview through OnItemTapped
StackLayout child1 = selectedItem.FindByName<StackLayout>("stkNewsLetter");