I would like to have a few Content Pages , which I add in my MainPage class. I use SetLayout function to do that, which parameter is ContentPage. How to dock a ContentPage to my ContentPage( MainPage) as children please?
My MainPage xaml:
<ContentPage xmlns="http://xamarin.com/schemas/2014/forms"
xmlns:x="http://schemas.microsoft.com/winfx/2009/xaml"
xmlns:local="clr-namespace:MyApp.MainPage"
x:Class="MyApp;assembly=App"
BackgroundColor="White">
<StackLayout x:Name="Form">
</StackLayout>
And SetLayout function in MainPage.cs
private void SetLayout(ContentPage page)
{
if (LastControl != null)
{
LastControl.IsEnabled = false;
Form.Children.Remove(LastControl);
Form.Children.Add(page);
}
else
{
Form.Children.Add(page);
}
page.IsVisible = true;
LastControl = page;
}
In function above I have error on Form.Children.Add, because this wants contentview, not contentpage.
I dont want to change my ContentPage to ContentView, because I want to have working BackButton.
Any idea? Thanks
Related
I have a simple project using Community Toolkit Mvvm tool and a collectionview. The issue is that the SelectionChangeCommand of the CollectionView doesn´t fired when I select an element of the collection. I created this project because on another more complex project the error is that it can't find the binding command on the viewmodel. I know that the connection between the view and viewmodel is working because the collectionview is filling with elements on the viewmodel and also I am able to change the visibility of the border through the binded property.
Sample project: https://github.com/luis95gr/MvvmError.App
Code
LoginPage (first page with collectionview)
<ContentPage xmlns="http://schemas.microsoft.com/dotnet/2021/maui"
xmlns:x="http://schemas.microsoft.com/winfx/2009/xaml"
x:Class="MvvmError.Views.LoginPage"
xmlns:models="clr-namespace:MvvmError.Models"
Title="LoginPage">
<RefreshView VerticalOptions="FillAndExpand">
<Border BackgroundColor="Red" IsVisible="{Binding Visible}" Stroke="Red" HorizontalOptions="FillAndExpand" Padding="0,0" Margin="0,0,0,0" VerticalOptions="FillAndExpand">
<Border.StrokeShape>
<RoundRectangle CornerRadius="40,0,0,0" />
</Border.StrokeShape>
<CollectionView Background="Transparent" ItemsSource="{Binding Messages}" SelectionMode="Single" SelectedItem="{Binding MessageSelected}" SelectionChangedCommand="{Binding MessageSelectedCommand}">
<CollectionView.ItemTemplate>
<DataTemplate x:DataType="models:MessagesMessages">
<Grid RowDefinitions="100*" ColumnDefinitions="100*">
<Label Grid.Row="0" Text="{Binding Asunto}" />
</Grid>
</DataTemplate>
</CollectionView.ItemTemplate>
</CollectionView>
</Border>
</RefreshView>
LoginPageViewModel
public partial class LoginPageViewModel : ObservableObject
{
[ObservableProperty]
private MessagesMessages messageSelected;
[ObservableProperty]
private bool visible;
public ObservableCollection<MessagesMessages> Messages { get; } = new();
public LoginPageViewModel()
{
Visible = true;
GetMessages();
}
[RelayCommand]
async void MessageSelectedCommand()
{
var snackbar = Snackbar.Make("Hola");
await snackbar.Show();
}
private void GetMessages()
{
Messages.Add(new MessagesMessages
{
Asunto = "Hola"
});
Messages.Add(new MessagesMessages
{
Asunto = "Hola1"
});
Messages.Add(new MessagesMessages
{
Asunto = "Hola2"
});
Messages.Add(new MessagesMessages
{
Asunto = "Hola3"
});
}
}
LoginPage.xaml.cs
public partial class LoginPage : ContentPage
{
public LoginPage(LoginPageViewModel loginPageViewModel)
{
InitializeComponent();
BindingContext= loginPageViewModel;
}
}
MauiProgram.cs
builder.Services.AddTransient<LoginPage>();
builder.Services.AddSingleton<ViewModels.LoginPageViewModel>();
you are not following the naming convention
The name of the generated command will be created based on the method
name. The generator will use the method name and append "Command" at
the end, and it will strip the "On" prefix, if present. Additionally,
for asynchronous methods, the "Async" suffix is also stripped before
"Command" is appeneded.
to generate a command named MessageSelectedCommand your method should look like
[RelayCommand]
async void MessageSelected()
I have implemented Tabbedpage using ViewModel but my ViewModel constructor call 4 times because I create 4 tabs, I also used prism for ViewModel binding.
Below is a design file
<?xml version="1.0" encoding="UTF-8"?>
<TabbedPage xmlns="http://xamarin.com/schemas/2014/forms"
xmlns:x="http://schemas.microsoft.com/winfx/2009/xaml"
xmlns:prism="clr-namespace:Prism.Mvvm;assembly=Prism.Forms"
xmlns:material="clr-namespace:XF.Material.Forms.UI;assembly=XF.Material"
xmlns:ffimageloading="clr-namespace:FFImageLoading.Forms;assembly=FFImageLoading.Forms"
xmlns:ffTransformations="clr-namespace:FFImageLoading.Transformations;assembly=FFImageLoading.Transformations"
prism:ViewModelLocator.AutowireViewModel="True"
xmlns:ios="clr-namespace:Xamarin.Forms.PlatformConfiguration.iOSSpecific;assembly=Xamarin.Forms.Core"
xmlns:extended="clr-namespace:Xamarin.Forms.Extended;assembly=Xamarin.Forms.Extended.InfiniteScrolling"
xmlns:customcontrols="clr-namespace:QuranicQuizzes.CustomControls"
xmlns:local="clr-namespace:QuranicQuizzes.Views" NavigationPage.HasNavigationBar="True"
x:Class="QuranicQuizzes.Views.DashboardPage">
<NavigationPage.TitleView>
<StackLayout Orientation="Horizontal" HorizontalOptions="FillAndExpand">
<Label Text="Dashboard" TextColor="White" HorizontalTextAlignment="Center" HorizontalOptions="CenterAndExpand" VerticalTextAlignment="Center" FontFamily="{StaticResource QuranFontBold}" FontSize="Medium" />
<StackLayout Orientation="Horizontal">
<material:MaterialMenuButton x:Name="Menus" ButtonType="Text" Image="list" TintColor="White" BackgroundColor="Transparent" CornerRadius="24" Choices="{Binding Actions}" MenuSelected="MaterialMenuButton_MenuSelected" />
</StackLayout>
</StackLayout>
</NavigationPage.TitleView>
<local:HomeTabPage/>
<local:QuizzesTabPage/>
<local:LiveGameTabPage/>
<local:AssignmentTabPage/>
</TabbedPage>
Below is my code
public partial class DashboardPage : TabbedPage
{
private DashboardPageViewModel vm;
public DashboardPage()
{
try
{
InitializeComponent();
vm = BindingContext as DashboardPageViewModel;
}
catch (Exception ex)
{
}
}
}
Below is my ViewModel
public class DashboardPageViewModel : ViewModelBase
{
INavigationService _navigationService;
IClientAPI _clientAPI;
Dashboards dashboard;
public DashboardPageViewModel(INavigationService navigationService, IClientAPI clientAPI) : base(navigationService)
{
_navigationService = navigationService;
_clientAPI = clientAPI;
if (CrossConnectivity.Current.IsConnected)
{
var StartDate = DateTime.Now.AddDays(-7).ToString("yyyy-MM-dd");
var Enddate = DateTime.Now.ToString("yyyy-MM-dd");
if (dashboard == null)
{
dashboard = new Dashboards();
getDashboardData(StartDate, Enddate);
}
}
}
}
I see what you're trying to do. You want to initialise your vm instance so that you can access you vm from your view.
Instead of doing this:
vm = BindingContext as DashboardPageViewModel;
what we can do is change the type of the existing BindingContext property by doing this:
public partial class DashboardPage
{
new DashboardPageViewModel BindingContext
{
get => (DashboardPageViewModel) base.BindingContext;
set => base.BindingContext = value;
}
public DashboardPage()
{
InitializeComponent();
}
}
now you can just access BindingContext.DoSomething because its type is now DashboardPageViewModel.
Now that's sorted out, your viewmodel should not be being called 4 times! Something is wrong here. Here is a checklist of things to do that may be causing the constructor being called 4 times as not a lot more info was provided.
Try removing <NavigationPage.TitleView> segment.
Make sure you are navigating to DashboardPage.
Make sure that each individual TabbedPage has it's own viewmodel.
Try removing prism:ViewModelLocator.AutowireViewModel="True"and manually adding the viewmodel to the TabbedPage.
Finally constructors should be able to run very fast and should only be used for assigning variables or instantiation or very quick operations. What you could maybe do is separate the code in your VM:
public class DashboardPageViewModel : ViewModelBase
{
IClientAPI _clientAPI;
Dashboards dashboard;
public DashboardPageViewModel(INavigationService navigationService, IClientAPI clientAPI) : base(navigationService)
{
_clientAPI = clientAPI;
}
public void Init()
{
if (CrossConnectivity.Current.IsConnected)
{
var StartDate = DateTime.Now.AddDays(-7).ToString("yyyy-MM-dd");
var Enddate = DateTime.Now.ToString("yyyy-MM-dd");
if (dashboard == null)
{
dashboard = new Dashboards();
getDashboardData(StartDate, Enddate);
}
}
}
}
and then in your view you could add this method:
protected override void OnBindingContextChanged()
{
base.OnBindingContextChanged();
if(BindingContext == null)
{
return;
}
BindingContext.Init();
}
I hope this really helps you.
NB: All this code was written on the fly and never compiled, there may be some errors.
I'm trying to implement TapGestureRecognizer which will be called in ViewModel (xaml.cs) not in View class...
Here is sample code in xaml file: (IrrigNetPage.xaml)
<ContentPage xmlns="http://xamarin.com/schemas/2014/forms"
xmlns:x="http://schemas.microsoft.com/winfx/2009/xaml"
xmlns:i18n="clr-namespace:agroNet.AppResource;assembly=agroNet"
xmlns:viewModels="clr-namespace:agroNet.ViewModel"
x:Class="agroNet.View.IrrigNetPage"
BackgroundColor="#EBEBEB">
<Grid>
<Grid.GestureRecognizers>
<TapGestureRecognizer Tapped="HideListOnTap"/>
</Grid.GestureRecognizers>
</Grid>
I implemented HideListOnTap in xaml.cs page (view) like this: (IrrigNetPage.xaml.cs)
int visibility = 1;
private void HideListOnTap(object sender, EventArgs e)
{
visibility++;
if ((visibility % 2) == 0)
{
IrrigList.IsVisible = false;
}
else
{
IrrigList.IsVisible = true;
}
}
It's working fine, but how to do the same thing usin ViewModel?
(How to bind Gesture recognizer from (IrrigNetPage.xaml) with HideListOnTap in IrrigNetViewModel )
Use a Command whenever you want to handle some event in the ViewModel. Without passing any arguments the code would look like as follows
<!-- in IrrigNetPage.xaml -->
<TapGestureRecognizer Command="{Binding HideListOnTapCommand}"/>
And in the ViewModel IrrigNetPageViewModel.cs
public ICommand HideListOnTapCommand { get; }
public IrrigNetPageViewModel()
{
HideListOnTapCommand = new Command(HideListOnTap);
// if HideListOnTap is async create your command like this
// HideListOnTapCommand = new Command(async() => await HideListOnTap());
}
private void HideListOnTap()
{
// do something
}
I'm trying to create a compound view component in Xamarin Forms called FormElement which is composed of two labels and an Entry:
<?xml version="1.0" encoding="UTF-8"?>
<StackLayout xmlns="http://xamarin.com/schemas/2014/forms"
xmlns:x="http://schemas.microsoft.com/winfx/2009/xaml"
xmlns:custom="clr-namespace:Mynamespace;assembly=Mynamespace"
x:Class="Mynamespace.Components.FormEntry">
<StackLayout Orientation="Horizontal">
<Label x:Name="formRequiredStar"
IsVisible="{Binding IsRequired}"
Text="*" TextColor="Red"
FontSize="15"
FontAttributes="Bold"
Margin="-12,0,0,0"
HorizontalOptions="Start" />
<Label x:Name="formLabel"
HorizontalOptions="Start"
Text="{Binding LabelText}"
TextColor="{Binding LabelTextColor}"
FontSize="{Binding LabelTextFontSize}"
FontAttributes="{Binding LabelTextFontStyle}" />
</StackLayout>
<Frame BorderColor="Black"
CornerRadius="7"
Padding="5,0"
Margin="0,-3,0,0"
HasShadow="false">
<Entry x:Name="mainEntry"
Keyboard="{Binding KeybdType}"
Placeholder="{Binding EntryPlaceHolder}"
TextColor="Black"
FontSize="Default"
HeightRequest="{Binding EntryHeight}" />
</Frame>
</StackLayout>
Next, I want to switch focus from the Entry to a "next" element when the user taps the DONE button, so I do:
namespace Mynamespace.Components
{
public partial class FormEntry : StackLayout
{
public VisualElement NextFocus
{
get { return (VisualElement)GetValue(NextFocusProperty); }
set { SetValue(NextFocusProperty, value); }
}
public static readonly BindableProperty NextFocusProperty =
BindableProperty.Create(nameof(NextFocus),
typeof(VisualElement),
typeof(FormEntry),
null,
Xamarin.Forms.BindingMode.OneWay);
public FormEntry()
{
InitializeComponent();
BindingContext = this;
mainEntry.Completed += (s, e) =>
{
if (NextFocus != null)
{
NextFocus.Focus();
}
};
}
}
}
Next, in order for a FormEntry to be the target of NextFocus, I tried adding
this.Focused += (s,e) => { mainEntry.Focus(); };
to the constructor, but the handler is never called, and I also tried overriding
public new void Focus() {
mainEntry.Focus();
}
but this method is never called. Layout classes are descended from VisualElement so they should inherit Focused. Is there something about Layout objects that I'm missing? I could understand that Layout objects aren't usually the target of focus, but the event handler is supposedly there so I ought to be able to use it.
Here's an example of how I utilize the FormEntry on a login screen:
<!-- Email -->
<controls:FormEntry x:Name="usernameEntry"
Margin="25,40,25,0"
IsRequired="true"
EntryHeight="40"
KeybdType="Email"
NextFocus="{x:Reference passwordEntry}"
LabelText="{il8n:Translate Emailorusername}"
EntryPlaceHolder="{il8n:Translate EnterUsername}">
</controls:FormEntry>
<!-- Password -->
<controls:FormEntry x:Name="passwordEntry"
Margin="25,0,25,0"
IsRequired="true"
EntryHeight="40"
LabelText="{il8n:Translate Password}"
EntryPlaceHolder="{il8n:Translate EnterPassword}" />
I think you have get the nextfocus element, you can get mainEntry from nextfocus, like this:
public FormEntry ()
{
InitializeComponent ();
BindingContext = this;
mainEntry.Completed += (s, e) =>
{
if (NextFocus != null)
{
FormEntry formentry = (FormEntry)NextFocus;
Entry entry = formentry.mainEntry;
entry.Focus();
}
};
}
Then you can find you will get focus.
i got some troubles with using the PageRenderer.
MainPage.xml
<ContentPage xmlns="http://xamarin.com/schemas/2014/forms"
xmlns:x="http://schemas.microsoft.com/winfx/2009/xaml"
x:Class="abc.CustomView">
<ContentPage.Content>
<StackLayout>
<Button Text="scann" Clicked="BtnScannClicked"></Button>
</StackLayout>
</ContentPage.Content>
MainPage.cs
async void BtnScannClicked(object sender, EventArgs e)
{
await Navigation.PushAsync(new CustomView());
}
CustomView.Xaml
<ContentPage xmlns="http://xamarin.com/schemas/2014/forms"
xmlns:x="http://schemas.microsoft.com/winfx/2009/xaml"
x:Class="abc.CustomView">
<ContentPage.Content>
</ContentPage.Content>
</ContentPage>
CustomView.cs
[XamlCompilation(XamlCompilationOptions.Compile)]
public partial class CustomView : ContentPage
{
public CustomView ()
{
InitializeComponent ();
}
}
DemoPage.cs (which is my CustomRenderer)
[assembly: ExportRenderer(typeof(CustomView), typeof(DemoPage))]
namespace abc.UWP
{
class DemoPage: PageRenderer
{
Page page;
Application app;
protected override void OnElementChanged(ElementChangedEventArgs<Xamarin.Forms.Page> e)
{
base.OnElementChanged(e);
if (e.OldElement != null || Element == null)
{
return;
}
try
{
app = Application.Current;
SetupUserInterface();
this.Children.Add(page);
}
catch (Exception ex)
{
Debug.WriteLine(#" ERROR: ", ex.Message);
}
}
void SetupUserInterface()
{
var stackPanel = new StackPanel();
page = new Page();
page.Content = stackPanel;
}
}
}
There is always a
Exception thrown: 'System.InvalidOperationException' in Xamarin.Forms.Platform.UAP.dll
error during the build.
But I guess this is not really a problem with the PageRenderer. Seems that this appears during the ClickEvent.
There is always a Exception thrown: 'System.InvalidOperationException' in Xamarin.Forms.Platform.UAP.dll error during the build.
The problem is that you have not add the MainPage to NavigationPage.
The PushAsync method is not supported globally on Windows. You could add the the following code to the app.xaml.cs file to solve the issue.
public App()
{
InitializeComponent();
var RootNav = new NavigationPage(new MainPage());
MainPage = RootNav;
}
PushModalAsync - Push a page into a modal context. This will create a new, independent, Navigation context within the application. The modal that is created can be dismissed with a hardware back button; there appears to no way to stop this functionality.
So the PushModalAsync method does not depend on NavigationPage, it will work in your current scenario.
Put my application is always crashing (has exit code -1) after the navigation to DemoPage.cs. The Implementation should be ok, or not?
I have found that you have not implemented ArrangeOverride method in your PageRenderer. And you will not see the content of page.
protected override Size ArrangeOverride(Size finalSize)
{
page.Arrange(new Windows.Foundation.Rect(0, 0, finalSize.Width, finalSize.Height));
return finalSize;
}