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Shell navbar with trailing edge text

Is there a way to put a "trailing edge" text on a Shell navbar like on this pic?
I'm refactoring a project to use Shell. Before, it was done by changing the toolbar item when the user taps monthly, weekly or daily on that specific page. But now, I'm using Shell with flyout and the tabs are from CommunityToolkit TabView so the "pages" on the tabs are no longer contant pages but content views.
If I add a toolbar it will appear on all views, not only on this specific view.
I would like to add a text at the final of the navbar only on that specific view and change it when the user taps the monthly, weekly or daily options.
This is Xamarin Forms project.
Thanks!

You can achieve it by ViewModel and TapGestureRecognizer.
ViewModel:
namespace Forms_Shell.ViewModels
{
public class Page1ViewModel : INotifyPropertyChanged
{
public ICommand TapCommand { get; }
string selection;
public string Selection
{
get => selection;
set
{
selection = value;
OnPropertyChanged(nameof(Selection));
}
}
public Page1ViewModel()
{
Selection = "Monthly";
TapCommand = new Command<string>(Show);
}
private void Show(string a)
{
Selection = a;
}
public event PropertyChangedEventHandler PropertyChanged;
void OnPropertyChanged(string propertyName)
{
PropertyChanged?.Invoke(this, new PropertyChangedEventArgs(propertyName));
}
}
}
I don't know the xaml code of the monthly, weekly or daily options, so I use label as an example to replace it. Add a TapGestureRecognizer attached to Label:
<ContentPage xmlns="http://xamarin.com/schemas/2014/forms"
xmlns:x="http://schemas.microsoft.com/winfx/2009/xaml"
xmlns:vm="clr-namespace:Forms_Shell.ViewModels"
x:Class="Forms_Shell.Views.Page1"
Title="Page1">
<ContentPage.BindingContext>
<vm:Page1ViewModel />
</ContentPage.BindingContext>
<ContentPage.ToolbarItems>
<ToolbarItem Text="{Binding Selection}"/>
</ContentPage.ToolbarItems>
<ContentPage.Content>
<StackLayout Orientation="Horizontal" Padding="50,20">
<Label x:Name="Monthly" Text="Monthly" HorizontalOptions="CenterAndExpand">
<Label.GestureRecognizers>
<TapGestureRecognizer CommandParameter="{Binding Source={Reference Monthly},Path=Text}"
Command="{Binding TapCommand}"/>
</Label.GestureRecognizers>
</Label>
<Label Text="Weekly" x:Name="Weekly" HorizontalOptions="CenterAndExpand">
<Label.GestureRecognizers>
<TapGestureRecognizer CommandParameter="{Binding Source={Reference Weekly},Path=Text}"
Command="{Binding TapCommand}"/>
</Label.GestureRecognizers>
</Label>
<Label Text="Daily" x:Name="Daily" HorizontalOptions="CenterAndExpand">
<Label.GestureRecognizers>
<TapGestureRecognizer CommandParameter="{Binding Source={Reference Daily},Path=Text}"
Command="{Binding TapCommand}"/>
</Label.GestureRecognizers>
</Label>
</StackLayout>
</ContentPage.Content>
</ContentPage>
Update:
<ContentPage
...
xmlns:local="clr-namespace:Forms_Shell.Views"
xmlns:vm="clr-namespace:Forms_Shell.ViewModels"
xmlns:xct="http://xamarin.com/schemas/2020/toolkit"
...>
<ContentPage.BindingContext>
<vm:Page1ViewModel />
</ContentPage.BindingContext>
<ContentPage.ToolbarItems>
<ToolbarItem Text="{Binding Selection}"/>
</ContentPage.ToolbarItems>
<ContentPage.Content>
<StackLayout Orientation="Horizontal" Padding="50,20">
<xct:TabView TabStripPlacement="Top"
TabStripBackgroundColor="Blue"
TabStripHeight="50">
<xct:TabViewItem Text="Monthly"
x:Name="Monthly"
TextColor="White" TextColorSelected="Yellow" FontSize="12">
<xct:TabViewItem.GestureRecognizers>
<TapGestureRecognizer CommandParameter="{Binding Source={Reference Monthly},Path=Text}"
Command="{Binding TapCommand}"/>
</xct:TabViewItem.GestureRecognizers>
<local:ContentView1/>
</xct:TabViewItem>
<xct:TabViewItem Text="Weekly"
x:Name="Weekly"
TextColor="White" TextColorSelected="Yellow" FontSize="12">
<xct:TabViewItem.GestureRecognizers>
<TapGestureRecognizer CommandParameter="{Binding Source={Reference Weekly},Path=Text}"
Command="{Binding TapCommand}"/>
</xct:TabViewItem.GestureRecognizers>
<local:ContentView1/>
</xct:TabViewItem>
<xct:TabViewItem Text="Daily"
x:Name="Daily"
TextColor="White" TextColorSelected="Yellow" FontSize="12">
<xct:TabViewItem.GestureRecognizers>
<TapGestureRecognizer CommandParameter="{Binding Source={Reference Daily},Path=Text}"
Command="{Binding TapCommand}"/>
</xct:TabViewItem.GestureRecognizers>
<local:ContentView1/>
</xct:TabViewItem>
</xct:TabView>
</StackLayout>
</ContentPage.Content>
</ContentPage>
AppShell.xaml:
<Shell
...
xmlns:local="clr-namespace:Forms_Shell.Views"
xmlns:xct="http://xamarin.com/schemas/2020/toolkit"
Title="Forms_Shell"
x:Class="Forms_Shell.AppShell">
<FlyoutItem Title="About" Icon="icon_about.png">
<ShellContent Route="AboutPage" ContentTemplate="{DataTemplate local:AboutPage}" />
</FlyoutItem>
<FlyoutItem Title="Browse" Icon="icon_feed.png">
<ShellContent Route="ItemsPage" ContentTemplate="{DataTemplate local:ItemsPage}" />
</FlyoutItem>
<FlyoutItem Title="Page1">
<ShellContent Route="Page1" ContentTemplate="{DataTemplate local:Page1}" />
</FlyoutItem>
</Shell>

Popmodal from overriden back button

I am having some issues having my back button properly pop my modal after a user acknowledged that they will lose their changes if they do so. I suppose the issue lies in how to properly await the async method within a method that cannot be async due to how it is coded.
In my code behind I have the following method:
protected override bool OnBackButtonPressed()
{
base.OnBackButtonPressed();
Task<bool> confirm = DisplayAlert("Are you sure?", "All unsaved changes will be lost", "I'm Sure", "Cancel");
confirm.ContinueWith(x =>
{
if(x.Result)
{
var task = Navigation.PopModalAsync();
task.Wait();
}
});
return true;
}
I can see that it does properly hit my breakpoint inside if the user has clicked "I'm Sure". However, after doing that the modal still remains on the page.
I call my modal using the following method (it is wrapped in a NavigationPage as I wanted to be able to leverage Toolbar items, if this is an anti pattern please let me know)
private async void EditSwipeItem_Invoked(object sender, EventArgs e)
{
var unitOfWork = container.Resolve<IUnitOfWork>();
var invoked = sender as SwipeItem;
var element = invoked.BindingContext as InventoryModel;
await Navigation.PushModalAsync(new NavigationPage(new AddEditInventoryList(true, "8dc9e483-1d63-4629-b386-680ad7c9a324", element.InventoryId, unitOfWork)));
}
The code for the backbutton is based off of what I wrote for the CancelToolBar_Clicked, and it works correctly (That is, the modal is popped after the user acknowledges the prompt).
private async void CancelToolBar_Clicked(object sender, EventArgs e)
{
bool confirm = await DisplayAlert("Are you sure?", "All unsaved changes will be lost", "I'm Sure", "Cancel");
if(confirm)
await Navigation.PopModalAsync();
}
Edit:
This is what my XAML looks like:
<?xml version="1.0" encoding="utf-8" ?>
<ContentPage xmlns="http://xamarin.com/schemas/2014/forms"
xmlns:x="http://schemas.microsoft.com/winfx/2009/xaml"
x:Class="Invenutory.Views.Inventory.AddEditInventoryList">
<ContentPage.ToolbarItems>
<ToolbarItem Text="Save"
Order="Primary"
Clicked="SaveToolBarItem_Clicked"
Priority="1"/>
<ToolbarItem Text="Cancel"
Order="Secondary"
Clicked="CancelToolBar_Clicked"
Priority="0"/>
</ContentPage.ToolbarItems>
<ContentPage.Content>
<StackLayout HorizontalOptions="FillAndExpand" VerticalOptions="FillAndExpand"
Padding="20">
<Frame HorizontalOptions="FillAndExpand"
VerticalOptions="Start"
Padding="20"
CornerRadius="8"
BorderColor="AliceBlue">
<StackLayout
HorizontalOptions="FillAndExpand"
VerticalOptions="StartAndExpand">
<StackLayout HorizontalOptions="FillAndExpand" VerticalOptions="StartAndExpand"
Orientation="Vertical">
<Label Text="Name: " HorizontalOptions="Start" VerticalOptions="Start" />
<Entry HorizontalOptions="FillAndExpand" VerticalOptions="Start" Text="{Binding Name, Mode=TwoWay}" IsSpellCheckEnabled="True" IsTextPredictionEnabled="True" />
</StackLayout>
<StackLayout HorizontalOptions="FillAndExpand" VerticalOptions="StartAndExpand"
Orientation="Vertical">
<Label Text="Description: " HorizontalOptions="StartAndExpand" VerticalOptions="Start"/>
<Editor HorizontalOptions="FillAndExpand" VerticalOptions="Start" Text="{Binding Description, Mode=TwoWay}" IsSpellCheckEnabled="True" IsTextPredictionEnabled="True" />
</StackLayout>
<StackLayout HorizontalOptions="FillAndExpand" VerticalOptions="StartAndExpand"
Orientation="Vertical">
<Label Text="Count: " HorizontalOptions="Start" VerticalOptions="Start"/>
<Entry Keyboard="Numeric" HorizontalOptions="FillAndExpand" VerticalOptions="Start" Text="{Binding Count, Mode=TwoWay}" />
</StackLayout>
</StackLayout>
</Frame>
<Frame HorizontalOptions="FillAndExpand" VerticalOptions="FillAndExpand" Padding="20" CornerRadius="8" BorderColor="AliceBlue">
<StackLayout HorizontalOptions="FillAndExpand" VerticalOptions="FillAndExpand">
<Image HorizontalOptions="FillAndExpand" VerticalOptions="Start" HeightRequest="150" Aspect="AspectFit" BackgroundColor="Gray" Source="{Binding CapturedPhoto}" />
<Button Text="Take Photo" HorizontalOptions="FillAndExpand" VerticalOptions="Start" Command="{Binding TakePhotoCommand, Mode=TwoWay}"/>
</StackLayout>
</Frame>
</StackLayout>
</ContentPage.Content>
</ContentPage>

I was able to solve this by updating my inner .ContinueWith to look as follows:
confirm.ContinueWith(x =>
{
if(x.Result)
{
MainThread.BeginInvokeOnMainThread(async () =>
{
await Navigation.PopModalAsync();
});
}
});

Binding in generic control is null

I have several generic buttons. Both title and the corresponding icon are displayed correctly, but the tap function does not work.
HomePage.xaml with the ScanningApp control
<?xml version="1.0" encoding="utf-8" ?>
<ContentPage xmlns="http://xamarin.com/schemas/2014/forms"
xmlns:x="http://schemas.microsoft.com/winfx/2009/xaml"
x:Class="primetals.ScannerApp.Views.HomePage"
xmlns:controls="clr-namespace:primetals.ScannerApp.Controls"
xmlns:resource="clr-namespace:primetals.ScannerApp"
xmlns:prism="clr-namespace:Prism.Mvvm;assembly=Prism.Forms"
prism:ViewModelLocator.AutowireViewModel="True"
BackgroundColor="White"
x:Name="self"
Title="{Binding Title}">
<ContentPage.Resources>
<ResourceDictionary>
<Style TargetType="controls:ScanningApp">
<Setter Property="WidthRequest" Value="220"></Setter>
<Setter Property="HeightRequest" Value="220"></Setter>
</Style>
</ResourceDictionary>
</ContentPage.Resources>
<Grid Margin="10">
<Grid.RowDefinitions>
<RowDefinition Height="3*"></RowDefinition>
<RowDefinition Height="3*"></RowDefinition>
<RowDefinition x:Name="backgroundImageRow" Height="4*"></RowDefinition>
</Grid.RowDefinitions>
<StackLayout Grid.Row="0" HorizontalOptions="CenterAndExpand" Margin="0,10,0,10">
<!-- Application Logo -->
<Image Source="icon_scannerapp.png" WidthRequest="96" HeightRequest="96"></Image>
<!-- Welcome Text -->
<Label Text="{x:Static resource:ApplicationResources.WelcomeMessageLine1}" FontSize="Large">
</Label>
<Label FontSize="Large">
<Label.FormattedText>
<FormattedString>
<Span Text="{x:Static resource:ApplicationResources.WelcomeMessageLine2}"></Span>
<Span Text="{x:Static resource:ApplicationResources.WelcomeMessageSpareParts}" FontAttributes="Bold" FontSize="Large"></Span>
<Span Text="{x:Static resource:ApplicationResources.WelcomeMessageOr}"></Span>
<Span Text="{x:Static resource:ApplicationResources.WelcomeMessageSensorData}" FontAttributes="Bold" FontSize="Large"></Span>
<Span Text="!"></Span>
</FormattedString>
</Label.FormattedText>
</Label>
</StackLayout>
<!-- Scanning Applications -->
<StackLayout Orientation="Horizontal" Grid.Row="1" BindableLayout.ItemsSource="{Binding Apps}" HorizontalOptions="Center" VerticalOptions="Start">
<BindableLayout.ItemTemplate>
<DataTemplate>
<controls:ScanningApp Margin="0,0,5,0"
ImageSource="{Binding ImageUrl}"
TapImageSource="{Binding TapImageUrl}"
Text="{Binding Title}"
TappedCommand="{Binding BindingContext.AppTappedCommand, Source={x:Reference self}}"
TappedCommandParameter="{Binding}">
</controls:ScanningApp>
</DataTemplate>
</BindableLayout.ItemTemplate>
</StackLayout>
<!-- Background Image -->
<Image x:Name="backgroundImage" Grid.Row="2" Source="background_scannerapp_PT.jpg" Aspect="AspectFit" HorizontalOptions="Fill" VerticalOptions="Fill"></Image>
</Grid>
</ContentPage>
HomepageViewModel.cs:
AppTappedCommand is set correctly
this.AppTappedCommand = new DelegateCommand<ScanApplication>((app) => OnGotoScanPage(app));
this.Title = ApplicationResources.ApplicationTitleCaption;
public async void OnGotoScanPage(ScanApplication app)
{
NavigationParameters parameters = new NavigationParameters();
parameters.Add(Constants.Parameters.App, app.AppId);
await this.NavigationService.NavigateAsync($"{nameof(ScanPage)}", parameters);
}
ScanningApp.xaml.cs:
After Clicking the button TappedCommand is null.
public static readonly BindableProperty TappedCommandProperty = BindableProperty.Create(nameof(TappedCommand), typeof(ICommand), typeof(ScanningApp), default(ICommand), Xamarin.Forms.BindingMode.OneWay);
public ICommand TappedCommand
{
get
{
return (ICommand)GetValue(TappedCommandProperty);
}
set
{
SetValue(TappedCommandProperty, value);
}
}
public static readonly BindableProperty TappedCommandParameterProperty = BindableProperty.Create(nameof(TappedCommandParameter), typeof(object), typeof(ScanningApp), null, Xamarin.Forms.BindingMode.OneWay);
public object TappedCommandParameter
{
get
{
return GetValue(TappedCommandParameterProperty);
}
set
{
SetValue(TappedCommandParameterProperty, value);
}
}
private bool OnExecuteTap()
{
img.Source = this.ImageSource;
if (this.TappedCommand != null && this.TappedCommand.CanExecute(this.TappedCommandParameter))
{
this.TappedCommand.Execute(this.TappedCommandParameter);
}
return false;
}
ScanningApp.xaml
<?xml version="1.0" encoding="utf-8" ?>
<ContentView 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"
prism:ViewModelLocator.AutowireViewModel="True"
x:Class="primetals.ScannerApp.Controls.ScanningApp"
x:Name="self">
<Grid Padding="1" BackgroundColor="{StaticResource PrimetalsLightGrayColor}">
<Grid>
<Grid.GestureRecognizers>
<TapGestureRecognizer Tapped="TapGestureRecognizer_Tapped"></TapGestureRecognizer>
</Grid.GestureRecognizers>
<Grid.RowDefinitions>
<RowDefinition Height="5*"></RowDefinition>
<RowDefinition Height="1*" ></RowDefinition>
</Grid.RowDefinitions>
<Image x:Name="img" Grid.Row="0" Source="{Binding ImageSource, Source={x:Reference self}}" Aspect="AspectFit" VerticalOptions="CenterAndExpand"
Margin="20"></Image>
<Label Grid.Row="1" Text="{Binding Text, Source={x:Reference self}}"
Margin="10,0,10,10"
FontSize="Medium" TextColor="{StaticResource PrimetalsAccentColor}"
VerticalTextAlignment="Center" HorizontalTextAlignment="Center"></Label>
</Grid>
</Grid>
</ContentView>
Originally this sourcecode worked (about one year ago) (but there may be problems with new packages in VS). I hope you can help me. Thanks a lot!
br

It seems that there should be a TapGestureRecognizer_Tapped event handler in ScanningApp.xaml.cs from your code.
<TapGestureRecognizer Tapped="TapGestureRecognizer_Tapped"></TapGestureRecognizer>
So you could do like :
private void TapGestureRecognizer_Tapped(object sender, EventArgs e)
{
img.Source = this.ImageSource;
if (this.TappedCommand != null && this.TappedCommand.CanExecute(this.TappedCommandParameter))
{
this.TappedCommand.Execute(this.TappedCommandParameter);
}
}

How to add control in stacklayout of contentview in contentpage?

I am using xamarin.forms. having two projects Android and IOS.
I have one ContentView page with following code
<ContentView.Content>
<StackLayout x:Name="slMain" Padding="1" BackgroundColor="#7ABA45">
<StackLayout VerticalOptions="FillAndExpand" Padding="0,0,20,0" HeightRequest="50" HorizontalOptions="FillAndExpand">
<Label x:Name="lblTitle" VerticalOptions="CenterAndExpand" />
</StackLayout>
<StackLayout x:Name="sl" IsVisible="False" BackgroundColor="White">
</StackLayout>
</StackLayout>
</ContentView.Content>
// In Behind code(.cs file)
public ExpandCollapseStackLayout()
{
InitializeComponent();
var tapGestureRecognizer = new TapGestureRecognizer();
tapGestureRecognizer.Tapped += (s, e) =>
{
sl.IsVisible = !sl.IsVisible;
};
lblTitle.GestureRecognizers.Add(tapGestureRecognizer);
slMain.GestureRecognizers.Add(tapGestureRecognizer);
}
public string Title
{
get
{
return lblTitle.Text;
}
set
{
lblTitle.Text = value;
}
}
I want to add controls in StackLayout named "sl" of contentview in ContentPage at design time.
I dont want to add at runtime
Please suggest me how can I add Control in Contentview stacklayout?

If you want to add controls in design time simply declare them in your XAML, example:
<StackLayout x:Name="sl" IsVisible="False" BackgroundColor="White">
<!-- Add here your controls -->
<Label ... />
<Button .. />
</StackLayout>
If you want to add controls at runtime, you need to do it using your code behind page in C#. Example:
void AddControl()
{
var btn = new Button();
sl.Children.Add(btn);
}

Code for ContentView:
<ContentView.Content>
<StackLayout x:Name="slMain" Padding="1" BackgroundColor="#7ABA45" >
<StackLayout VerticalOptions="FillAndExpand" Padding="0,0,10,0" HeightRequest="50" HorizontalOptions="FillAndExpand" Orientation="Horizontal">
<Label x:Name="lblTitle" VerticalOptions="CenterAndExpand" HorizontalOptions="FillAndExpand" Margin="10,0,0,0" TextColor="White" FontAttributes="Bold" />
<Label Text="{ x:Static local:GrialShapesFont.ArrowDown }" HorizontalOptions="End" VerticalOptions="CenterAndExpand" TextColor="White" Style="{ StaticResource FontIconBase }" FontSize="26" />
</StackLayout>
<Frame Padding="10" IsVisible="False" BackgroundColor="White" x:Name="ContentFrame" OutlineColor="Black" HasShadow="False">
</Frame>
</StackLayout>
</ContentView.Content>
CS Code for ContentView:
[ContentProperty("ContainerContent")]
public partial class ExpandCollapseStackLayout : ContentView
{
public ExpandCollapseStackLayout()
{
InitializeComponent();
var tapGestureRecognizer = new TapGestureRecognizer();
tapGestureRecognizer.Tapped += (s, e) =>
{
ContentFrame.IsVisible = !ContentFrame.IsVisible;
};
lblTitle.GestureRecognizers.Add(tapGestureRecognizer);
slMain.GestureRecognizers.Add(tapGestureRecognizer);
}
public View ContainerContent
{
get { return ContentFrame.Content; }
set { ContentFrame.Content = value; }
}
public string Title
{
get
{
return lblTitle.Text;
}
set
{
lblTitle.Text = value;
}
}
}
Add Control in ContentPage:
<control:ExpandCollapseStackLayout Title="Demo" Padding="0,10,0,0">
<control:ExpandCollapseStackLayout.ContainerContent >
<StackLayout>
<Label Text="Add Content Here"></Label>
</StackLayout>
</control:ExpandCollapseStackLayout.ContainerContent>
</control:ExpandCollapseStackLayout>

Picker not showing Items

Am new in xamarin forms,i have a picker and populated it with items but it can't display the items.here is my code.
Picker in Xaml
<StackLayout Margin="1">
<Picker x:Name="curr_picker" Title="select currency">
</Picker>
</StackLayout>
How i populated it in cs
curr_picker.Items.Add("UGX");
curr_picker.Items.Add("USD");
curr_picker.Items.Add("JPY");
Here is my full code
xaml
ContentPage xmlns="http://xamarin.com/schemas/2014/forms"
xmlns:x="http://schemas.microsoft.com/winfx/2009/xaml"
x:Class="FX2.ForexRates"
Title="Forex Rates"
>
<Grid>
<Grid.RowDefinitions>
<RowDefinition Height=".3*" />
<RowDefinition Height=".7*" />
</Grid.RowDefinitions>
<StackLayout Orientation="Vertical">
<!--Frame 1 -->
<Frame Margin="5" HasShadow="True" BackgroundColor="White" >
<Frame.OutlineColor>
<OnPlatform x:TypeArguments="Color" Android="Gray" iOS="#DCDCDC" />
</Frame.OutlineColor>
<StackLayout Orientation="Vertical">
<Image Source="searchbox.png" HorizontalOptions="EndAndExpand"/>
<Image Source="flag_uganda.png" HorizontalOptions="StartAndExpand"/>
</StackLayout>
</Frame>
<Frame Margin="5" HasShadow="True" BackgroundColor="White" >
<Frame.OutlineColor>
<OnPlatform x:TypeArguments="Color" Android="Gray" iOS="#DCDCDC" />
</Frame.OutlineColor>
<StackLayout Orientation="Vertical">
<Label Text="UGANDA" HorizontalOptions="Center" TextColor="#5dade2"/>
<Image Source="searchbox.png" HorizontalOptions="EndAndExpand"/>
<Label Text="Compare With" HorizontalOptions="Center" TextColor="#5dade2"/>
<StackLayout Margin="1">
<Picker x:Name="curr_picker" Title="select currency">
</Picker>
</StackLayout>
<Picker x:Name="option_picker" Title="BUY or SELL">
</Picker>
<Button Text="VIEW RATES" BackgroundColor="#0711a7" HorizontalOptions="FillAndExpand" TextColor="White" HeightRequest="65" Clicked="Button_Clicked"/>
</StackLayout>
</Frame>
</StackLayout>
</Grid>
</ContentPage>
cs
using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;
using Xamarin.Forms;
using Xamarin.Forms.Xaml;
namespace FX2
{
[XamlCompilation(XamlCompilationOptions.Compile)]
public partial class ForexRates : ContentPage
{
public ForexRates()
{
InitializeComponent();
curr_picker.Items.Add("UGX");
curr_picker.Items.Add("USD");
curr_picker.Items.Add("JPY");
option_picker.Items.Add("BUY");
option_picker.Items.Add("SELL");
}
private void Button_Clicked(object sender, EventArgs e)
{
//await Navigation.PushAsync(new MainActivity());
}
}
}

If you are using newest Xamarin.Forms, like version 2.5 or later, you probably should use ItemsSource instead of Items for data binding. In XAML it will look like this:
<Picker x:Name="picker">
<Picker.ItemsSource>
<x:Array Type="{x:Type x:String}">
<x:String>Baboon</x:String>
<x:String>Capuchin Monkey</x:String>
<x:String>Blue Monkey</x:String>
</x:Array>
</Picker.ItemsSource>
</Picker>
In CS like this:
var monkeyList = new List<string>();
monkeyList.Add("Baboon");
monkeyList.Add("Capuchin Monkey");
monkeyList.Add("Blue Monkey");
picker.ItemsSource = monkeyList;
Instead of simple string you can also use complex types, check more here:
https://developer.xamarin.com/guides/xamarin-forms/user-interface/picker/populating-itemssource/

From the docs:
However, a Picker doesn't show any data when it's first displayed. Instead, the value of its Title property is shown as a placeholder on the iOS and Android platforms:
When the Picker gains focus, its data is displayed and the user can select an item: