Reinitializing MasterPage throws null exception on IOS - Xamarin forms
I have an MDPage which is a MasterDetailPage that calls the side menu list page as Master. A detail for this has been added with a new home page navigation page.
My code
public MDPage(){
Master = new SideMenuPage();
InitializeComponent();
masterPage.ListView.ItemSelected += OnItemSelected;
Detail = new NavigationPage(new HomePage())
{
BarBackgroundColor = Color.Black,
BarTextColor = Color.White,
};}
I have a requirement where the NavigationPage contains a bottom menu, so that when the bottom menu is clicked, the MDPage needs to be reinitialized to set a new navigation page of another page (like the AboutUs page). So I added a parameterized constructor for the MDPage and by clicking the bottom menu item, I call App.Current.MainPage = new MDPage("AboutUs")
.Below - this is a parameterized constructor.
public MDPage(string bottomMenuItem)
{
Master = new SideMenuPage();
InitializeComponent();
masterPage.ListView.ItemSelected += OnItemSelected;
if("AboutUs" == bottomMenuItem)
{
Detail = new NavigationPage(new AboutUs())
{
BarBackgroundColor = Color.Black,
BarTextColor = Color.White,
};
}}
Here, the MDPage constructor is called initially when I open the application. Then, from the side menu, I have the option to open the home page, which is added as a detail. Note that this HomePage contains a bottom submenu which is nothing more than an image. By choosing this, it must reinitialize the MDPage again. It works great here in Andorida. But on iOS this throws an exception. This prevents me from installing Master = new SideMenuPage();
. I found the reason for the error in trial and error, as this code will not throw an exception and it throws the iOS Main.cs file. Please help me.
MainPage - XAML
<?xml version="1.0" encoding="utf-8" ?>
<MasterDetailPage xmlns="http://xamarin.com/schemas/2014/forms"
xmlns:x="http://schemas.microsoft.com/winfx/2009/xaml"
xmlns:local="clr-namespace:ClubApp.Views;assembly=ClubApp"
x:Class="ClubApp.Views.MainPage">
<MasterDetailPage.Master>
<local:MasterPage x:Name="masterPage" />
</MasterDetailPage.Master>
<MasterDetailPage.Detail>
<NavigationPage>
<x:Arguments>
</x:Arguments>
</NavigationPage>
</MasterDetailPage.Detail>
</MasterDetailPage>
MainPage.xaml.cs
using System.Linq;using System.Text;using System.Threading.Tasks;using Xamarin.Forms;namespace Test.Views{
public partial class MainPage : MasterDetailPage
{
public MainPage()
{
Master = new MasterPage();
InitializeComponent();
masterPage.ListView.ItemSelected += OnItemSelected;
Detail = new NavigationPage(new Views.HomePage())
{
BarBackgroundColor = Color.Black,
BarTextColor = Color.White,
};
}
public MainPage(string bottomMenu)
{
Master = new MasterPage();
InitializeComponent();
masterPage.ListView.ItemSelected += OnItemSelected;
if ("News" == bottomMenu)
{
Detail = new NavigationPage(new Views.HomePage())
{
BarBackgroundColor = Color.Black,
BarTextColor = Color.White,
};
}
else if ("Profile" == bottomMenu)
{
Detail = new NavigationPage(new Views.Profile())
{
BarBackgroundColor = Color.Black,
BarTextColor = Color.White,
};
}
}
async void OnItemSelected(object sender, SelectedItemChangedEventArgs e)
{
try
{
var item = e.SelectedItem as MasterPageItem;
if (item != null)
{
if (item.Title == "News")
{
Detail = new NavigationPage(new Views.NewsPage())
{
BarBackgroundColor = Color.Black,
BarTextColor = Color.White,
};
}
if (item.Title == "Home")
{
Detail = new NavigationPage(new Views.HomePage())
{
BarBackgroundColor = Color.Black,
BarTextColor = Color.White,
};
}
if (item.Title == "Profile")
{
Detail = new NavigationPage(new Views.Profile())
{
BarBackgroundColor = Color.Black,
BarTextColor = Color.White,
};
}
masterPage.ListView.SelectedItem = null;
IsPresented = false;
}
}
catch (Exception ex)
{
}
}
}}
MasterPage.xaml
<?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="Test.Views.MasterPage"> <ContentPage.Content>
<StackLayout VerticalOptions="FillAndExpand" BackgroundColor="#10000c" Padding = "0,50,0,0" >
<StackLayout x:Name="slUserProfile" Orientation="Vertical" Spacing = "0"
VerticalOptions="FillAndExpand">
<Image Source="{Binding member_image}" x:Name="imgSideImage"
HorizontalOptions="CenterAndExpand" Aspect="AspectFill" HeightRequest="100"
WidthRequest="100" />
<Label Text="{Binding name}" TextColor="#efa747"
FontSize ="17"
HorizontalOptions="CenterAndExpand"/>
</StackLayout >
<ListView x:Name="lvSideMenu" VerticalOptions="FillAndExpand" SeparatorVisibility="None"
BackgroundColor="Black">
<ListView.ItemTemplate>
<DataTemplate>
<ViewCell>
<StackLayout Padding="15,5,0,0" Orientation="Horizontal">
<Image Source="{Binding IconSource}"/>
<StackLayout Padding = "10,0,0,0">
<local:CustomLabel Text="{Binding Title}" VerticalOptions="CenterAndExpand"
TextColor="#dac6ac" FontSize ="14"/>
</StackLayout>
</StackLayout>
</ViewCell>
</DataTemplate>
</ListView.ItemTemplate>
</ListView>
</StackLayout></ContentPage.Content></ContentPage>
MasterPage.xaml.cs
using Xamarin.Forms;namespace Test.Views{
public partial class MasterPage : ContentPage
{
public ListView ListView { get { return lvSideMenu; } }
public Page Detail { get; set; }
public MasterPage()
{
InitializeComponent();
var masterPageItems = new List<MasterPageItem>();
//Fills side menu items.
masterPageItems.Add(new MasterPageItem
{
Title = "Profile",
IconSource = "profile_sidemenu.png"
});
masterPageItems.Add(new MasterPageItem
{
Title = "Home",
IconSource = "home_smenu.png"
});
masterPageItems.Add(new MasterPageItem
{
Title = "News",
IconSource = "news_smenu.png"
});
lvSideMenu.ItemsSource = masterPageItems;
Icon = "menu.png";
Title = "Menu";
}
}
public class MenuItems
{
public string MenuTitle { get; set; }
}
public class MasterPageItem
{
public string Title { get; set; }
public string IconSource { get; set; }
}}
HomePage.xaml
<?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="Test.Views.HomePage" Title="Home"><ContentPage.Content><StackLayout> <Label Text="This is Home page"/></StackLayout></ContentPage.Content></ContentPage>
Profile.xaml
<?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="Test.Views.Profile" Title="Profile"><ContentPage.Content> <StackLayout>
<StackLayout>
<Label Text="This is Profile page" />
</StackLayout>
<StackLayout HeightRequest="80">
<Grid RowSpacing="0" ColumnSpacing="0" VerticalOptions="FillAndExpand" HorizontalOptions="FillAndExpand">
<Grid.ColumnDefinitions>
<ColumnDefinition Width="*"/>
<ColumnDefinition Width="*"/>
</Grid.ColumnDefinitions>
<StackLayout x:Name="tProfile" BackgroundColor="Red" Grid.Column="0" Spacing="0" Padding="0,10,0,10">
<Image Source="bprofileSel.png" HorizontalOptions="Center" VerticalOptions="End"/>
<Label Text="Profile" FontSize="10" TextColor="White" HorizontalOptions="CenterAndExpand" VerticalTextAlignment="Center"/>
</StackLayout>
<StackLayout x:Name="tNews" BackgroundColor="Black" Grid.Column="1" Spacing="0" Padding="0,10,0,10">
<Image Source="bNewsUnsel.png" HorizontalOptions="Center" VerticalOptions="End"/>
<local:CustomLabel Text="News" FontSize="10" TextColor="White" HorizontalOptions="CenterAndExpand" VerticalTextAlignment="Center"/>
</StackLayout>
</Grid>
</StackLayout>
</StackLayout></ContentPage.Content></ContentPage>
Profile.xaml.cs
Using System;using System.Collections.Generic;using System.Linq;using System.Text;using System.Threading.Tasks;using Xamarin.Forms;namespace Test.Views{
public partial class Profile : ContentPage
{
public Profile()
{
InitializeComponent();
try
{
tProfile.GestureRecognizers.Add(new TapGestureRecognizer
{
Command = new Command(() => ProfileClicked()),
});
tNews.GestureRecognizers.Add(new TapGestureRecognizer
{
Command = new Command(() => NewsClicked()),
});
}
catch (Exception ex)
{
}
}
private void ProfileClicked()
{
App.Current.MainPage = new MainPage("Profile");
}
private void NewsClicked()
{
App.Current.MainPage = new MainPage("News");
}
}}
The news page can be set similarly to the profile page. In app.cs, calling MainPage = new MainPage ()
Here, when the app is launched, it will display the HomePage with a side menu. Now when I click on the menu (say profile from the side menu) it takes me to the profile page and as per the design the bottom submenus can be seen. Clicking on it will throw a null exception in your iOS code. This works great in Android. My guess is the main reason because of the re-initialization of the MasterPage for the Master. But I need this requirement to be met that way. Please help me.
This is a bug in iOS Main.cs
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