Xamarin Forms -> Activity Indicator not working if Commands of statements to be executed - xamarin.forms

Question

Using Visual Studio 2017 Community 15.8.1
This is after going through all options of stackoverflow regarding ActivityIndicator. So though it may be a duplication but nothing is helping me out.
So finally decided to post my workouts and get best help from here.
What I have tried till now:-
1. {Binding IsLoading} + INotifyPropertyChanged + public void RaisePropertyChanged(string propName) + IsLoading = true; concept.
2. ActivityIndicator_Busy.IsVisible = false; (Direct control accessed)
These two approaches were mostly recommended and I went into depth of each since lot of hours in last few weeks. But nothing got crack.
What I achieved?:-
ActivityIndicator_Busy.IsVisible = false; concept is working smooth only when I put return before executing the statements (for testing purpose); statement on Button Clicked event. (Attached Image)
But as soon as I remove the return; On Pressing Button, directly after some pause, the HomePage Opens.
MY Questions:-
1. This is particular with the current scenario how to get the ActivityIndicator run Immediately when user clicks the Welcome Button.
2. Pertaining to same, When app starts there is also a blank white screen coming for few seconds almost 30 seconds which I also I want to show ActivityIndicator. But dont know how to impose that logic at which instance.
My Inputs
My MainPage.xaml File:-
(Edited 06-Sept-2018 09.11 pm)
<?xml version="1.0" encoding="utf-8" ?>
<ContentPage x:Name="page_main_page"
NavigationPage.HasBackButton="False"
NavigationPage.HasNavigationBar="False"
xmlns="http://xamarin.com/schemas/2014/forms"
xmlns:x="http://schemas.microsoft.com/winfx/2009/xaml"
xmlns:local="clr-namespace:appNutri"
BindingContext="{x:Reference page_main_page}"
x:Class="appNutri.MainPage">
<ContentPage.Content>
<StackLayout BackgroundColor="White"
HorizontalOptions="FillAndExpand"
VerticalOptions="FillAndExpand">
<StackLayout>
<Image x:Name="Image_Welcome"
Source="welcome.png"
HorizontalOptions="CenterAndExpand"
VerticalOptions="CenterAndExpand"
WidthRequest="300"
HeightRequest="300" />
<Button x:Name="Button_Welcome"
Clicked="Button_Welcome_Clicked"
Text="Welcome!"
BackgroundColor="DeepSkyBlue"
HorizontalOptions="CenterAndExpand"
VerticalOptions="CenterAndExpand"
TextColor="White"
HeightRequest="60" />
</StackLayout>
<StackLayout BackgroundColor="White"
HorizontalOptions="FillAndExpand"
VerticalOptions="FillAndExpand">
<ActivityIndicator
x:Name="ActivityIndicator_Busy"
Color="Black"
IsEnabled="True"
HorizontalOptions="Center"
VerticalOptions="Center"
IsRunning="{Binding Source={x:Reference page_main_page}, Path=IsLoading}"
IsVisible="{Binding Source={x:Reference page_main_page}, Path=IsLoading}" />
</StackLayout>
</StackLayout>
</ContentPage.Content>
</ContentPage>
My MainPage.cs Code:-
(Edited on 06-Sept-2018 09.13 pm)
using appNutri.Model;
using SQLite;
using System;
using System.Collections.Generic;
using System.ComponentModel;
using System.Data;
using System.Data.SqlClient;
using System.IO;
using System.Linq;
using System.Text;
using System.Threading.Tasks;
using Xamarin.Forms;
namespace appNutri
{
public partial class MainPage : Xamarin.Forms.ContentPage, INotifyPropertyChanged
{
private bool isLoading;
public bool IsLoading
{
get
{
return isLoading;
}
set
{
isLoading = value;
RaisePropertyChanged("IsLoading");
}
}
public event PropertyChangedEventHandler PropertyChanged;
public void RaisePropertyChanged(string propName)
{
if (PropertyChanged != null)
{
PropertyChanged(this, new PropertyChangedEventArgs(propName));
}
}
public MainPage()
{
InitializeComponent();
BindingContext = this;
}
protected override void OnAppearing()
{
base.OnAppearing();
BindingContext = this;
}
protected async void Button_Welcome_Clicked(object sender, EventArgs e)
{
IsLoading = true;
await Select_Local_User_Information();
IsLoading = false;
}
private async Task Select_Local_User_Information()
{
IsLoading = true;
string where_clause = "";
try
{
Sql_Common.Database_Folder_Path = System.Environment.GetFolderPath(System.Environment.SpecialFolder.Personal);
string Database_Full_Path = Path.Combine(Sql_Common.Database_Folder_Path, Sql_Common.Database_Name);
SQLiteConnection connection = new SQLiteConnection(Database_Full_Path);
//connection.DropTable<User_Master>();
//connection.Delete(connection.Table<User_Master>());
//connection.CreateTable<User_Master>(CreateFlags.ImplicitPK | CreateFlags.AutoIncPK);
connection.CreateTable<User_Master>();
int count = connection.ExecuteScalar<int>("Select count(*) from User_Master");
if (count == 0)
{
connection.DropTable<User_Master>();
connection.CreateTable<User_Master>();
//IsLoading = false;
//IsBusy = false;
await Navigation.PushAsync(new User_Register_Page());
}
else
{
Sql_Common.User_Logged = true;
var Local_User_Data = connection.Table<User_Master>().ToList();
User_Master.Logged_User_Details_Container.First_Name = Local_User_Data[0].First_Name;
User_Master.Logged_User_Details_Container.Cell1 = Local_User_Data[0].Cell1;
where_clause = " Upper ( First_Name ) = " + "'" + User_Master.Logged_User_Details_Container.First_Name.ToUpper().Trim() + "'" + " and " +
" Cell1 = " + "'" + User_Master.Logged_User_Details_Container.Cell1.Trim() + "'";
int records = Sql_Common.Get_Number_Of_Rows_Count("User_Master", where_clause);
if (records == 0)
{
connection.DropTable<User_Master>();
connection.CreateTable<User_Master>();
IsLoading = false;
await Navigation.PushAsync(new User_Register_Page());
}
else
{
User_Master.User_Master_Table(where_clause, User_Master.Logged_User_Details_Container);
IsLoading = false;
await Navigation.PushAsync(new User_Home_Page());
}
}
connection.Close();
}
catch (SQLiteException ex)
{
string ex_msg = ex.Message;
}
IsLoading = false;
}
}
}
04-Oct-2018
Finally resolved with This Answer

Answer 1

Update 2018-09-10
You think that you have implemented INotifyPropertyChanged by adding INotifyPropertyChanged to your class definition and adding the event
public event PropertyChangedEventHandler PropertyChanged;
along with its event invocator
public void RaisePropertyChanged(string propName)
{
if (PropertyChanged != null)
{
PropertyChanged(this, new PropertyChangedEventArgs(propName));
}
}
Anyway, since ContentPage already implements INotifyPropertyChanged, adding those did not implement INotifyPropertyChanged. ContentPage already defines the event (or rather BindableObjectfrom which ContentPage indirectly inherits). Any object that relies on being informed about property changes in your page will subscribe to the PropertyChanged event of the ancestor and not the PropertyChanged event you defined, hence the ActivityIndicator will not update.
Just remove the event you defined and call OnPropertyChanged instead of RaisePropertyChanged() and you should be fine.
private bool isLoading;
public bool IsLoading
{
get
{
return isLoading;
}
set
{
isLoading = value;
OnPropertyChanged();
}
}
Since OnPropertyChanged is declared as
protected void OnPropertyChanged([CallerMemberName] string propertyName = null)
you don't have to pass the property name by hand. The compiler will do that for you beacsue of the CallerMemberNameAttribute.
End Update
The XAML extension {Binding IsLoading} binds the ActivityIndicator to the BindingContext of your page. By default the BindingContext is null, hence there is nothing to bind to and all your efforts are to no avail.
With a viewmodel
The preferred solution would be to use a viewmodel and assign it to MainPage.BindingContext, e.g.
var page = new MainPage()
{
BindingContext = new MainPageViewModel()
}
but if you take that road, you should move all of your UI logic to that viewmodel and encapsulate your SQL access and business logic in other classes, to keep the viewmodel clean from resource accesses and business logic. Having the resource accesses and logic in code behind may work for that small example, but is likely to become an unmaintainable mess.
Without a viewmodel
Anyway, you don't have to use a viewmodel to use bindings. You can set the BindingContext for the page (or some children) or use the Source of the BindingExtension
Setting the BindingContext
The BindingContext is passed from any page or view to it's children. You first have to give your page a name with x:Name="Page" (don't have to use Page, anyway, you can't use the class name of your page) and set the BindingContext to that page
<ContentPage ...
x:Name="Page"
BindingContext="{x:Reference Page}"
...>
now binding to IsLoading should work.
Using Source in the Binding
If you want to reference something else than the BindingContext of a view, BindingExtension has a property Source. You have to give a name to your page, too (see above)
<ContentPage ...
x:Name="Page"
...>
and now you can reference this in your binding
<ActivityIndicator
...
IsRunning="{Binding Path=IsLoading, Source={x:Reference Page}}"
IsVisible="{Binding Path=IsLoading, Source={x:Reference Page}}"/>