Xamarin Forms crossPlatform: force to repaint - xamarin.forms

Question

I know i know: probably it is one of the most asked questions. Before you send me some LMGTFY links, let me tell that I've been some hours with this question, and I've made some tries with Invalidate, PostInvalidate, RunOnUIThread, etc; with no success. I do not discard that the solution can be one of the previously mentioned, and I have not been using it properly. I am actually learning Xamarin, doing my first crossplatform app, so my knowledge of the framework is very poor.
So now let's go to my concrete problem, and let's see if someone can help me. I want a intro page for my app, with a progress bar and a text below saying what is doing the app (when starting the app, it calls a WS to download changes, and has to load info from text files and put it into some static data structures to use for all pages). What i want to do in the loading page is the following sequence:
1. Change text to tell what is the app doing.
2. Call WS or load a file.
3. Update progress bar.
4. Go to next update or to the welcome page if all is loaded.
What i get for my actual code is that the page is load when all the stuff is done, so I see the progress bar completed and the last text change. But is a static page, i don't see the progress bar growing neither the text changing.
This is my code:
public partial class LoadingPage : ContentPage
{
InitializeComponent();
this.lpb.Text = "Connecting to web server to check updates";
App.localInfo.updateInfo(); //Connect web server to check updates
this.pb.Progress = 0.2;
this.lpb.Text = "Loading info from local files";
App.localInfo.cargarInfo(); //Load local files to memory for quick access
this.pb.Progress = 0.7;
this.lpb.Text = "Doing other stuff"; //This is only for proves
Task.Run(async () =>
{
await Task.Delay(2000);
});
this.pb.Progress = 1;
this.lpb.Text = "Load completed. The app will start now";
}
And this is my ContentPage:
<?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="Prueba1.Views.LoadingPage">
<ContentPage.Content>
<StackLayout>
<ProgressBar x:Name="pb" Progress="0.0" ProgressColor="Red"/>
<Label x:Name="lpb" Text="Welcome to Xamarin.Forms!"/>
</StackLayout>
</ContentPage.Content>
</ContentPage>
This is only the alpha version. I would like to concrete a little more, because I have to load around 10 different text files, and I would like to update progress bar and label inside the App.localInfo methods. But first I have to learn how to do this simple stuff, and then trying something more complicated.
Thanks in advance!

Answer 1

Instead of setting the progress property like you are, try using the progress bar's ProgressTo method inside an async method. Something like:
public MainPage()
{
InitializeComponent();
FireProgressBar();
}
async void FireProgressBar()
{
lpb.Text = "Connecting to web server to check updates";
// Task.Delay to simulate network call.
await Task.Delay(2000);
await pb.ProgressTo(.2, 250, Easing.Linear);
lpb.Text = "Loading info from local files";
// Task.Delay to simulate network call.
await Task.Delay(2000);
await pb.ProgressTo(.7, 250, Easing.Linear);
lpb.Text = "Doing other stuff";
// Task.Delay to simulate network call.
await Task.Delay(2000);
await pb.ProgressTo(1.0, 250, Easing.Linear);
lpb.Text = "Load completed. The app will start now";
}
This has the added benefit of actually seeing the progress bar moving, not just jerking from one value to the next.