CODEWITHSUNDEEP
c#xamarinxamarin.forms
KalleP
KalleP

Reputation: 329

Run code once upon entering page

I'm running this code when entering a page:

protected override async void OnAppearing()
     {
         base.OnAppearing();

         Title = wasteObject.WasteType;

         foreach (var i in wasteDescription)
         {
             if (i.description_Id == wasteObject.Waste_Id)
             {
                 await viewModel.getDescription(i.wasteImage, i.sortName, i.wasteDescription, myWebView, (error) => 
                 {
                     if(error != null)
                     {
                         DisplayAlert("Problem", "Not possible", "Ok");
                     }
                 });
             }
         }

     }

The issue I'm having is that when I leave that page and get back to it. It has created 2 blocks with text (same text in both blocks). So what I wanna do is to run the code once to prevent more than one block of text to show.

Appreciate all the help, thanks.

Upvotes: 1

Views: 63

Answers (2)

Mukesh Modhvadiya
Mukesh Modhvadiya

Reputation: 2178

As @mjwills said in comment, use boolean field to indicate if the code is already executed. Declare field outside the method OnAppearing

private bool isTextBlockCreated = false;

Then put the code that needs to be run only once in condition check with isTextBlockCreated

if(!isTextBlockCreated)
{
    foreach (var i in wasteDescription)
         {
             if (i.description_Id == wasteObject.Waste_Id)
             {
                 await viewModel.getDescription(i.wasteImage, i.sortName, i.wasteDescription, myWebView, (error) => 
                 {
                     if(error != null)
                     {
                         DisplayAlert("Problem", "Not possible", "Ok");
                     }
                 });
             }
         }

    isTextBlockCreated = true;
}

That should stop running it multiple times.

Upvotes: 3

Ahmad ElMadi
Ahmad ElMadi

Reputation: 2617

As @LeRoy said you can run it in the constructor that runs Init which calls viewModel.getDescription() . 

protected override async void OnBindingContextChanged()
        {
            base.OnBindingContextChanged();
            if (BindingContext is MyPageViewModel viewModel)
            {
                        foreach (var i in wasteDescription)
             {
            if (i.description_Id == wasteObject.Waste_Id)
                 {
                     await viewModel.getDescription(i.wasteImage, i.sortName, i.wasteDescription, myWebView, (error) => 
                     {
                         if(error != null)
                         {
                             DisplayAlert("Problem", "Not possible", "Ok");
                         }
                     });
                 }
            }

The other way to do it , is that since you have OnAppearing there is also OnDisappearing , and then you can remove the blocks which has been added by the Appearing.

Upvotes: 0

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