Xamarin.ios：在.Split（“，”）之后列出要跳过的代码的字符串

Question

I'm building an iOS app with Xamarin.ios MvvmCross. And I Accomplished to convert the string into a list with .Split(',') . Now when I run my code and I want to see the list in my app. The first time I click on an item the viewcell will skip the code after running line string[] namesArray = FavoriteContent.ingredients.Split(','); . When I go back to the table view and push the viewcell again. It will run the code and display the list.

The code I display below is in my viewmodel in the .Core project. And I call it in de .IOS project in de views.

Code to make from a string a list and return it:

private string _ingredients;

    public string Ingredients
    {
        get
        {
            string[] namesArray = FavoriteContent.ingredients.Split(',');
            List<string> namesList = new List<string>(namesArray.Length);
            namesList.AddRange(namesArray);
            namesList.Reverse();
            _ingredients = string.Join("\n", namesList);
            return _ingredients;
        }
    }

This is where I call the list from my views in the .ios project to the .Core project in the viewmodels

ViewController (5th line I call the list):

MvxFluentBindingDescriptionSet<DetailFavoriteView, DetailFavoriteViewModel> set = new MvxFluentBindingDescriptionSet<DetailFavoriteView, DetailFavoriteViewModel>(this);
        set.Bind(NameRecipe).To(res => res.FavoriteContent.name);
        set.Bind(DetailImage).For(img => img.Image).To(res => res.FavoriteContent.thumbnail).WithConversion<StringToImageConverter>();
        set.Bind(DescriptionText).To(res => res.FavoriteContent.description);
        set.Bind(IngredientsList).To(res => res.Ingredients);
        set.Bind(ConditionText).To(res => res.Conditions);
        set.Bind(ButtonShopList).To(res => res.PostShopListCommand);
        set.Apply();

Answer 1

Because FavoriteContent.ingredients is null you'll get an exception in this line FavoriteContent.ingredients.Split(','); that will be catched in the binding and therefore your viewcell won't display that content. At the second time your FavoriteContent.ingredients is surely not null so it can update the viewcell.

So I think you should just add a null check before doing your logic with FavoriteContent.ingredients to avoid the exception:

private string _ingredients;

public string Ingredients
{
    get
    {
        if (FavoriteContent?.ingredients == null) // IDK if FavoriteContent is a property or a class, I assumed is a property
            return null; // or return string.empty;

        string[] namesArray = FavoriteContent.ingredients.Split(',');
        List<string> namesList = new List<string>(namesArray.Length);
        namesList.AddRange(namesArray);
        namesList.Reverse();
        _ingredients = string.Join("\n", namesList);
        return _ingredients;
    }
}

And then when you load FavoriteContent.ingredients you just tell the view to refresh that binding using RaisePropertyChanged :

// this is the part where you update FavoriteContent.ingredients in your ViewModel so that it is not null
FavoriteContent.ingredients = "my string, my other string, 2, 3";
RaisePropertyChanged(() => Ingredients); // you tell the view Ingredients has changed (make sure you are invoking this in your main thread if not use InvokeOnMainThread(() => RaisePropertyChanged(() => Ingredients));)

HIH