System.InvalidCastException: 'Specified cast is not valid. Xamarin.Forms

NeidennX 1

Hi Everyone ! i have this project in which i need to Retrieve a list of data, when i click the Retrieve Button, the app enters in break mode and shows me an error saying

System.InvalidCastException: 'Specified cast is not valid.'

Accroding to what i've found the issue is with the ListView block, but im not quite sure, please find it here attached

            <ListView x:Name="ListEstudiantes">  
                <ListView.ItemTemplate>  
                    <DataTemplate>  
                        <TextCell Text="{Binding Name}">                                
                        </TextCell>  
                    </DataTemplate>  
                </ListView.ItemTemplate>  
            </ListView>

If you need a Demo please let me know!

51341-2020-12-25-19-03-32-appmatriculav5-debugging-micro.png

Alessandro Caliaro 4,186 Reputation points

2020-12-26T09:01:50.777+00:00

Where do you set set the ItemSource?
NeidennX 1 Reputation point

2020-12-26T17:33:50.48+00:00

Hi @Alessandro Caliaro im using ItemTemplate only, it is really necessary to use ItemSource ? ive read the documentation about ListViews Here still doesnt says that we gotta use the ItemSource as a mandatory thing, also im following this tutorial over Here in order to create this app, since im really new at this.

Hope you can help me.

Regards

2 answers

Alessandro Caliaro 4,186 Reputation points

2020-12-26T18:40:13.077+00:00

You must have an ObservableCollection and set ItemSource property to the collection, otherwise your listview does not know data to visualize
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1 person found this answer helpful.
NeidennX 1 Reputation point

2020-12-27T02:14:35.15+00:00

Hi @Alessandro Caliaro What do you mean with Observable collection? can you explain i little more on this ? as i said, im super new on this and so far i've been following the Microsoft Documentation and that tutorial i just provided, and i didn't saw anything like that on those links :/ can you provide some steps or maybe if i provide you this [demo][1] you can maybe explain it with a practical example or something ?

Regards

Alessandro Caliaro 4,186 Reputation points

2020-12-27T09:30:08.677+00:00

TestBindingWithListView
you can find the ObserveblaCollection inside the MyPageViewModel.cs

public ObservableCollection<Model> List { get; set; } = new ObservableCollection<Model>();

and the method private void addRows() fills the List

I use csharp to create the page, not xaml, but it's the same...

I set the ItemSource with

lv.SetBinding(ListView.ItemsSourceProperty, "List");

NeidennX 1 Reputation point

2020-12-27T17:39:13.9+00:00

Hi @Alessandro Caliaro I see what you mean, i updated the program and the List View is now working properly according to the specified function, the things is that i need to Search an Student by an specific condition and display the information in the Text Fields, but when i do it the exception pops up, but the List View is working now properly, so im not quite sure how to fix it can you take a look at the Demo please ?

Regards

Alessandro Caliaro 4,186 Reputation points

2020-12-27T18:27:46.173+00:00

I suggest to close this thread , upvote my answer and open a new answer with the new problem

Alessandro Caliaro 4,186 Reputation points

2021-04-29T05:09:13.297+00:00

It's simple.
ListView need an ItemSource. I don't see that you set an ItemSource in your xaml.
Set it!
For example, here the ItemSource is set in the codebehind: Custom

but you can also use it as a normal xml binding.
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Leon Lu (Shanghai Wicresoft Co,.Ltd.) 76,386 Reputation points Microsoft Vendor

2020-12-28T05:44:51.657+00:00

Hello,

Welcome to our Microsoft Q&A platform!

the things is that i need to Search an Student by an specific condition and display the information in the Text Fields, but when i do it the exception pops up, but the List >View is working now properly

Do you meen when you click the btnRetrive, when you will get the Specified cast is not valid. Xamarin.Forms?

If so, you should change txtCedula to txtCedula.Text like following code. Because txtCedula is entry, if you want to get the text from the entry, you could add Text property.

var Estudiante = await FireBaseHelper.GetEstudiante(Convert.ToInt32(txtCedula.Text)).ConfigureAwait(true);

Note: If you solved this issue, please delete the demo link in the comment, it contains your privacy information, If you have any other issues about firebase, you do not share the baseUrl. Just emty it, then share test record's data-structor in firebase DB.

Best Regards,

Leon Lu

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System.InvalidCastException: 'Specified cast is not valid. Xamarin.Forms

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