BindingContext with Parameters from constructor in XAML

Question

I have tryied to find a solution in order to pass a parameter from constructor to ViewModel via XAML only. (If it is possible)

public MainPageViewModel(Model MyModel)
{

}

And then pass in xaml:

<ContentPage.BindingContext>
    <local:MainPageViewModel>
        <x:Arguments>
            <local:Model/>
        </x:Arguments>
    </local:MainPageViewModel>
</ContentPage.BindingContext>

I have tryied this BUT it is creating a new instance of Model instead of passing instance of MyModel... It is possible to achieve this via XAML only ?

Answer 1

Hello,

Welcome to our Microsoft Q&A platform!

From this doc, we can see passing constructor arguments only support basic types, so you couldn't pass Model MyModel by this way. And x:Object couldn't be converted. If you still want to pass value by XAML, you could try to pass basic types or add a property to the ViewModel, refer to the following code:

Basic Types

<ContentPage.BindingContext>  
        <VM:MainPageVM >  
            <x:Arguments>  
                <x:String>4567</x:String>  
                <x:String>123</x:String>  
            </x:Arguments>  
        </VM:MainPageVM>  
    </ContentPage.BindingContext>  

<StackLayout>  
    <!--test the value-->  
        <Button Text="{Binding MyModel.Name}" HorizontalOptions="Center" VerticalOptions="Center" Clicked="Button_Clicked"></Button>  
    <Label Text="{Binding MyModel.ID}"></Label>  
</StackLayout>  

VM

 public class MainPageVM  
    {  
        public MainPageVM()  
        {  
  
        }  
        public MyModel MyModel { get; set; }  
        public MainPageVM(String titleName,String TitleId)  
        {  
            MyModel = new MyModel();  
            MyModel.Name = titleName;  
            MyModel.ID = TitleId;  
        }  
}  

Add a property to the ViewModel

VM

 public class MainPageVM  
    {  
        MyModel _myModel;  
        public event PropertyChangedEventHandler PropertyChanged;  
        public MainPageVM()  
        {  
  
        }  
        public MyModel MyModel  
        {  
            set  
            {  
                if (_myModel != value)  
                {  
                    _myModel = value;  
                    OnPropertyChanged("MyModel");  
                }  
            }  
            get  
            {  
                return _myModel;  
            }  
        }  
        protected void OnPropertyChanged(string propertyName)  
        {  
            PropertyChanged?.Invoke(this, new PropertyChangedEventArgs(propertyName));  
        }  
    }  

Xaml

  <ContentPage.BindingContext>  
        <VM:MainPageVM MyModel="{x:Static VM:App.ModelNow}">  
             
        </VM:MainPageVM>  
    </ContentPage.BindingContext>  

static model

public static MyModel ModelNow { get; set; } = new MyModel { Name = "1111", ID = "AAAA"};//add a static model in APP to test   

Best Regards,
Wenyan Zhang

---

If the answer is the right solution, please click "Accept Answer" and kindly upvote it. If you have extra questions about this answer, please click "Comment".
Note: Please follow the steps in our documentation to enable e-mail notifications if you want to receive the related email notification for this thread.