How to get value on another page from firstpage binding context

Question

Hello how to get value from BmiPage to HomePage here is my code.

BmiViewModel

public class BmiViewModel : INotifyPropertyChanged
{
public double height = 160;
public double weight = 60;

    public event PropertyChangedEventHandler PropertyChanged;
    public void RaisePropertyChanged(string propertyName)
    {
        PropertyChanged?.Invoke(this, new PropertyChangedEventArgs(propertyName));
    }
    public double Height
    {
        get => height;
        set
        {
            height = value;
            RaisePropertyChanged(nameof(Bmi));
            RaisePropertyChanged(nameof(Classification));
        }
    }
    public double Weight
    {
        get => weight;
        set
        {
            weight = value;
            RaisePropertyChanged(nameof(Bmi));
            RaisePropertyChanged(nameof(Classification));
        }
    }


    public double Bmi

    => Math.Round(Weight / Math.Pow(Height /100, 2), 2);

     public string Classification
    {
        get
        {

            if (Bmi < 18.5)
                return "Underweight";
            else if (Bmi < 25)
                return "Normal";
            else if (Bmi < 30)
                return "Overweight";
            else return "Obese";
        }
    }
}

HomePage.xaml
<Label FontSize="22" Text="{Binding Bmi}" TextColor="Black" />

BmiPage.xaml
<StackLayout>
<Grid Margin="20,0,20,0" ColumnSpacing="2">
<Grid.RowDefinitions >
<RowDefinition Height="AUTO"/>
<RowDefinition Height="AUTO"/>
<RowDefinition Height="AUTO"/>
<RowDefinition Height="AUTO"/>
<RowDefinition Height="AUTO"/>
<RowDefinition Height="AUTO"/>
<RowDefinition Height="AUTO"/>
</Grid.RowDefinitions>

                <Grid.ColumnDefinitions>
                    <ColumnDefinition Width="*" />
                    <ColumnDefinition Width="*" />

                </Grid.ColumnDefinitions>


                <Label Text="BMI Calculator" Margin="20" TextColor="Black"  FontSize="30" HorizontalTextAlignment="Center" Grid.Row="0" Grid.ColumnSpan="2" />
                <Label Text="weight" Margin="20" TextColor="Black"  FontSize="30" HorizontalTextAlignment="Center" Grid.Row="1" Grid.ColumnSpan="2" />
                <Entry Placeholder="your weight" Text="{Binding Weight}" x:Name="txtWeigh"  Grid.Row="2" Grid.ColumnSpan="2" />
                <Label Text="hieght" Margin="20" TextColor="Black"  FontSize="30" HorizontalTextAlignment="Center" Grid.Row="3" Grid.ColumnSpan="2" />
                <Entry Placeholder="your height" Text="{Binding Height}" x:Name="txtHeigh" Grid.Row="4" Grid.ColumnSpan="2"/>
                <Label Text="Your bmi" FontSize="22"  TextColor="Black" Grid.Row="5" Grid.Column="0"/>
                <Label  FontSize="22"  Text="{Binding Bmi, Mode=TwoWay}" TextColor="Black" x:Name="txtSum"  Grid.Row="5" Grid.Column="1" />
                <Label  FontSize="22"  Text="Overweight or not" TextColor="Black"   Grid.Row="6" Grid.Column="0" />

                <Label  FontSize="22"  Text="{Binding Classification}" TextColor="Black"  Grid.Row="6" Grid.Column="1" />

            </Grid>
        </StackLayout>

Answer 1

Hello,

Welcome to our Microsoft Q&A platform!

There are several methods to achieve this based on your requirement. I list two ways below:

1.pass data by constructor of the next page. Please refer to the following code:

BmiPage.xaml.cs

public partial class BmiPage : ContentPage  
{  
    BmiViewModel viewModel;  

    public BmiPage()  
    {  
        InitializeComponent();  

        viewModel = new BmiViewModel();  
        BindingContext = viewModel;  
    }  

    private async void Button_Clicked(object sender, EventArgs e)  
    {  
        await Navigation.PushModalAsync(new HomePage(viewModel.Bmi));  
    }  

}  

HomePage.xaml.cs

public partial class HomePage : ContentPage  
{  
    public double Bmi { get; set; }  
    public HomePage(double bmi )  
    {  
        InitializeComponent();  

        Bmi = bmi;  

        BindingContext = this;  
    }  
}  

2.create a new Viewmodel for HomePage and set BindingContext for it.

create Viewmodel HomeViewModel.cs for HomePage:

public class HomeViewModel: INotifyPropertyChanged  
{  
    double bmi;  

    public double Bmi  
    {  
        set { SetProperty(ref bmi, value); }  

        get { return bmi; }  
    }  

    public HomeViewModel(double bmi) {  

        Bmi = bmi;  
    }  

    bool SetProperty<T>(ref T storage, T value, [CallerMemberName] string propertyName = null)  
    {  
        if (Object.Equals(storage, value))  
            return false;  

        storage = value;  
        OnPropertyChanged(propertyName);  
        return true;  
    }  

    protected void OnPropertyChanged([CallerMemberName] string propertyName = null)  
    {  
        PropertyChanged?.Invoke(this, new PropertyChangedEventArgs(propertyName));  
    }  

    public event PropertyChangedEventHandler PropertyChanged;  
}  

BmiPage.xaml.cs

public partial class BmiPage : ContentPage  
{  
    BmiViewModel viewModel;  

    public BmiPage()  
    {  
        InitializeComponent();  

        viewModel = new BmiViewModel();  
        BindingContext = viewModel;  
    }  

    private async void Button_Clicked(object sender, EventArgs e)  
    {  
        //await Navigation.PushModalAsync(new HomePage(viewModel.Bmi));  
        await Navigation.PushModalAsync(new HomePage {  
            BindingContext = new HomeViewModel(viewModel.Bmi)  
        });  
    }  
}  

Best Regards,

Jessie Zhang

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