Xamarin performance

Question

Hello

I am trying to get the most out of my app, so I decided to use Compile Bindings, but I have a problem.

Compile bindings will prevent your app f running if the property does not exist in your VM

For example:

I manage to achieve this on my login page

 <StackLayout x:DataType="vm:LoginViewModel">
        <StackLayout.BindingContext>
            <vm:LoginViewModel />
        </StackLayout.BindingContext>
        <Path Aspect="Fill" 
  Stroke="#007fff"
  Fill="#007fff"
  Data="m166.17002,57.2175l501.99997,0l0,104.7864c-272.99998,-68 -170.99998,126.92554 -501.99997,17.24058l0,-122.02698z"/>
            <Path Aspect="Uniform"
  Fill="#007fff"
  Stroke="#007fff"
  Data="M55,27.5C55,12.337,42.663,0,27.5,0S0,12.337,0,27.5c0,8.009,3.444,15.228,8.926,20.258l-0.026,0.023l0.892,0.752
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C42.677,47.979,42.567,48.054,42.459,48.132z"/>
            <Entry Placeholder="Email"
   Text="{x:Binding User.Email, Mode=TwoWay}"
   Margin="20,10,20,0"/>
            <Entry Placeholder="Password"
   Text="{x:Binding User.Password, Mode=TwoWay}"
   Margin="20,10,20,0"/>
            <Button Text="Login"
Command="{x:Binding Login}"
IsEnabled="{x:Binding LoginAllowed, Mode=TwoWay}"
Margin="20,30,20,0"/>
            <Label Text="Do not have an account"
   HorizontalTextAlignment="Center"
   FontSize="16"
   TextColor="CornflowerBlue"
   Margin="0,30,0,0">
                <Label.GestureRecognizers>
                    <TapGestureRecognizer Command="{x:Binding OpenPopupCommand}"/>
                </Label.GestureRecognizers>
            </Label>
            <sfPopup:SfPopupLayout Visual="Material" 
   StaysOpen="True"
   ClosePopupOnBackButtonPressed="False"
   x:Name="popUpLayout" IsOpen="{x:Binding DisplayPopUp}">
                <sfPopup:SfPopupLayout.PopupView>
                    <sfPopup:PopupView HeaderHeight="60"
   AutoSizeMode="Height"
   HeaderTitle="Sign In"
   ShowFooter="False"
   AnimationMode="SlideOnBottom">
                        <sfPopup:PopupView.PopupStyle>
                            <sfPopup:PopupStyle HeaderFontAttribute="Bold"
HeaderBackgroundColor="#0D0D41"
HeaderFontSize="20"
HeaderTextAlignment="Center"
HeaderTextColor="White"/>
                        </sfPopup:PopupView.PopupStyle>
                        <sfPopup:PopupView.ContentTemplate>
                            <DataTemplate>
                                <StackLayout Spacing="20"
 Padding="10">
                                    <Entry Placeholder="Email"
   Text="{x:Binding User.Email, Mode=TwoWay}"/>
                                    <Entry Placeholder="Password"
   Text="{x:Binding User.Password, Mode=TwoWay}"/>
                                    <Entry Placeholder="Confirm Password"
   Text="{x:Binding User.ConfirmPassword, Mode=TwoWay}"/>
                                    <Button Text="Sign in"
Command="{x:Binding Register}"
IsEnabled="{x:Binding RegisterAllowed, Mode=TwoWay}"/>
                                </StackLayout>
                            </DataTemplate>
                        </sfPopup:PopupView.ContentTemplate>
                    </sfPopup:PopupView>
                </sfPopup:SfPopupLayout.PopupView>
                <sfPopup:SfPopupLayout.Content>
                    <StackLayout x:Name="mainLayout">
                        <Button x:Name="clickToShowPopup"
                                Text="ClickToShowPopup"
                                VerticalOptions="Start"
                                HorizontalOptions="FillAndExpand" />
                    </StackLayout>
                </sfPopup:SfPopupLayout.Content>
            </sfPopup:SfPopupLayout>
        </StackLayout>
</ContentPage>

Now if a put a wrong binding, the app will throw an error and not compile.

I want to do the same here, but since I have a listview I don't know-how

     <ContentPage.BindingContext>
        <vm:NotebooksVM/>
    </ContentPage.BindingContext>

    <ContentPage.Content>
        <StackLayout x:DataType="vm:NotebooksVM">
            <syncfusion:SfListView x:Name="NoteBookLV" 
                                      AutoFitMode="Height" 
                                      ItemsSource="{x:Binding NotebooksCollection}"
                                      SelectionChangedCommand="{x:Binding SelectedNoteBookCommand}"
                                      SelectedItem="{x:Binding SelectedNotebook}">
                <syncfusion:SfListView.ItemTemplate>
                    <DataTemplate x:DataType="vm:NotebooksVM">
                        <Grid Padding="5" RowDefinitions="20,50">
                            <Label Text="{x:Binding CreatedAt, StringFormat='Created on: {0}'}"
                                   FontAttributes="Bold"
                                   BackgroundColor="Gray"/>
                            <StackLayout Grid.Row="1"
                                         Orientation="Horizontal">
                                <Label Text="{x:Static fi:IconFonts.Notebook}"
                                       FontFamily="material" 
                                       VerticalTextAlignment="Center"
                                       FontSize="40"/>
                                <Label Text="{x:Binding Name,StringFormat='Name: {0}'}"
                                       FontAttributes="Bold"
                                       VerticalTextAlignment="Center"/>
                            </StackLayout>
                        </Grid>
                    </DataTemplate>
                </syncfusion:SfListView.ItemTemplate>
            </syncfusion:SfListView>
            <Button Text="{x:Static fi:IconFonts.Plus}" 
                    FontSize="30"
                    HorizontalOptions="EndAndExpand"
                    WidthRequest="50"
                    HeightRequest="50"
                    BorderWidth="2"
                    BorderColor="Gray"
                    CornerRadius="100"
                    Margin="30"
                    FontFamily="material"
                    Command="{x:Binding CreateNewNotebook}"
                    VerticalOptions="End"/>
        </StackLayout>
    </ContentPage.Content>
</ContentPage>

Update 2

I did this

  <ContentPage.BindingContext>
        <vm:NotebooksVM/>
    </ContentPage.BindingContext>

    <ContentPage.Content>
        <StackLayout x:DataType="vm:NotebooksVM">
            <syncfusion:SfListView x:Name="NoteBookLV" 
                                      AutoFitMode="Height" 
                                      ItemsSource="{x:Binding NotebooksCollection}"
                                      SelectionChangedCommand="{x:Binding SelectedNoteBookCommand}"
                                      SelectedItem="{x:Binding SelectedNotebook}">
                <syncfusion:SfListView.ItemTemplate>
                    <DataTemplate x:DataType="vm:NotebooksVM">
                        <Grid Padding="5" RowDefinitions="20,50">
                            <Label Text="{x:Binding CreatedAt, StringFormat='Created on: {0}'}"
                                   FontAttributes="Bold"
                                   BackgroundColor="Gray"/>
                            <StackLayout Grid.Row="1"
                                         Orientation="Horizontal">
                                <Label Text="{x:Static fi:IconFonts.Notebook}"
                                       FontFamily="material" 
                                       VerticalTextAlignment="Center"
                                       FontSize="40"/>
                                <Label Text="{x:Binding Name,StringFormat='Name: {0}'}"
                                       FontAttributes="Bold"
                                       VerticalTextAlignment="Center"/>
                            </StackLayout>
                        </Grid>
                    </DataTemplate>
                </syncfusion:SfListView.ItemTemplate>
            </syncfusion:SfListView>
            <Button Text="{x:Static fi:IconFonts.Plus}" 
                    FontSize="30"
                    HorizontalOptions="EndAndExpand"
                    WidthRequest="50"
                    HeightRequest="50"
                    BorderWidth="2"
                    BorderColor="Gray"
                    CornerRadius="100"
                    Margin="30"
                    FontFamily="material"
                    Command="{x:Binding CreateNewNotebook}"
                    VerticalOptions="End"/>
        </StackLayout>
    </ContentPage.Content>
</ContentPage>

and is telling me that "Name does not exist"

Answer 1

Hi EduardoGomez-1870,

Welcome to our Microsoft Q&A platform!

The role of x:DataType is to specify the type of data bound later, but it will not bind any data source. After setting x:DataType, the compiler will automatically determine whether the attribute exists and provide IntelliSense. For example, if you set the x:DataType for "DataTemplate", the IntelliSense will provide tip "Name" when you type 'N' .

<DataTemplate x:DataType="model:NoteBook">  
        <StackLayout>  
            <Label Text="{Binding Name}"/>  
            <Label Text="{Binding Num}"/>  
        </StackLayout>  
</DataTemplate>  

To achieve data binding, you must set the BindingContext for each Page. So that the corresponding data can be displayed on the page.
You can set the BindingContext in XAML, like you tried before.

<ContentPage.BindingContext>  
    <vm:NotesVM/>  
</ContentPage.BindingContext>  

Or bind it programmatically in Page.xaml.cs.

public MainPage()  
{  
    InitializeComponent();  
    this.BindingContext = new NotesVM();  
}  

More info about Data Binding, refer to Data Binding.

Regards,
Kyle

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