maui-data-binding（毛伊岛数据绑定）

.NET MAUI Data Binding

Don't specify redundant binding modes

Set Mode explicitly only when overriding the default. Most properties already have the right default:

<!-- ✅ Defaults — omit Mode -->
<Label Text="{Binding Score}" />           <!-- OneWay is the default -->
<Entry Text="{Binding UserName}" />        <!-- TwoWay is the default -->
<Switch IsToggled="{Binding DarkMode}" />  <!-- TwoWay is the default -->

<!-- ✅ Override when needed -->
<Label Text="{Binding Title, Mode=OneTime}" />
<Entry Text="{Binding SearchQuery, Mode=OneWayToSource}" />

<!-- ❌ Redundant — just noise -->
<Label Text="{Binding Score, Mode=OneWay}" />
<Entry Text="{Binding UserName, Mode=TwoWay}" />

Compiled bindings — x:DataType placement rules

Compiled bindings are 8–20× faster than reflection-based bindings. Enable with x:DataType.

Place x:DataType only where BindingContext is set:

1. Page root — where you assign BindingContext.
2. DataTemplate — which creates a new binding scope.

Do not scatter x:DataType on child elements. Adding x:DataType="x:Object" on children to "escape" compiled bindings is an anti-pattern — it disables compile-time checking and reintroduces reflection. To opt out for a single binding, use x:DataType="{x:Null}" on that element (see also: maui-xaml-authoring skill).

<!-- ✅ Correct: x:DataType only where BindingContext is set -->
<ContentPage x:DataType="vm:MainViewModel">
    <VerticalStackLayout>
        <Label Text="{Binding Title}" />
        <Slider Value="{Binding Progress}" />
    </VerticalStackLayout>
</ContentPage>

<!-- ❌ Wrong: x:DataType scattered on children -->
<ContentPage x:DataType="vm:MainViewModel">
    <VerticalStackLayout>
        <Label Text="{Binding Title}" />
        <Slider x:DataType="x:Object" Value="{Binding Progress}" />
    </VerticalStackLayout>
</ContentPage>

DataTemplate always needs its own x:DataType:

<CollectionView ItemsSource="{Binding People}">
    <CollectionView.ItemTemplate>
        <DataTemplate x:DataType="model:Person">
            <Label Text="{Binding FullName}" />
        </DataTemplate>
    </CollectionView.ItemTemplate>
</CollectionView>

Treat compiler warnings as errors in CI

<WarningsAsErrors>XC0022;XC0025</WarningsAsErrors>

.NET 9+ compiled code bindings

Fully AOT-safe, no reflection:

label.SetBinding(Label.TextProperty,
    static (PersonViewModel vm) => vm.FullName);

entry.SetBinding(Entry.TextProperty,
    static (PersonViewModel vm) => vm.Age,
    mode: BindingMode.TwoWay,
    converter: new IntToStringConverter());

Threading caveat

MAUI automatically marshals PropertyChanged to the UI thread — you can raise it from any thread. However, direct ObservableCollection mutations (Add/Remove) from background threads may still crash:

// ✅ Safe for PropertyChanged
await Task.Run(() => Items = LoadData());

// ⚠️ ObservableCollection.Add — dispatch to UI thread
MainThread.BeginInvokeOnMainThread(() => Items.Add(newItem));

Performance tips

• Compiled bindings eliminate reflection — always prefer them.
• NativeAOT / trimming: Reflection-based bindings break under trimming. Compiled bindings (XAML x:DataType or code SetBinding with lambdas) are trimmer- and AOT-safe.
• Use OneTime mode for truly static data to skip change-tracking registration.
• Avoid complex converter chains in hot paths — pre-compute values in the ViewModel instead.