我应该在WPF中使用自定义控件声明绑定选项

Question

I'm new to make custom control in wpf.
I quite don't understand binding technique with custom control.
Let me show you my exercise.

I declare my custom control in cs file

public class CustomControl1 : Control
{
    static CustomControl1()
    {
        DefaultStyleKeyProperty.OverrideMetadata
            (typeof(CustomControl1), new FrameworkPropertyMetadata(typeof(CustomControl1))
            );
    }

    // Using a DependencyProperty as the backing store for Text.  This enables animation, styling, binding, etc...
    public static readonly DependencyProperty TextaaProperty =
        DependencyProperty.Register(
            "Textaa", 
            typeof(string), typeof(CustomControl1),
            new PropertyMetadata(null));

    public string Textaa
    {
        get { return (string)GetValue(TextaaProperty); }
        set { SetValue(TextaaProperty, value); }
    }
 }

and in Generic.xaml, I declared Template Style for my custom control in Generic.xaml.

<Style TargetType="{x:Type local:CustomControl1}">
    <Setter Property="Background" Value="DimGray"/>
    <Setter Property="Template">
        <Setter.Value>
            <ControlTemplate TargetType="{x:Type local:CustomControl1}">
                <TextBox Background="{TemplateBinding Background}" 
                           Text="{Binding Textaa, 
                                 RelativeSource={RelativeSource TemplatedParent}}">
                </TextBox>
            </ControlTemplate>
        </Setter.Value>
    </Setter>
</Style>

To Text my control, I made My Custom class for Data object that just have name property and just be inherited from INPC

    public MainWindow()
    {
        InitializeComponent();
        DataContext = new DataObject() { name = "Jeong Yo Han" };
    }

    public class DataObject : INotifyPropertyChanged
    {
        private string _name;
        public string name
        {
            get { return _name; }
            set {
                _name = value;
                onPropertyChanged("name");
            }
        }
        public event PropertyChangedEventHandler PropertyChanged;
        public void onPropertyChanged(string name)
        {
            if (PropertyChanged != null)
                PropertyChanged(this, new PropertyChangedEventArgs(name));
        }
    }  

In my MainWindow Page, I declared my custom control Tag

<Grid>
    <cc:CustomControl1 Background="Red" 
                       Textaa="{Binding name ,Mode=TwoWay, UpdateSourceTrigger=PropertyChanged}" >
    </cc:CustomControl1>
</Grid>

I tried to test that does templatedParent in Template Style works for two-way binding. ( see a RelativeSource= { Rela ... TemplatedParent } ).

and I run my program to see when I get hit name setter property in DataObject class. even I add UpdateSourceTrigger=PropertyChanged, but It doesn't work well when I change text in my TextBox. It works when I lost focus on it, Even I typed UpdateSourceTrigger=PropertyChanged.

So I Changed my source Like following source.

<!-- in Generic.xaml (Template style) -->
<TextBox Background="{TemplateBinding Background}" 
                           Text="{Binding Textaa, 
                           UpdateSourceTrigger=PropertyChanged,
                                 RelativeSource={RelativeSource TemplatedParent}}">
</TextBox>
<!--- in MainWindow.xaml--->
<cc:CustomControl1 Background="Red" 
                       Textaa="{Binding name ,Mode=TwoWay}" >
 </cc:CustomControl1>

this works well, as I expected.
and following is not working, Not I expected.

<!-- in Generic.xaml (Template style) -->
<TextBox Background="{TemplateBinding Background}" 
                           Text="{Binding Textaa, 
                           UpdateSourceTrigger=PropertyChanged, Mode=TwoWay,
                                 RelativeSource={RelativeSource TemplatedParent}}">
</TextBox>
<!--- in MainWindow.xaml--->
<cc:CustomControl1 Background="Red" 
                       Textaa="{Binding name}" >
 </cc:CustomControl1>

But I'm Confusing that why I should put UpdateSourceTrigger Option to StyleTemplate and Mode= TwoWayBinding Option to directly Textaa dependency property of customcontrol tag.

I need an explanation. Thank you for reading.

for helping your understand I added my reop for my source, below.

click here to see entire source

Answer 1

The default behavior for updating the source property of a Binding of the Text property of a TextBox is LostFocus .

See the Remarks on the TextBox.Text Property page:

When used in data-binding scenarios, this property uses the default update behavior of UpdateSourceTrigger.LostFocus.

You do however not need to set Mode=TwoWay , because that is already the default. So the TextBox declaration should look like this:

<TextBox Background="{TemplateBinding Background}" 
         Text="{Binding Textaa,
                UpdateSourceTrigger=PropertyChanged,
                RelativeSource={RelativeSource TemplatedParent}}" />

---

It is not necessary to set UpdateSourceTrigger=PropertyChanged on the Binding of your Textaa property, because (in contrast to TextBlock.Text ), the default behaviour of your custom dependency property is already PropertyChanged .

You may also register your property in a way that makes it bind two-way by default, so that you would not have to set Mode=TwoWay on the Textaa Binding:

public static readonly DependencyProperty TextaaProperty =
    DependencyProperty.Register(
        nameof(Textaa), typeof(string), typeof(CustomControl1),
        new FrameworkPropertyMetadata(
            null, FrameworkPropertyMetadataOptions.BindsTwoWayByDefault));

Now you can bind the Textaa property like this:

<cc:CustomControl1 Textaa="{Binding name}" />