Question

我有这个XAML代码：

<StackLayout Grid.Row="0" Grid.Column="0" Padding="15,10,20,10" HorizontalOptions="StartAndExpand" VerticalOptions="CenterAndExpand">
   <StackLayout.GestureRecognizers>
      <TapGestureRecognizer Tapped="tapFavorites" NumberOfTapsRequired="1" />
   </StackLayout.GestureRecognizers>
   <Label x:Name="faveLabel" FontFamily="FontAwesome" XAlign="Center" FontSize="23">
      <Label.Triggers>
         <DataTrigger TargetType="Label" Binding="{Binding Favorite}" Value="true">
            <Setter Property="TextColor" Value="Red" />
         </DataTrigger>
         <DataTrigger TargetType="Label" Binding="{Binding Favorite}" Value="false">
            <Setter Property="TextColor" Value="Gray" />
         </DataTrigger>
      </Label.Triggers>
   </Label>
</StackLayout>

在我的C＃代码中，我很熟悉设置标签的Text属性，只需指定如下：

sampleLabel.Text = "ABC"

但这种情况不同。有人可以告诉我如何在点击标签时从C＃更改标签的颜色。

Answer 1

这个怎么样：

<强>的MainPage：

public partial class MainPage : ContentPage
{
    MyViewModel vm;

    public MainPage()
    {
        InitializeComponent();

        vm = new MyViewModel();
        BindingContext = vm;

        var faveLabel = new Label { FontSize = 24, FontFamily = "FontAwesome", Text = "Tap Here !" };

        var trigger1 = new DataTrigger(typeof(Label));
        trigger1.Binding = new Binding("Favorite", BindingMode.TwoWay);
        trigger1.Value = true;
        trigger1.Setters.Add(new Setter { Property = Label.TextColorProperty, Value = Color.Red });

        var trigger2 = new DataTrigger(typeof(Label));
        trigger2.Binding = new Binding("Favorite", BindingMode.TwoWay);
        trigger2.Value = false;
        trigger2.Setters.Add(new Setter { Property = Label.TextColorProperty, Value = Color.Gray });

        faveLabel.Triggers.Add(trigger1);
        faveLabel.Triggers.Add(trigger2);

        var sl = new StackLayout {
            HorizontalOptions = LayoutOptions.StartAndExpand,
            VerticalOptions = LayoutOptions.CenterAndExpand
        };

        var tgr = new TapGestureRecognizer();
        tgr.NumberOfTapsRequired = 1;
        tgr.Tapped += tapFavorites;
        sl.GestureRecognizers.Add(tgr);

        sl.Children.Add(faveLabel);

        Content = sl;
    }

    public void tapFavorites(object sender, EventArgs e)
    {
        vm.Favorite = !vm.Favorite;
    }
}

<强>视图模型：

public class MyViewModel : INotifyPropertyChanged
{
    public event PropertyChangedEventHandler PropertyChanged;

    private bool favorite;
    public bool Favorite
    {
        get { return favorite; }
        set
        {
            if (value != favorite)
            {
                favorite = value;
                NotifyPropertyChanged();
            }
        }
    }
    private void NotifyPropertyChanged([CallerMemberName] String propertyName = "")
    {
        PropertyChanged?.Invoke(this, new PropertyChangedEventArgs(propertyName));
    }
}

Answer 2

您可以通过它的名称和GestureRecognizer访问您的faveLabel。在那里，您将标签的TextColor设置为另一个。除了在箭头功能之后输入代码，您还可以提供功能。

faveLabel.GestureRecognizers.Add( new TapGestureRecognizer { Command = new Command( () => faveLabel.TextColor = Color.Red ) });

除了在箭头功能之后输入完整代码，您还可以提供功能。

... { Command = new Command(() => OnLabelClicked() ) }

Here是（Tap）GestureRecognizers的官方Xamarin文档的链接。

Answer 3

如果您在xaml中执行操作，那么触发器就是可行的方法，但如果您在代码中执行此操作，则无论使用哪种方式都可以执行此操作 - 使用或不使用触发器

您可以在模型中保留收藏夹和/或标签文本颜色并进行绑定。如果您有模型，那么您也可以绑定tapFavorites，如Marimba所示

public partial class MainPage : ContentPage
{
    Label faveLabel;
    bool favorite = false;

    public MainPage()
    {
        InitializeComponent();

        faveLabel = new Label { FontSize = 24, FontFamily = "FontAwesome", Text = "Tap Here !" };

        var sl = new StackLayout {
            HorizontalOptions = LayoutOptions.StartAndExpand,
            VerticalOptions = LayoutOptions.CenterAndExpand
        };

        var tgr = new TapGestureRecognizer();
        tgr.NumberOfTapsRequired = 1;
        tgr.Tapped += tapFavorites;
        sl.GestureRecognizers.Add(tgr);

        sl.Children.Add(faveLabel);

        Content = sl;
    }

    public void tapFavorites(object sender, EventArgs e)
    {
        favorite = ! favorite;
        faveLabel.TextColor = favorite ? Color.Red : Color.Gray;
    }
}

仅在C＃中更改Xamarin表单标签的颜色，没有XAML

3 个答案: