Csharp Xamarin：ImageButton 未从样式设置器调用命令

我的理解是，您的目标是让自定义NavigationHeader中的back按钮调用App类中的OnBackButtonPressed方法:

public partial class App : Application
{
    public async void OnBackButtonPressed(object sender, EventArgs e)
    {
        // This pop up will be the test.
        await MainPage.DisplayAlert("Message from button", "It worked", "OK");
    }
}

我已经测试了Download from GitHub种方法来实现您想要的结果，其中考虑了您的自定义NavigationHeader在某种视图中被消费的可能性(例如ContentPage).

try 在样式声明中进行以下更改:

<Setter Property="Command" Value="{Binding BackButtonPressedCommand}" />

这样，当您使用自定义NavigationHeader时，例如在您的MainPage.xaml...

<ContentPage xmlns="http://xamarin.com/schemas/2014/forms"
         xmlns:x="http://schemas.microsoft.com/winfx/2009/xaml"
         xmlns:custom_back_button="clr-namespace:custom_back_button"
         x:Class="custom_back_button.MainPage">

<StackLayout>
    <custom_back_button:HeaderNavigation  VerticalOptions="CenterAndExpand"/>
</StackLayout>

...绑定命令将在主页的上下文中调用.(同样，如果在大约other页上使用它，它将吸收that页的BindingContext.)

public partial class MainPage : ContentPage
{
    public MainPage()
    {
        BindingContext = new MainPageBinding();
        InitializeComponent();
    }
}

在BindingContext中解析ICommand，从而调用this类中的OnBackButtonPressed.现在使用((App)Application.Current)将操作传递给App类，如图所示.

class MainPageBinding
{
    public MainPageBinding()
    {
        BackButtonPressedCommand = new Command(OnBackButtonPressed);
    }

    public ICommand BackButtonPressedCommand { get; private set; }
    private void OnBackButtonPressed(object o)
    {
        ((App)Application.Current).OnBackButtonPressed(o, EventArgs.Empty);
    }
}

按下后退按钮显示成功调用编码为App.OnBackButtonPressed的弹出窗口.