CrossFAB组件绑定Command报错及空引用问题求助

Let's break down your issues step by step and fix them one by one:

First Error: No property, bindable property, or event found for 'OnClickCommand' #

This error happens because the OnClickCommand property on FloatingButton isn't defined as a BindableProperty—only BindableProperties work with XAML bindings like {Binding}. Here's how to fix the component:

1. Open the FloatingButton.xaml.cs file from the CrossFAB component.
2. Add a BindableProperty definition for OnClickCommand (if it doesn't already exist):

public static readonly BindableProperty OnClickCommandProperty =
    BindableProperty.Create(
        nameof(OnClickCommand),
        typeof(ICommand),
        typeof(FloatingButton),
        null);

public ICommand OnClickCommand
{
    get => (ICommand)GetValue(OnClickCommandProperty);
    set => SetValue(OnClickCommandProperty, value);
}

3. Update the button's tap/click handler to safely trigger the command (to prevent future null references):

private void OnButtonTapped(object sender, EventArgs e)
{
    // Always check if the command exists and can execute before calling Execute
    if (OnClickCommand != null && OnClickCommand.CanExecute(null))
    {
        OnClickCommand.Execute(null);
    }
}

Second Error: Object reference not set to an instance of an object #

This occurs because your btnPage2Command is initialized after XAML bindings are resolved (during InitializeComponent()), and your page doesn't notify the binding of the update. Choose one of these two fixes:

Option 1: Initialize the command before loading XAML

Move command initialization to the start of your page's constructor so it exists when the XAML parses bindings:

public page1()
{
    // Initialize command first
    btnPage2Command = new Command(OpenPage2);
    // Then load the XAML
    InitializeComponent();
    // Set the page as its own binding context
    BindingContext = this;
}

Option 2: Implement INotifyPropertyChanged

If you prefer initializing the command after InitializeComponent(), implement this interface to notify the binding when the command is set:

public partial class page1 : ContentPage, INotifyPropertyChanged
{
    private ICommand _btnPage2Command;
    public ICommand btnPage2Command
    {
        get => _btnPage2Command;
        set
        {
            _btnPage2Command = value;
            OnPropertyChanged();
        }
    }

    public page1()
    {
        InitializeComponent();
        BindingContext = this;
        btnPage2Command = new Command(OpenPage2);
    }

    public event PropertyChangedEventHandler PropertyChanged;

    protected virtual void OnPropertyChanged([CallerMemberName] string propertyName = null)
    {
        PropertyChanged?.Invoke(this, new PropertyChangedEventArgs(propertyName));
    }

    private async void OpenPage2()
    {
        await Application.Current.MainPage.Navigation.PushAsync(new page2());
    }
}

Extra Reliability Tip #

To avoid BindingContext confusion, explicitly target your page in the XAML binding:

<c:FloatingButton 
    x:Name="page1" 
    BGColor="#59E1FF" 
    IconSrc="page1" 
    OnClickCommand="{Binding btnPage2Command, Source={RelativeSource AncestorType={x:Type local:page1}}}" />

Just add your app's namespace to the top of the XAML file first:

xmlns:local="clr-namespace:YourAppNamespaceHere"

内容的提问来源于stack exchange，提问作者A. Vreeswijk