使用谓词绑定在命令上的搜索栏不起作用。 Xamarin.Forms

Question

After such a binding, it is impossible to focus on the search bar. When tapped nothing happens. After calling ChangeCanExecute() SearchBar's property IsEnabled changes to true and that's all.

Can't figure out where the error is.

Xamarin.Forms version: 4.8.0.1451

.NET Standard 2.1

My view:

<ContentPage xmlns="http://xamarin.com/schemas/2014/forms"
             xmlns:x="http://schemas.microsoft.com/winfx/2009/xaml"
             xmlns:local="clr-namespace:SearchBarTest"
             x:Class="SearchBarTest.MainPage">
    <ContentPage.BindingContext>
        <local:TestViewModel/>
    </ContentPage.BindingContext>
    <StackLayout>
        <SearchBar SearchCommand="{Binding TestCommand}"/>
    </StackLayout>
</ContentPage>

View model:

internal class TestViewModel
{
    private bool isInitialized;

    public Command TestCommand { get; }

    public TestViewModel()
    {
        Task.Run(() =>
        {
            Thread.Sleep(5000);

            isInitialized = true;

            Debug.WriteLine($">>> Initialized: {isInitialized}");

            TestCommand.ChangeCanExecute();
        });

        TestCommand = new Command(() =>
        {
            Debug.WriteLine(">>> Command invoked.");
        }, () => isInitialized);
    }
}

Answer 1

You need to click the Search Icon from Input Keyboard , then the SearchCommand will be invoked.

Then the output:

12-31 11:20:29.425 I/AssistStructure(31728): Flattened final assist data: 2560 bytes, containing 1 windows, 9 views
[0:] >>> Command invoked.

==========================update===============================

I have checked the sample, the problem has been found. You add Thread.Sleep(5000) in the Task thread. It will make the isInitialized = true later than invoke TestCommand code.

Therefore , TestCommand can not be executed all the time.

The solution that you need to comment this line code Thread.Sleep(5000) .

...
public TestViewModel()
{
    Task.Run(() =>
    {
        //Thread.Sleep(5000);

        isInitialized = true;

        Debug.WriteLine($">>> Initialized: {isInitialized}");

        TestCommand.ChangeCanExecute();
    });

    TestCommand = new Command(() =>
    {
        Debug.WriteLine(">>> Command invoked.");
    }, () => isInitialized);
}
...