您应该这样使用 ActivityIndi​​cator

<ActivityIndicator AbsoluteLayout.LayoutBounds="0, 0, 1, 1"
                               AbsoluteLayout.LayoutFlags="All"
                               IsVisible="{Binding IsBusy}" 
                               IsRunning="{Binding IsBusy}" 
                               Color="{StaticResource PrimaryColor}"
                               VerticalOptions="Center"
                               HorizontalOptions="Center" />

对 IsRunning 属性c> IsBusy 属性

Use IsRunning property with IsBusy property

    private bool _isBusy;

    public bool IsBusy
    {
        get
        {
            return _isBusy;
        }

        set
        {
            _isBusy = value;
            RaisePropertyChanged(() => IsBusy);
        }
    }

在视图模型中

  class GalleryViewModel : ExtendedBindableObject 
{
...
     private async Task DoGetImagesCommand(string pCode, string gCode, string gUrl)
    {
        IsBusy = true;
        var images = await _galleryService.GetImageList(pCode, gCode, gUrl);
        foreach (var image in images)
            Galleries.Add(image);
        IsBusy = false;
    }
}

在另一个班级

public abstract class ExtendedBindableObject : BindableObject
    {
        public void RaisePropertyChanged<T>(Expression<Func<T>> property)
        {
            var name = GetMemberInfo(property).Name;
            OnPropertyChanged(name);
        }

        private MemberInfo GetMemberInfo(Expression expression)
        {
            MemberExpression operand;
            LambdaExpression lambdaExpression = (LambdaExpression)expression;
            if (lambdaExpression.Body is UnaryExpression)
            {
                UnaryExpression body = (UnaryExpression)lambdaExpression.Body;
                operand = (MemberExpression)body.Operand;
            }
            else
            {
                operand = (MemberExpression)lambdaExpression.Body;
            }
            return operand.Member;
        }
    }