Xaml Can'；t绑定IsBusy属性

我有一个带有以下代码的活动指示器的页面：

<?xml version="1.0" encoding="utf-8" ?>
<ContentPage xmlns="http://xamarin.com/schemas/2014/forms"
             xmlns:x="http://schemas.microsoft.com/winfx/2009/xaml"
             x:Class="MyApp.ClientSearch" Title="Search">
  <ContentPage.Content>
    <StackLayout Orientation="Vertical">
      <StackLayout.Children>
        <SearchBar x:Name="txtSearchClient" TextChanged="OnTextChanged"></SearchBar>
        <ActivityIndicator IsVisible="{Binding IsBusy}" IsRunning="{Binding IsBusy}" x:Name="indicadorCargando" />
        <ListView x:Name="lstClients"></ListView>
      </StackLayout.Children>
    </StackLayout>  
  </ContentPage.Content>
</ContentPage>

如您所见，

this.IsBusy

正在设置页面属性，因此尝试绑定到XAML中的该属性。不幸的是，它不起作用：

<ActivityIndicator IsVisible="{Binding IsBusy}" IsRunning="{Binding IsBusy}" x:Name="indicadorCargando" />

---

但我不想这样做，我想设置一个值而不是三个值。

下面是我将如何重写它：

public class ClientSearch : ContentPage
    {
        public ClientSearch()
        {
            BindingContext = new ClientSearchViewModel();
            var stack = new StackLayout();
            var searchBar = new SearchBar();
            searchBar.SetBinding<ClientSearchViewModel>(SearchBar.TextProperty, x => x.Text);
            var actInd = new ActivityIndicator();
            actInd.SetBinding<ClientSearchViewModel>(ActivityIndicator.IsVisibleProperty, x => x.IsBusy);
            actInd.SetBinding<ClientSearchViewModel>(ActivityIndicator.IsRunningProperty, x => x.IsBusy);
            var lv = new ListView
            {
                ItemTemplate = new DataTemplate(() =>
                {
                    var txtCell = new TextCell();
                    txtCell.SetBinding<MyItemModel>(TextCell.TextProperty, x => x.Name_Ct);
                    txtCell.SetBinding<MyItemModel>(TextCell.TextProperty, x => x.Cod_Ct);
                    return txtCell;
                })
            };
            lv.SetBinding<ClientSearchViewModel>(ListView.ItemsSourceProperty, x => x.items);
            stack.Children.Add(searchBar);
            stack.Children.Add(actInd);
            stack.Children.Add(lv);
            Content = stack;
        }
    }

    public class ClientSearchViewModel : BaseViewModel
    {
        public string Text { get; set; }
        public bool IsBusy { get; set; }
        public IEnumerable<MyItemModel> items { get; set; }

        protected override async void OnPropertyChanged(string propertyName = null)
        {
            if (propertyName != nameof(Text) || Text.Length < 3) return;
            IsBusy = true;
            items = await App.ClientsManager.GetTasksAsync(Text);
            IsBusy = false;
        }
    }

    [ImplementPropertyChanged]
    public abstract class BaseViewModel : INotifyPropertyChanged
    {
        public event PropertyChangedEventHandler PropertyChanged;

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

public类ClientSearch:ContentPage
{
公共客户端搜索（）
{
BindingContext=new ClientSearchViewModel（）；
var stack=新的StackLayout（）；
var searchBar=新的searchBar（）；
searchBar.SetBinding（searchBar.TextProperty，x=>x.Text）；
var actInd=新的ActivityIndicator（）；
actInd.SetBinding（ActivityIndicator.IsVisibleProperty，x=>x.IsBusy）；
actInd.SetBinding（ActivityIndicator.isRunning属性，x=>x.IsBusy）；
var lv=新列表视图
{
ItemTemplate=新数据模板（（）=>
{
var txtCell=新的TextCell（）；
txtCell.SetBinding（TextCell.TextProperty，x=>x.Name\u Ct）；
txtCell.SetBinding（TextCell.TextProperty，x=>x.Cod\u Ct）；
返回txtCell；
})
};
lv.SetBinding（ListView.ItemsSourceProperty，x=>x.items）；
stack.Children.Add（搜索栏）；
stack.Children.Add（actInd）；
stack.Children.Add（lv）；
内容=堆栈；
}
}
公共类ClientSearchViewModel:BaseViewModel
{
公共字符串文本{get；set；}
公共bool正忙{get；set；}
公共IEnumerable项{get；set；}
受保护的重写异步无效OnPropertyChanged（字符串propertyName=null）
{
if（propertyName！=nameof（Text）| | Text.Length<3）返回；
IsBusy=true；
items=wait App.ClientsManager.GetTasksAsync（文本）；
IsBusy=false；
}
}
[实现属性更改]
公共抽象类BaseViewModel:INotifyPropertyChanged
{
公共事件属性更改事件处理程序属性更改；
受保护的虚拟无效OnPropertyChanged（[CallerMemberName]string propertyName=null）=>PropertyChanged？.Invoke（这是新的PropertyChangedEventArgs（propertyName））；
}

您当然可以选择独立视图模型，这是个不错的主意。但是对于特定的问题，看起来您并没有在任何地方设置BindingContext，因此它不会得到您想要的IsBusy属性

我还没有尝试将控件的BindingContext设置为自身，但类似的方法应该可以工作：

<ActivityIndicator
  IsVisible="{Binding IsBusy}"
  IsRunning="{Binding IsBusy}"
  x:Name="indicadorCargando"
  BindingContext="{x:Reference indicadorCargando}" />

您需要为页面指定一个名称（

x:name=“myPage”

），然后使用

{binding Source={x:reference myPage}，Path=IsBusy}

对ActivityIndicator的

IsVisible

和

IsRunning

值的引用来声明绑定。关于.< /p> 1的更多信息-为了清晰2，你应该考虑分离视图和视图模型——你应该在XAML 3中添加文本单元——你应该使用E文本。

public class ClientSearch : ContentPage
    {
        public ClientSearch()
        {
            BindingContext = new ClientSearchViewModel();
            var stack = new StackLayout();
            var searchBar = new SearchBar();
            searchBar.SetBinding<ClientSearchViewModel>(SearchBar.TextProperty, x => x.Text);
            var actInd = new ActivityIndicator();
            actInd.SetBinding<ClientSearchViewModel>(ActivityIndicator.IsVisibleProperty, x => x.IsBusy);
            actInd.SetBinding<ClientSearchViewModel>(ActivityIndicator.IsRunningProperty, x => x.IsBusy);
            var lv = new ListView
            {
                ItemTemplate = new DataTemplate(() =>
                {
                    var txtCell = new TextCell();
                    txtCell.SetBinding<MyItemModel>(TextCell.TextProperty, x => x.Name_Ct);
                    txtCell.SetBinding<MyItemModel>(TextCell.TextProperty, x => x.Cod_Ct);
                    return txtCell;
                })
            };
            lv.SetBinding<ClientSearchViewModel>(ListView.ItemsSourceProperty, x => x.items);
            stack.Children.Add(searchBar);
            stack.Children.Add(actInd);
            stack.Children.Add(lv);
            Content = stack;
        }
    }

    public class ClientSearchViewModel : BaseViewModel
    {
        public string Text { get; set; }
        public bool IsBusy { get; set; }
        public IEnumerable<MyItemModel> items { get; set; }

        protected override async void OnPropertyChanged(string propertyName = null)
        {
            if (propertyName != nameof(Text) || Text.Length < 3) return;
            IsBusy = true;
            items = await App.ClientsManager.GetTasksAsync(Text);
            IsBusy = false;
        }
    }

    [ImplementPropertyChanged]
    public abstract class BaseViewModel : INotifyPropertyChanged
    {
        public event PropertyChangedEventHandler PropertyChanged;

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

<ActivityIndicator
  IsVisible="{Binding IsBusy}"
  IsRunning="{Binding IsBusy}"
  x:Name="indicadorCargando"
  BindingContext="{x:Reference indicadorCargando}" />