Xamarin forms 从列表中设置选择器 SelectedItem

Question

我正在使用Xamarin.Forms并且我正在使用Picker作为下拉列表。

我正在尝试让 Picker 显示与ViewModel中的ObservableCollection中的字符串（为了简化目的）匹配的书名。

PageOne.xaml：

<Picker x:Name="BookPicker" ItemDisplayBinding="{Binding Name}" ItemsSource="{Binding BookTypeList}"></Picker>

PageOne.cs：

public PageOne()
{
     InitializeComponent();
     this.BindingContext = new BookViewModel();

     string myBook = "c";

     for (int x = 0; x < 5; x++)
     {
          if (BookViewModel.BookTypeList[x].Name == myBook)
          {
               BookPicker.SelectedIndex = x;
          } 
     }
}

书视图模型：

  public BookViewModel()
    {
        BookTypeList = new ObservableCollection<BookType>(){
            new BookType() { BookID = 0, Name = "a" },
            new BookType() { BookID = 1, Name = "b" },
            new BookType() { BookID = 2, Name = "c" },
            new BookType() { BookID = 3, Name = "d" },
            new BookType() { BookID = 4, Name = "e" },
        };
        bookType = BookTypeList[0];
    }

    public class BookType
    {
        public int BookID { get; set; }
        public string Name { get; set; }
    }

BookViewModel.BookTypeList导致此错误：

CS0120：非静态字段、方法或属性需要 object 引用

如何遍历 BookViewModel 中的ObservableCollection以找到与字符串匹配的 ID，以便设置 Picker.SelectedIndex？

谢谢！

Answer 1

您收到该错误是因为BookViewModel不是 static class，如果您要访问BookTypeList ，您需要通过BookViewModel实例进行操作

public PageOne()
{
     InitializeComponent();
     this.BindingContext = new BookViewModel();

     string myBook = "c";
     var vm = BindingContext as BookViewModel;
     for (int x = 0; x < 5; x++)
     {
          if (vm.BookTypeList[x].Name == myBook)
          {
               BookPicker.SelectedIndex = x;
          } 
     }
}

此外，如果您在 ObservableCollection 中有一个独特的项目，您可以用FindIndex替换您的 For 循环：

public PageOne()
{
     InitializeComponent();
     this.BindingContext = new BookViewModel();

     string myBook = "c";
     var vm = BindingContext as BookViewModel;
     BookPicker.SelectedIndex = vm.BookTypeList.FindIndex(x => x.Name.Equals(myBook));
}

或SelectedItem而不是SelectedIndex

 BookPicker.SelectedItem = vm.BookTypeList.Find(x => x.Name.Equals(myBook));

如果项目不是唯一的，您可能需要使用Linq中的Where子句/扩展方法