MvvmCross binding 属性 自定义类型到自定义视图

Question

我尝试在 View Model 中使用自定义 View 绑定 属性 自定义类型，但在 Binder 方法中 "SetValue(object value)" 值始终为 null。为什么会这样？是否无法在 MvvmCross 中将自定义类型 属性 与自定义视图绑定？

我的视图模型：

public class RecipesFiltersVM : MvxViewModel
{
    public SearchField DishField { get; private set; }
    public SearchField CuisineField { get; private set; }
    public SearchField IngredientField { get; private set; }

    private readonly IFiltersService _filtersService;

    public RecipesFiltersVM(IFiltersService filtersService)
    {
        _filtersService = filtersService;

        UpdateSearchFields ();
    }

    private async void UpdateSearchFields ()
    {
        var allFilters = await _filtersService.LoadAllFilters ();

        DishField = new SearchField (
            allFilters
            .Where(f => f.Type == FilterType.Dish)
            .ToList()
        );
        CuisineField = new SearchField (
            allFilters
            .Where(f => f.Type == FilterType.Cuisine)
            .ToList()
        );
        IngredientField = new SearchField (
            allFilters
            .Where(f => f.Type == FilterType.Ingredient)
            .ToList()
        );
    }
}

我的搜索字段：

public class SearchField : MvxViewModel
{
    private String _searchResult;
    public String SearchResult {
        get { return _searchResult; }
        set {
            _searchResult = value;
            RaisePropertyChanged (() => SearchResult);
            UpdateFoundFilters ();
        }
    }

    private ObservableCollection<Filter> _foundFilters;
    public ObservableCollection<Filter> FoundFilters {
        get { return _foundFilters; }
        set {
            _foundFilters = value;
            RaisePropertyChanged (() => FoundFilters);
        }
    }
}

在自定义视图中：

public class SearchFieldView : UIView
{
    public UITextField SearchResult { get { return _searchResult; } }
    private UITextField _searchResult;

    public UITableView FoundFilters { get { return _foundFilters; } }
    private UITableView _foundFilters;
}

活页夹中：

public class SearchFieldViewWithSearchFieldBinder : MvxTargetBinding
{
    protected SearchFieldView SearchFieldView {
        get { return (SearchFieldView)Target; }
    }

    public SearchFieldViewWithSearchFieldBinder (SearchFieldView target)
        : base (target)
    {

    }

    public override void SetValue (object value)
    {
        //value is always null!
    }

    public override Type TargetType {
        get
        {
            return typeof(SearchField);
        }
    }

    public override MvxBindingMode DefaultMode {
        get
        {
            return MvxBindingMode.TwoWay;
        }
    }
}

设置：

protected override void FillTargetFactories (Cirrious.MvvmCross.Binding.Bindings.Target.Construction.IMvxTargetBindingFactoryRegistry registry)
    {
        registry.RegisterCustomBindingFactory<SearchFieldView> (
            "SearchField",
            indicators => new SearchFieldViewWithSearchFieldBinder(indicators)
        );
        base.FillTargetFactories (registry);
    }

在ViewController中：

var set = this.CreateBindingSet<RecipesFiltersDialog, RecipesFiltersVM>();
set.Bind (_dish).For("SearchField").To (vm => vm.DishField);
set.Bind (_cuisine).For("SearchField").To (vm => vm.CuisineField);
set.Bind (_ingredient).For("SearchField").To (vm => vm.IngredientField);
set.Apply ();

UPD

通过两种方式解决了更新 ViewModel 代码的问题。首先，我更改了自定义 属性 声明，例如：

private SearchField _dishField;
    public SearchField DishField {
        get
        {
            return _dishField;
        }
        set
        {
            _dishField = value;
            RaisePropertyChanged (() => DishField);
        }
    }

其次，我在 UpdateSearchFields () 执行之前在 ViewModel 构造函数中初始化我的属性：

public RecipesFiltersVM(IFiltersService filtersService)
    {
        _filtersService = filtersService;

        DishField = new SearchField (new List<Filter> ());
        CuisineField = new SearchField (new List<Filter> ());
        IngredientField = new SearchField (new List<Filter> ());

        UpdateSearchFields ();
    }

Answer 1

您需要为自定义视图创建自己的自定义绑定。例如，如果您遵循了使用 public C# 属性和 C# 事件来定义自定义视图中的项的常规 MvvmCross 实践，那么您应该能够执行如下操作：

public class SearchFieldView : UIView, IMvxBindable
{
    public IMvxBindingContext BindingContext { get; set; }

    public SearchFieldView()
    {
         this.CreateBindingContext();
    }

    public UITextField SearchResult { get { return _searchResult; } }
    private UITextField _searchResult;

    public UITableView FoundFilters { get { return _foundFilters; } }
    private UITableView _foundFilters;

    [MvxSetToNullAfterBinding]
    public object DataContext
    {
        get { return BindingContext.DataContext; }
        set { BindingContext.DataContext = value; }
    }

    protected override void Dispose(bool disposing)
    {
        if (disposing)
        {
            BindingContext.ClearAllBindings();
        }
        base.Dispose(disposing);
    }
}

然后它应该只是 "work." 为了获得灵感，检查诸如 MvxView or MvxTableViewCell.

之类的东西

---

或者，您可以像 MvvmCross 处理 UISegmentedControlBindings 的方式那样通过实现 MvxUISegmentedControlSelectedSegmentTargetBinding.

Answer 2

解决了 注释以两种方式更新 ViewModel 代码。首先，我更改了自定义 属性 声明，例如：

private SearchField _dishField;
    public SearchField DishField {
        get
        {
            return _dishField;
        }
        set
        {
            _dishField = value;
            RaisePropertyChanged (() => DishField);
        }
    }

其次，我在 UpdateSearchFields () 执行之前在 ViewModel 构造函数中初始化我的属性：

public RecipesFiltersVM(IFiltersService filtersService)
    {
        _filtersService = filtersService;

        DishField = new SearchField (new List<Filter> ());
        CuisineField = new SearchField (new List<Filter> ());
        IngredientField = new SearchField (new List<Filter> ());

        UpdateSearchFields ();
    }