MVVM 搜索栏 Xamarin.Forms

Question

我正在尝试在 Xamarin.forms 中使用 MVVM 实现搜索栏。到目前为止，我已经设法从互联网上借用了一些代码，它似乎确实经历了搜索的过程。唯一的问题是我不知道在命令中输入什么代码。

我希望搜索栏从食谱列表中搜索食谱名称。这些信息都存储在本地数据库中，并使用可观察的集合显示。

请你帮我解决一下。

XAML

<SearchBar x:Name="SearchBar" 
               Placeholder="Search" 
               SearchCommand="{Binding SearchCommand}" 
               SearchCommandParameter="{Binding Text, Source={x:Reference SearchBar}}"
               Text="{Binding SearchText, Mode=TwoWay}">
        <SearchBar.Behaviors>
            <local:TextChangedBehavior />
        </SearchBar.Behaviors>
    </SearchBar>
    <ListView x:Name="ListViewItems"
          ItemsSource="{Binding Recipes}"
          IsPullToRefreshEnabled="True"
          Refreshing="ListViewItems_Refreshing"
          SelectedItem="{Binding SelectedRecipe}">

文字改变了行为

    class TextChangedBehavior: Behavior<Xamarin.Forms.SearchBar>
{
    protected override void OnAttachedTo(Xamarin.Forms.SearchBar bindable)
        {
            base.OnAttachedTo(bindable);
            bindable.TextChanged += Bindable_TextChanged;
        }

        protected override void OnDetachingFrom(Xamarin.Forms.SearchBar bindable)
        {
            base.OnDetachingFrom(bindable);
            bindable.TextChanged -= Bindable_TextChanged;
        }

        private void Bindable_TextChanged(object sender, TextChangedEventArgs e)
        {
            ((Xamarin.Forms.SearchBar)sender).SearchCommand?.Execute(e.NewTextValue);
        }

    }

和视图模型

public class RecipeListViewModel : ObservableCollection<Recipe>
{
    private ObservableCollection<Recipe> Recipes {get; set;}
    public INavigation Navigation { get; internal set; }
    public ICommand NewAddPage { get; protected set; }
    public RecipeListViewModel(INavigation navigation)
    {
        this.Navigation = navigation;
        Recipes = new ObservableCollection<Recipe>();
        this.NewAddPage = new Command(async () => await CreateNewAddPage());
        Init();
    }

    // Gets all recipes from the database and adds them to the observable collection
    private void Init()
    {
        var enumarator = App.RecipeDbcontroller.GetRecipe();
        if (enumarator == null)
        {
            App.RecipeDbcontroller.SaveRecipe(new Recipe { RecipeName = "Moussaka", Serves = 6, PrepTime = "30", CookTime = "2 Hours", MealType = "Dinner" });

            enumarator = App.RecipeDbcontroller.GetRecipe();
        }
        while (enumarator.MoveNext())
        {
            //cleans database of all empty records
            if (enumarator.Current.RecipeName == null || enumarator.Current.CookTime == null)
            {
                App.RecipeDbcontroller.DeleteRecipe(enumarator.Current.RecipeID);
            }
            else
                Add(enumarator.Current);
        }
    }


    private ICommand _searchCommand;
    public ICommand SearchCommand
    {
        get
        {
            return _searchCommand ?? (_searchCommand = new Command<string>((text) =>
            {
                **// THIS IS WHAT I DON'T KNOW WHAT TO DO**
            }));
        }
    }

    private string _searchText { get; set; }
    public string SearchText
    {
        get { return _searchText; }
        set
        {
            if (_searchText != value)
            {
                _searchText = value;
            }
            OnPropertyChanged();
        }
    }

    public event PropertyChangedEventHandler PropertyChanged;

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

RecipeDatabaseController 类

 public RecipeDatabaseController()
        {
            this.database = DependencyService.Get<ISQLite>().GetConnection();
            this.database.CreateTable<Recipe>();
        }

        //Recipe CRUD
        public IEnumerator<Recipe> GetRecipe()
        {
            lock (locker)
            {
                if (database.Table<Recipe>().Count() == 0)
                {
                    return null;
                }
                else
                {
                    return this.database.Table<Recipe>().GetEnumerator();
                }
            }
        }

        public IEnumerator<Recipe> GetRecipeBySearchTerm(text)
        {
            var enumarator = GetRecipe();
            lock (locker)
            {
                while (enumarator.MoveNext)
                {
                    if(enumarator.Current.RecipeName.Contains(text)
                        return this.
                }
            }
        }

        public int SaveRecipe(Recipe recipe)
        {
            lock (locker)
            {
                if (recipe.RecipeID != 0)
                {
                    this.database.Update(recipe);
                    return recipe.RecipeID;
                }
                else
                {
                    return this.database.Insert(recipe);
                }
            }
        }

        public int DeleteRecipe(int Id)
        {
            lock (locker)
            {
                return this.database.Delete<Recipe>(Id);
            }
        }

Answer 1

正确，所以搜索命令应该是这样的。

public ICommand SearchCommand => _searchCommand ?? (_searchCommand = new Command<string>((text) =>
{
    if (text.Length >=1)
    {
        Recipes.Clear();
        Init();
        var suggestions = Recipes.Where(c => c.RecipeName.ToLower().StartsWith(text.ToLower())).ToList();
        Recipes.Clear();
        foreach (var recipe in suggestions)
         Recipes.Add(recipe);

    }
    else
    {
        Recipes.Clear();
        Init();
        ListViewVisible = true;
        SuggestionsListViewVisible = false;
    }

}));

Answer 2

using System.Linq;

    //Recipe CRUD
    public IEnumerable<Recipe> GetRecipe()
    {
        lock (locker)
        {
            return this.database.Table<Recipe>();
        }
    }

    public IEnumerable<Recipe> GetRecipeBySearchTerm(string text)
    {
        var recipes = GetRecipe();
        lock (locker)
        {
            return recipes.Where(m => m.RecipeName.ToLower().Contains(text));
        }
    }

添加using System.Linq 引用

改变这两个方法并返回IEnumerable

注意。 RecipeName 是您要过滤配方的属性。

你的搜索命令如下

private ICommand _searchCommand;
public ICommand SearchCommand
{
    get
    {
        return _searchCommand ?? (_searchCommand = new Command<string>((text) =>
        {
            var filteredRecipes = App.RecipeDbcontroller.GetRecipeBySearchTerm(text);

            recipes.Clear();
            foreach(var recipe in filteredRecipes )
                 recipes.Add(recipe);
        }));
    }
}

我没有测试过这段代码，所以不确定我可能会在哪里出错，但是你可以解决剩下的问题，因为逻辑已经给你了

祝你好运