CollectionView預選不適用于xamarin表單

我想在集合視圖中有一個預先選擇的專案，但它不起作用。正在將資料從視圖模型發送到集合視圖。我想在集合視圖中預選一項。我需要 xamarin 方面的幫助。這是我的代碼

xml

<CollectionView x:Name="WorkerFlockView" ItemsSource="{Binding WorkerFlockDetails}" SelectedItem="{Binding SelectedFlock}" SelectionMode="Single" SelectionChangedCommand="{Binding ViewFlockControlPointsCommand}" HeightRequest="100">
                    <CollectionView.ItemsLayout>
                        <LinearItemsLayout Orientation="Horizontal" ItemSpacing="10" />
                    </CollectionView.ItemsLayout>
                    <CollectionView.ItemTemplate>
                        <DataTemplate>
                            <Grid>
                                <Frame Margin="0,0,0,0" Padding="0" HorizontalOptions="CenterAndExpand" BackgroundColor="#F7F7F7" Opacity="0.93" HasShadow="{OnPlatform Android=true, iOS=false}"  CornerRadius="0" IsClippedToBounds="True" >
                                    <StackLayout Orientation="Vertical" Opacity="1">
                                        <StackLayout HeightRequest="15" BackgroundColor="#105CA5"></StackLayout>
                                        <StackLayout Orientation="Vertical" Padding="10,0,10,0" VerticalOptions="CenterAndExpand">
                                            <StackLayout Orientation="Horizontal">
                                                <Label Text="Flock" TextColor="#105CA5"></Label>
                                                <Label Text="{Binding Flock_name}"></Label>
                                            </StackLayout>
                                            <StackLayout Orientation="Horizontal">
                                                <Label Text="Farm" TextColor="#105CA5"></Label>
                                                <Label Text="{Binding Farm_name}"></Label>
                                            </StackLayout>
                                            <StackLayout Orientation="Horizontal">
                                                <Label Text="House" TextColor="#105CA5"></Label>
                                                <Label Text="{Binding House_name}"></Label>
                                            </StackLayout>
                                            <StackLayout Orientation="Horizontal">
                                                <Label Text="Age" TextColor="#105CA5"></Label>
                                                <Label Text="{Binding Flock_age}"></Label>
                                            </StackLayout>
                                            <StackLayout Orientation="Horizontal">
                                                <Label Text="Bird Type" TextColor="#105CA5"></Label>
                                                <Label Text="{Binding Bird_type}"></Label>
                                            </StackLayout>
                                            <StackLayout Orientation="Horizontal">
                                                <Label Text="Number of birds" TextColor="#105CA5"></Label>
                                                <Label Text="{Binding Number_of_birds}"></Label>
                                            </StackLayout>

                                        </StackLayout>
                                    </StackLayout>
                                </Frame>

                                <VisualStateManager.VisualStateGroups >
                                    <VisualStateGroup Name="CommonStates">
                                        <VisualState Name="Normal" />
                                        <VisualState Name="Selected">
                                            <VisualState.Setters>
                                                <Setter Property="BackgroundColor" Value="Blue" />

                                            </VisualState.Setters>
                                        </VisualState>
                                    </VisualStateGroup>
                                </VisualStateManager.VisualStateGroups>
                            </Grid>
                        </DataTemplate>
                    </CollectionView.ItemTemplate>
                </CollectionView>

查看模型

類 HomeWorkerViewModel ：INotifyPropertyChanged {

public HomeWorkerViewModel(){

   WorkerFlockDetails = new ObservableCollection<WorkerFlock>();

   selectedFlock = WorkerFlockDetails.Skip(3).FirstOrDefault();

  //function for adding information
  Init();
}

//Populate WorkerFlockDetails with data
function Init()


public ObservableCollection<WorkerFlock> workerFlockDetails;
    public ObservableCollection<WorkerFlock> WorkerFlockDetails
    {
        get => workerFlockDetails;
        set
        {
            workerFlockDetails = value;
            PropertyChanged?.Invoke(this, new PropertyChangedEventArgs(nameof(WorkerFlockDetails)));
        }
    }

private WorkerFlock selectedFlock { get; set; }
    public WorkerFlock SelectedFlock
    {
        get { return selectedFlock; }
        set
        {
            if (selectedFlock != value)
            {
                try
                {
                    //Feed = selectedFlock.Feed_intake.ToString()   " Kg";
                    selectedFlock = value;                       

                }
                catch
                {

                }
            }
        }
    }


}

uj5u.com熱心網友回復：

有幾件事：

1. ObservableCollection類自動實作了一個 Notify 方法，因此您不需要私有欄位并呼叫PropertyChanged

   公共 ObservableCollection WorkerFlockDetails { 獲取；放; }

2. 修改時應該呼叫 PropertyChanged SelectedFlock

   private WorkerFlock selectedFlock;
   public WorkerFlock SelectedFlock
   {
        get => selectedFlock
        set
        {
            if (selectedFlock != value)
            {
                try
                {
                    //Feed = selectedFlock.Feed_intake.ToString()   " Kg";
                    selectedFlock = value;    
                }
                catch
                {
   
                }
                finally 
                {
                 PropertyChanged?.Invoke(this, new PropertyChangedEventArgs(nameof(SelectedFlock)));
                }
            }
        }
    }
   

3. 讓我們轉到建構式。如果該Init() 方法用資料填充您的 ObservableCollection，您應該在選擇 Item 之前呼叫它，否則集合將為空

并且在使用代碼更改選擇時，您應該呼叫公共屬性而不是私有屬性，因為它會通知 UI 它已更改

public HomeWorkerViewModel(){

   WorkerFlockDetails = new ObservableCollection<WorkerFlock>();
    
   //Call init before selection
   //function for adding information. 
   Init();

   //Use public property
   SelectedFlock = WorkerFlockDetails.Skip(3).FirstOrDefault();

}

快樂編碼！

標籤：C＃ xml 沙马林 xamarin.forms

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