[英]Binding an Observable Collection to a GridView
我的UWP需要有一個“收藏夾”頁面,允許用戶重新排序並保存頁面上的數據。 最初我的數據來自一個大型JSON文件,它使用Newtonsoft的Json.net進行反序列化,並在此字典中存儲在一個字典中,然后填充公共ObservableCollection。
這就是我現在迷失的地方,將ObservableCollection設置為DataContext,然后在XAML代碼中使用數據作為Binding,使用每個Item所需的所有標題,字幕和圖像填充GridView。 理論上這應該可以工作,但是在我的試驗和測試中,頁面仍然是空白的,而幕后的所有C#代碼似乎都應該填充它。
我不知道為什么頁面不適合我轉向你們所有人的集體幫助。
PS:我真的不關心這段代碼的整潔,我只是想讓它運轉起來。
XAML文件
<Page
x:Name="pageRoot"
x:Class="Melbourne_Getaway.FavouritesPage"
xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
xmlns:local="using:Melbourne_Getaway"
xmlns:data="using:Melbourne_Getaway.Data"
xmlns:common="using:Melbourne_Getaway.Common"
xmlns:d="http://schemas.microsoft.com/expression/blend/2008"
xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006"
mc:Ignorable="d">
<Page.Resources>
<x:String x:Key="AppName">Favourites</x:String>
</Page.Resources>
<!--
This grid acts as a root panel for the page that defines two rows:
* Row 0 contains the back button and page title
* Row 1 contains the rest of the page layout
-->
<Grid Background="{ThemeResource ApplicationPageBackgroundThemeBrush}">
<Grid.ChildrenTransitions>
<TransitionCollection>
<EntranceThemeTransition />
</TransitionCollection>
</Grid.ChildrenTransitions>
<Grid.RowDefinitions>
<RowDefinition Height="140" />
<RowDefinition Height="*" />
</Grid.RowDefinitions>
<GridView
x:Name="itemGridView"
AutomationProperties.AutomationId="ItemsGridView"
AutomationProperties.Name="Items"
TabIndex="1"
Grid.RowSpan="2"
Padding="60,136,116,46"
SelectionMode="None"
IsSwipeEnabled="false"
CanReorderItems="True"
CanDragItems="True"
AllowDrop="True"
ItemsSource="{Binding Items}">
<GridView.ItemTemplate>
<DataTemplate>
<Grid HorizontalAlignment="Left" Width="250" Height="107">
<Border Background="{ThemeResource ListViewItemPlaceholderBackgroundThemeBrush}">
<Image Source="{Binding ImagePath}" Stretch="UniformToFill" AutomationProperties.Name="{Binding Title}" />
</Border>
<StackPanel VerticalAlignment="Bottom" Background="{ThemeResource ListViewItemOverlayBackgroundThemeBrush}">
<TextBlock Text="{Binding Title}" Foreground="{ThemeResource ListViewItemOverlayForegroundThemeBrush}" Style="{StaticResource BaseTextBlockStyle}" Height="30" Margin="15,0,15,0" FontWeight="SemiBold" />
<TextBlock Text="{Binding Group}" Foreground="{ThemeResource ListViewItemOverlaySecondaryForegroundThemeBrush}" Style="{StaticResource BaseTextBlockStyle}" TextWrapping="NoWrap" Margin="15,-15,15,10" FontSize="12" />
</StackPanel>
</Grid>
</DataTemplate>
</GridView.ItemTemplate>
</GridView>
<!-- Back button and page title -->
<Grid>
<Grid.ColumnDefinitions>
<ColumnDefinition Width="120" />
<ColumnDefinition Width="*" />
</Grid.ColumnDefinitions>
<Button x:Name="backButton" Margin="39,59,39,0" Command="{Binding NavigationHelper.GoBackCommand, ElementName=pageRoot}"
Style="{StaticResource NavigationBackButtonNormalStyle}"
VerticalAlignment="Top"
AutomationProperties.Name="Back"
AutomationProperties.AutomationId="BackButton"
AutomationProperties.ItemType="Navigation Button" />
<TextBlock x:Name="pageTitle" Text="{StaticResource AppName}" Style="{StaticResource HeaderTextBlockStyle}" Grid.Column="1"
IsHitTestVisible="false" TextWrapping="NoWrap" VerticalAlignment="Bottom" Margin="0,0,30,40" />
</Grid>
</Grid>
CS檔案
using Melbourne_Getaway.Common;
using Melbourne_Getaway.Data;
using Newtonsoft.Json;
using System;
using System.Collections.Generic;
using System.Collections.ObjectModel;
using Windows.Storage;
using Windows.UI.Popups;
using Windows.UI.Xaml.Controls;
using Windows.UI.Xaml.Navigation;
namespace Melbourne_Getaway
{
public sealed partial class FavouritesPage : Page
{
public ObservableCollection<ItemData> Items { get; set; }
private ObservableDictionary defaultViewModel = new ObservableDictionary();
private NavigationHelper navigationHelper;
private RootObject jsonLines;
private StorageFile fileFavourites;
private Dictionary<string, ItemData> ItemData = new Dictionary<string, ItemData>();
public FavouritesPage()
{
loadJson();
getFavFile();
this.InitializeComponent();
this.navigationHelper = new NavigationHelper(this);
this.navigationHelper.LoadState += navigationHelper_LoadState;
}
private void setupObservableCollection()
{
Items = new ObservableCollection<ItemData>(ItemData.Values);
DataContext = Items;
}
private async void loadJson()
{
var file = await StorageFile.GetFileFromApplicationUriAsync(new Uri("ms-appx:///DataModel/SampleData.json"));
string lines = await FileIO.ReadTextAsync(file);
jsonLines = JsonConvert.DeserializeObject<RootObject>(lines);
feedItems();
}
private async void getFavFile()
{
Windows.Storage.StorageFolder storageFolder = Windows.Storage.ApplicationData.Current.LocalFolder;
fileFavourites = await storageFolder.GetFileAsync("MelbGetaway.fav");
}
private async void feedItems()
{
if (await FileIO.ReadTextAsync(fileFavourites) != "")
{
foreach (var line in await FileIO.ReadLinesAsync(fileFavourites))
{
foreach (var Group in jsonLines.Groups)
{
foreach (var Item in Group.Items)
{
if (Item.UniqueId == line)
{
var storage = new ItemData()
{
Title = Item.Title,
UniqueID = Item.UniqueId,
ImagePath = Item.ImagePath,
Group = Group.Title
};
ItemData.Add(storage.UniqueID, storage);
}
}
}
}
}
else
{//should only execute if favourites file is empty, first time use?
foreach (var Group in jsonLines.Groups)
{
foreach (var Item in Group.Items)
{
var storage = new ItemData()
{
Title = Item.Title,
UniqueID = Item.UniqueId,
ImagePath = Item.ImagePath,
Group = Group.Title
};
ItemData.Add(storage.UniqueID, storage);
await FileIO.AppendTextAsync(fileFavourites, Item.UniqueId + "\r\n");
}
}
}
setupObservableCollection();
}
public ObservableDictionary DefaultViewModel
{
get { return this.defaultViewModel; }
}
#region NavigationHelper loader
public NavigationHelper NavigationHelper
{
get { return this.navigationHelper; }
}
private async void MessageBox(string Message)
{
MessageDialog dialog = new MessageDialog(Message);
await dialog.ShowAsync();
}
private async void navigationHelper_LoadState(object sender, LoadStateEventArgs e)
{
var sampleDataGroups = await SampleDataSource.GetGroupsAsync();
this.defaultViewModel["Groups"] = sampleDataGroups;
}
#endregion NavigationHelper loader
#region NavigationHelper registration
protected override void OnNavigatedFrom(NavigationEventArgs e)
{
navigationHelper.OnNavigatedFrom(e);
}
protected override void OnNavigatedTo(NavigationEventArgs e)
{
navigationHelper.OnNavigatedTo(e);
}
#endregion NavigationHelper registration
}
public class ItemData
{
public string UniqueID { get; set; }
public string Title { get; set; }
public string Group { get; set; }
public string ImagePath { get; set; }
}
}
如果沒有一個好的Minimal,Complete和Verifiable代碼示例 ,就不可能確定是什么問題。 但是,您的代碼中會出現一個明顯的錯誤:
private void setupObservableCollection()
{
Items = new ObservableCollection<ItemData>(ItemData.Values);
DataContext = Items;
}
在您的XAML中,綁定到{Binding Items}
。 將DataContext
設置為Items
屬性值,正確的綁定實際上只是{Binding}
。
或者,如果你想保持XAML的方式,你必須設置DataContext = this;
代替。 當然,如果你這樣做,那么你會遇到一個問題,你似乎沒有提出INotifyPropertyChanged.PropertyChanged
,甚至實現該接口。 如果您確定在調用InitializeComponent()
方法之前設置了屬性,那么您可以使用它,但在您顯示的代碼中似乎並非如此。
因此,如果要將綁定設置為{Binding Items}
,還需要實現INotifyPropertyChanged
,並確保在實際設置屬性時使用屬性名稱"Items"
引發PropertyChanged
事件。
如果上述問題無法解決您的問題,請通過提供可靠地再現問題的良好MCVE來改進問題。
我想到了。 我的問題在於我試圖將數據傳遞給頁面本身的方式。 而不是使用DataContext = Items;
並嘗試以這種方式訪問數據。 我改為為GridView
設置直接的ItemsSource
。
最終結果只是將DataContext = Items
更改為itemGridView.ItemsSource = Items;
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