我正在尝试从服务器下载以字节为单位的图像，但图像不会显示。我得到一个正确的字节数组并调整大小。它可以从相机添加图片，但从互联网上添加图片时不起作用。
我已经确认图像已正确保存并正确下载，因为我可以复制字节数组并使用字节数组字符串显示它。
我在调试时发现了比较这两种方法的问题，而在execturepickcommand中它触发了我的"ItemSourceChanged"方法，但它没有使用AddImages方法触发。
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public class ImageGalleryPageModel
{
public ObservableCollection<ImageModel> Images
{
get { return images; }
}
private ObservableCollection<ImageModel> images = new ObservableCollection<ImageModel>();
}
这可以添加此类
中的图片private async Task ExecutePickCommand()
{
MediaFile file = await CrossMedia.Current.PickPhotoAsync();
if (file == null)
return;
byte[] imageAsBytes;
using (MemoryStream memoryStream = new MemoryStream())
{
file.GetStream().CopyTo(memoryStream);
file.Dispose();
imageAsBytes = memoryStream.ToArray();
}
if (imageAsBytes.Length > 0)
{
IImageResizer resizer = DependencyService.Get<IImageResizer>();
imageAsBytes = resizer.ResizeImage(imageAsBytes, 1080, 1080);
ImageSource imageSource = ImageSource.FromStream(() => new MemoryStream(imageAsBytes));
Images.Add(new ImageModel { Source = imageSource, OrgImage = imageAsBytes });
}
}
然后我下载图像并将它们放入Collection，
private void AddTheImages(int imageIssueId)
{
var imageData = App.Client.GetImage(imageIssueId);
byte[] imageAsBytes = imageData.Item1;
if (imageAsBytes.Length > 0)
{
IImageResizer resizer = DependencyService.Get<IImageResizer>();
imageAsBytes = resizer.ResizeImage(imageAsBytes, 1080, 1080);
ImageSource imageSource = ImageSource.FromStream(() => new MemoryStream(imageAsBytes));
ImageGalleryViewModel.Images.Add(new ImageModel { Source = imageSource, OrgImage = imageAsBytes });
}
}
的Xaml
<freshMvvm:FreshBaseContentPage NavigationPage.HasNavigationBar="False"
xmlns="http://xamarin.com/schemas/2014/forms"
xmlns:x="http://schemas.microsoft.com/winfx/2009/xaml"
xmlns:freshMvvm="clr-namespace:FreshMvvm;assembly=FreshMvvm"
xmlns:converters="clr-namespace:ASFT.Converters;assembly=ASFT"
xmlns:controls="clr-namespace:ASFT.Controls;assembly=ASFT"
x:Class="ASFT.Pages.IssuePage"
Padding="4,25,4,4"
x:Name="IssuePages">
...
<!--PictureGallery-->
<Label Text="IMAGES"
HorizontalTextAlignment="Start"
VerticalTextAlignment="Center"
Style="{StaticResource Labelfont}"
TextColor="White" />
<Grid BindingContext="{Binding ImageGalleryViewModel}">
<Grid.RowDefinitions>
<RowDefinition Height="128" />
<RowDefinition Height="*" />
</Grid.RowDefinitions>
<controls:ImageGalleryControl Grid.Row="0"
ItemsSource="{Binding Images}">
<controls:ImageGalleryControl.ItemTemplate>
<DataTemplate>
<Image Source="{Binding Source}"
Aspect="AspectFit">
<Image.GestureRecognizers>
<TapGestureRecognizer
Command="{Binding Path=BindingContext.PreviewImageCommand, Source={x:Reference IssuePages}}"
CommandParameter="{Binding ImageId}" />
</Image.GestureRecognizers>
</Image>
</DataTemplate>
</controls:ImageGalleryControl.ItemTemplate>
</controls:ImageGalleryControl>
<Grid Grid.Row="1">
<Grid.ColumnDefinitions>
<ColumnDefinition Width="*" />
<ColumnDefinition Width="*" />
</Grid.ColumnDefinitions>
<Button Grid.Column="0"
Text="Add photo"
Command="{Binding CameraCommand}" />
<Button Grid.Column="1"
Text="Pick photo"
Command="{Binding PickCommand}" />
</Grid>
</Grid>
<Label Grid.Column="0"
Grid.Row="3"
Grid.ColumnSpan="3"
Text="{Binding ImageText}"
HorizontalTextAlignment="Center"
VerticalTextAlignment="Center"
TextColor="White" />
...
</freshMvvm:FreshBaseContentPage>
这就是Control，它是itemsourcechanged，它不是触发器。
private readonly StackLayout imageStack;
public ImageGalleryControl()
{
this.Orientation = ScrollOrientation.Horizontal;
imageStack = new StackLayout
{
Orientation = StackOrientation.Horizontal
};
this.Content = imageStack;
}
public new IList<View> Children
{
get { return imageStack.Children; }
}
public static readonly BindableProperty ItemsSourceProperty =
BindableProperty.Create<ImageGalleryControl, IList>
(
view => view.ItemsSource,
default(IList),
BindingMode.TwoWay,
propertyChanging: (bindableObject, oldValue, newValue) =>
{
((ImageGalleryControl)bindableObject).ItemsSourceChanging();
},
propertyChanged: (bindableObject, oldValue, newValue) =>
{
((ImageGalleryControl)bindableObject).ItemsSourceChanged(bindableObject, oldValue, newValue);
}
);
public IList ItemsSource
{
get { return (IList)GetValue(ItemsSourceProperty); }
set { SetValue(ItemsSourceProperty, value); }
}
private void ItemsSourceChanging()
{
if (ItemsSource == null)
return;
}
private void CreateNewItem(IList newItem)
{
View view = (View)ItemTemplate.CreateContent();
if (view is BindableObject bindableObject)
bindableObject.BindingContext = newItem;
imageStack.Children.Add(view);
}
private void ItemsSourceChanged(BindableObject bindable, IList oldValue, IList newValue)
{
if (ItemsSource == null)
return;
if (newValue is INotifyCollectionChanged notifyCollection)
{
notifyCollection.CollectionChanged += (sender, args) =>
{
if (args.NewItems != null)
{
if (args.NewItems.Count > 0)
{
foreach (object newItem in args.NewItems)
{
View view = (View)ItemTemplate.CreateContent();
if (view is BindableObject bindableObject)
bindableObject.BindingContext = newItem;
imageStack.Children.Add(view);
}
}
}
else
{
imageStack.Children.Clear();
foreach (object item in ItemsSource)
{
View view = (View)ItemTemplate.CreateContent();
BindableObject bindableObject = (BindableObject) view;
if (bindableObject != null)
bindableObject.BindingContext = item;
imageStack.Children.Add(view);
}
}
if (args.OldItems != null)
{
// not supported
}
};
}
}
public DataTemplate ItemTemplate
{
get;
set;
}
public static readonly BindableProperty SelectedItemProperty =
BindableProperty.Create<ImageGalleryControl, object>
(
view => view.SelectedItem,
null,
BindingMode.TwoWay,
propertyChanged: (bindable, oldValue, newValue) =>
{
((ImageGalleryControl)bindable).UpdateSelectedIndex();
}
);
public object SelectedItem
{
get { return GetValue(SelectedItemProperty); }
set { SetValue(SelectedItemProperty, value); }
}
private void UpdateSelectedIndex()
{
if (SelectedItem == BindingContext)
return;
SelectedIndex = Children
.Select(c => c.BindingContext)
.ToList()
.IndexOf(SelectedItem);
}
public static readonly BindableProperty SelectedIndexProperty =
BindableProperty.Create<ImageGalleryControl, int>
(
carousel => carousel.SelectedIndex,
0,
BindingMode.TwoWay,
propertyChanged: (bindable, oldValue, newValue) =>
{
((ImageGalleryControl)bindable).UpdateSelectedItem();
}
);
public int SelectedIndex
{
get { return (int)GetValue(SelectedIndexProperty); }
set { SetValue(SelectedIndexProperty, value); }
}
private void UpdateSelectedItem()
{
SelectedItem = SelectedIndex > -1 ? Children[SelectedIndex].BindingContext : null;
}
}
答案 0 :(得分：1)
public ObservableCollection<> Images {get;set;} = new ObservableCollection<>(); 具有通用ImageModel。 您不需要私有字段，这没有任何意义。