如何加载图像缩略图以从IsolatedStorage查看

Question

I currently have several hundred images in IsolatedStorage of my application (which may turn to thousands), and the loading time is rediculously slow. Often times my application freezes and fails. The user is allowed to use the CameraCaptureTask to take pictures, and then each picture is saved to IsolatedStorage as well as shown in the View using a LongListSelector. I've tried using a ViewBox and setting the GridCellSize of the LongListSelector to a small size (max width or height depending on aspect ratio of 108), but this does not help in reducing the time or actual image size when loading from IsolatedStorage. I was wondering if there was a quick way to speed up the loading/rendering time by loading a thumbnail sized version of an image from IsolatedStorage to populate the view? Then once an image in the view is selected, I will pull only that image from IsolatedStorage.

MainPage.xaml

<phone:PhoneApplicationPage.Resources>

<Style x:Key="PhoneButtonBase" TargetType="ButtonBase">
    <Setter Property="Background" Value="Transparent"/>
    <Setter Property="BorderBrush" Value="{StaticResource PhoneForegroundBrush}"/>
    <Setter Property="Foreground" Value="{StaticResource PhoneForegroundBrush}"/>
    <Setter Property="BorderThickness" Value="{StaticResource PhoneBorderThickness}"/>
    <Setter Property="FontFamily" Value="{StaticResource PhoneFontFamilySemiBold}"/>
    <Setter Property="FontSize" Value="{StaticResource PhoneFontSizeMedium}"/>
    <Setter Property="Padding" Value="10,5,10,6"/>
    <Setter Property="Template">
        <Setter.Value>
            <ControlTemplate TargetType="ButtonBase">
                <Grid Background="Transparent">
                    <VisualStateManager.VisualStateGroups>
                        <VisualStateGroup x:Name="CommonStates">
                            <VisualState x:Name="Normal"/>
                            <VisualState x:Name="MouseOver"/>
                            <VisualState x:Name="Pressed">
                                <Storyboard>
                                    <ObjectAnimationUsingKeyFrames Storyboard.TargetProperty="Foreground" Storyboard.TargetName="ContentContainer">
                                        <DiscreteObjectKeyFrame KeyTime="0" Value="{StaticResource PhoneButtonBasePressedForegroundBrush}"/>
                                    </ObjectAnimationUsingKeyFrames>
                                    <ObjectAnimationUsingKeyFrames Storyboard.TargetProperty="Background" Storyboard.TargetName="ButtonBackground">
                                        <DiscreteObjectKeyFrame KeyTime="0" Value="{StaticResource PhoneAccentBrush}"/>
                                    </ObjectAnimationUsingKeyFrames>
                                </Storyboard>
                            </VisualState>
                            <VisualState x:Name="Disabled">
                                <Storyboard>
                                    <ObjectAnimationUsingKeyFrames Storyboard.TargetProperty="Foreground" Storyboard.TargetName="ContentContainer">
                                        <DiscreteObjectKeyFrame KeyTime="0" Value="{StaticResource PhoneDisabledBrush}"/>
                                    </ObjectAnimationUsingKeyFrames>
                                    <ObjectAnimationUsingKeyFrames Storyboard.TargetProperty="BorderBrush" Storyboard.TargetName="ButtonBackground">
                                        <DiscreteObjectKeyFrame KeyTime="0" Value="{StaticResource PhoneDisabledBrush}"/>
                                    </ObjectAnimationUsingKeyFrames>
                                    <ObjectAnimationUsingKeyFrames Storyboard.TargetProperty="Background" Storyboard.TargetName="ButtonBackground">
                                        <DiscreteObjectKeyFrame KeyTime="0" Value="Transparent"/>
                                    </ObjectAnimationUsingKeyFrames>
                                </Storyboard>
                            </VisualState>
                        </VisualStateGroup>
                    </VisualStateManager.VisualStateGroups>
                    <Border x:Name="ButtonBackground" BorderBrush="{TemplateBinding BorderBrush}" BorderThickness="{TemplateBinding BorderThickness}" Background="{TemplateBinding Background}" CornerRadius="0" Margin="{StaticResource PhoneTouchTargetOverhang}">
                        <ContentControl x:Name="ContentContainer" ContentTemplate="{TemplateBinding ContentTemplate}" Content="{TemplateBinding Content}" Foreground="{TemplateBinding Foreground}" HorizontalContentAlignment="{TemplateBinding HorizontalContentAlignment}" Padding="{TemplateBinding Padding}" VerticalContentAlignment="{TemplateBinding VerticalContentAlignment}"/>
                    </Border>
                </Grid>
            </ControlTemplate>
        </Setter.Value>
    </Setter>
</Style>
<Style x:Key="PhoneRadioButtonCheckBoxBase" BasedOn="{StaticResource PhoneButtonBase}" TargetType="ToggleButton">
    <Setter Property="Background" Value="{StaticResource PhoneRadioCheckBoxBrush}"/>
    <Setter Property="BorderBrush" Value="{StaticResource PhoneRadioCheckBoxBorderBrush}"/>
    <Setter Property="FontSize" Value="{StaticResource PhoneFontSizeMedium}"/>
    <Setter Property="FontFamily" Value="{StaticResource PhoneFontFamilyNormal}"/>
    <Setter Property="HorizontalContentAlignment" Value="Left"/>
    <Setter Property="VerticalContentAlignment" Value="Center"/>
    <Setter Property="Padding" Value="0"/>
</Style>
<Style x:Key="RadioButtonStyle1" BasedOn="{StaticResource PhoneRadioButtonCheckBoxBase}" TargetType="RadioButton">
    <Setter Property="Template">
        <Setter.Value>
            <ControlTemplate TargetType="RadioButton">
                <Grid Background="Transparent">
                    <VisualStateManager.VisualStateGroups>
                        <VisualStateGroup x:Name="CommonStates">
                            <VisualState x:Name="Normal"/>
                            <VisualState x:Name="MouseOver"/>
                            <VisualState x:Name="Pressed"/>
                            <VisualState x:Name="Disabled">
                                <Storyboard>
                                    <ObjectAnimationUsingKeyFrames Storyboard.TargetProperty="Foreground" Storyboard.TargetName="ContentContainer">
                                        <DiscreteObjectKeyFrame KeyTime="0" Value="{StaticResource PhoneDisabledBrush}"/>
                                    </ObjectAnimationUsingKeyFrames>
                                </Storyboard>
                            </VisualState>
                        </VisualStateGroup>
                        <VisualStateGroup x:Name="CheckStates">
                            <VisualState x:Name="Checked"/>
                            <VisualState x:Name="Unchecked"/>
                            <VisualState x:Name="Indeterminate"/>
                        </VisualStateGroup>
                    </VisualStateManager.VisualStateGroups>
                    <ContentControl x:Name="ContentContainer" ContentTemplate="{TemplateBinding ContentTemplate}" Content="{TemplateBinding Content}" Foreground="{TemplateBinding Foreground}" FontSize="{TemplateBinding FontSize}" FontFamily="{TemplateBinding FontFamily}" HorizontalContentAlignment="{TemplateBinding HorizontalContentAlignment}" Padding="{TemplateBinding Padding}" VerticalContentAlignment="{TemplateBinding VerticalContentAlignment}"/>
                </Grid>
            </ControlTemplate>
        </Setter.Value>
    </Setter>
</Style>

..

            <phone:LongListSelector.ItemTemplate>
                <DataTemplate>
                    <ContentControl HorizontalAlignment="Stretch" HorizontalContentAlignment="Left">
                        <ContentControl.Resources>
                            <Storyboard x:Name="CheckedStoryboard">
                                <ColorAnimation Duration="0" To="#FF1BA1E2" Storyboard.TargetProperty="(Border.BorderBrush).(SolidColorBrush.Color)" Storyboard.TargetName="brd" d:IsOptimized="True"/>
                            </Storyboard>
                        </ContentControl.Resources>
                        <RadioButton x:Name="radioButton" HorizontalAlignment="Stretch" Margin="0,0,0,0" GroupName="A" Background="Black" Style="{StaticResource RadioButtonStyle1}" >
                            <i:Interaction.Triggers>
                                <i:EventTrigger EventName="Click">
                                    <eim:ControlStoryboardAction Storyboard="{StaticResource CheckedStoryboard}"/>
                                </i:EventTrigger>
                                <i:EventTrigger EventName="Unchecked">
                                    <eim:ControlStoryboardAction ControlStoryboardOption="Stop" Storyboard="{StaticResource CheckedStoryboard}"/>
                                </i:EventTrigger>
                            </i:Interaction.Triggers>
                            <Border x:Name="MyBorder" Background="Transparent">
                                <Border x:Name="brd" CornerRadius="10" Width="Auto" BorderThickness="3" BorderBrush="Transparent">
                                    <toolkit:ContextMenuService.ContextMenu>
                                        <toolkit:ContextMenu x:Name="imgListContextMenu" Background="{StaticResource PhoneChromeBrush}">                                                                                                        <toolkit:MenuItem Foreground="{StaticResource PhoneForegroundBrush}" Header="{Binding Path=LocalizedResources.MainPage_ContextMenu_Delete, Source={StaticResource LocalizedStrings}}" Click="deleteContextMenuItem_Click"/>
                                        </toolkit:ContextMenu>
                                    </toolkit:ContextMenuService.ContextMenu>
                                    <Viewbox Width="108" Height="108">
                                        <Image x:Name="recentImage" Source="{Binding Source}" Margin="6,6" Width="108"/>
                                    </Viewbox>
                                </Border>
                            </Border>
                        </RadioButton>
                    </ContentControl>
                </DataTemplate>
            </phone:LongListSelector.ItemTemplate>

        </phone:LongListSelector>

MainPage.xaml.cs

protected override void OnNavigatedTo(NavigationEventArgs e)
{   
    if (Settings.AscendingSort.Value)
    {
        App.PictureList.Pictures = new ObservableCollection<Models.Picture>(App.PictureList.Pictures.OrderBy(x => x.DateTaken)); 
        Recent.ItemsSource = App.PictureList.Pictures;
    }
    else
    {
        App.PictureList.Pictures = new ObservableCollection<Models.Picture>(App.PictureList.Pictures.OrderByDescending(x => x.DateTaken));
        Recent.ItemsSource = App.PictureList.Pictures;
    }    
}

...

private void cameraTask_Completed(object sender, PhotoResult e)
{
    if (e.TaskResult == TaskResult.OK)
    {
        var capturedPicture = new CapturedPicture(e.OriginalFileName, stream);
    }
}

private void recent_SelectionChanged(object sender, SelectionChangedEventArgs e)
{
    var item = (sender as LongListSelector).SelectedItem;
    if (item == null)
        return;

    capturedPicture = null; 
    //Get picture
    capturedPicture = (sender as LongListSelector).SelectedItem as CapturedPicture;

    if (capturedPicture != null)
    {                
        fileName = capturedPicture.FileName;
    }
}

App.xaml.cs

public static PictureRepository PictureList
{
    get
    {
        return PictureRepository.Instance;
    }
}

PictureRepository.cs

#region Constants

public const string IsolatedStoragePath = "Pictures";

#endregion

#region Fields

private ObservableCollection<Picture> _pictures = new ObservableCollection<Picture>();

#endregion

#region Properties

public ObservableCollection<Picture> Pictures
{
    get { return _pictures; }
    set{ pictures = value; }
}

#endregion

#region Singleton Pattern

private PictureRepository()
{
    LoadAllPicturesFromIsolatedStorage();
}

public static readonly PictureRepository Instance = new PictureRepository();

#endregion

/// <summary>        
/// Saves to local storage
/// This method gets two parameters: the captured picture instance and the name of the pictures folder in the isolated storage
/// </summary>
/// <param name="capturedPicture"></param>
/// <param name="directory"></param>
public void SaveToLocalStorage(CapturedPicture capturedPicture, string directory)
{
    //call IsolatedStorageFile.GetUserStoreForApplication to get an isolated storage file
    var isoFile = IsolatedStorageFile.GetUserStoreForApplication();
    //Call the IsolatedStorageFile.EnsureDirectory extension method located in the Common IsolatedStorageFileExtensions class to confirm that the pictures folder exists.
    isoFile.EnsureDirectory(directory);

    //Combine the pictures folder and captured picture file name and use this path to create a new file 
    string filePath = Path.Combine(directory, capturedPicture.FileName);
    using (var fileStream = isoFile.CreateFile(filePath))
    {
        using (var writer = new BinaryWriter(fileStream))
        {
            capturedPicture.Serialize(writer);
        }
    }
}

/// <summary>
/// To load all saved pictures and add them to the pictures list page
/// </summary>
public CapturedPicture LoadFromLocalStorage(string fileName, string directory)
{
    //To open the file, add a call to the IsolatedStorageFile.GetUserStoreForApplication
    var isoFile = IsolatedStorageFile.GetUserStoreForApplication();

    //Combine the directory and file name
    string filePath = Path.Combine(directory, fileName);
    //use the path to open the picture file from the isolated storage by using the IsolatedStorageFile.OpenFile method
    using (var fileStream = isoFile.OpenFile(filePath, FileMode.Open, FileAccess.Read))
    {
        //create a BinaryReader instance for deserializing the CapturedPicture instance
        using (var reader = new BinaryReader(fileStream))
        {
            var capturedPicture = new CapturedPicture();
            //create a new instance of the type CapturedPicture called CapturedPicture.Deserialize to deserialize the captured picture and return it
            capturedPicture.Deserialize(reader);
            return capturedPicture;
        }
    }
}

/// <summary>
/// To load all the pictures at start time
/// </summary>
private void LoadAllPicturesFromIsolatedStorage()
{
    //add call to the IsolatedStorageFile.GetUserStoreForApplication to open an isolated storage file
    var isoFile = IsolatedStorageFile.GetUserStoreForApplication();
    //Call the IsolatedStorageFile.EnsureDirectory extension method located in the Common IsolatedStorageFileExtensions class to confirm that the pictures folder exists
    isoFile.EnsureDirectory(IsolatedStoragePath);

    //Call the IsolatedStorageFile.GetFileNames using the pictures directory and *.jpg as a filter to get all saved pictures
    var pictureFiles = isoFile.GetFileNames(Path.Combine(IsolatedStoragePath, "*.jpg"));
    //var pictureFiles = isoFile.GetFileNames(Path.Combine(IsolatedStoragePath, ""));

    //Iterate through all the picture files in the list and load each using the LoadFromLocalStorage you created earlier
    foreach (var pictureFile in pictureFiles)
    {
        var picture = LoadFromLocalStorage(pictureFile, IsolatedStoragePath);
        _pictures.Add(picture);
    }
}

LoadAllPicturesFromIsolatedStorage is where the images from IsolatedStorage are being loaded, what would be the best and most efficient way to reduce the image size to a max width or height of 108 to decrease loading/rendering time? And is this the best way to go about this in the first place? Any help, suggestions, or thoughts would be greatly appreciated.

EDIT: added CapturedPicture.cs, Picture.cs

CapturedPicture.cs

[DataContract]
public class CapturedPicture : Picture
{
    [DataMember]
    public byte[] ImageBytes
    {
        get;
        set;
    }

    [DataMember]
    public string FileName
    {
        get;
        set;
    }

    protected override BitmapSource CreateBitmapSource()
    {
        BitmapSource source = null;
        if (ImageBytes != null)
        {
            using (var stream = new MemoryStream(ImageBytes))
            {
                source = PictureDecoder.DecodeJpeg(stream);
                //source = PictureDecoder.DecodeJpeg(stream, 500, 500);
            }
        }
        return source;
    }

    public CapturedPicture()
    {
    }

    public CapturedPicture(string capturedFileName, Stream capturedImageStream)
    {
        ImageBytes = ReadImageBytes(capturedImageStream);
        //DateTaken = DateTime.Now.ToLongDateString();
        //DateTaken = DateTime.Now.ToString();
        //DateTaken = DateTime.Now.ToString("o");
        DateTaken = DateTime.UtcNow;
        FileName = System.IO.Path.GetFileName(capturedFileName);
    }

    private byte[] ReadImageBytes(Stream imageStream)
    {
        byte[] imageBytes = new byte[imageStream.Length];
        imageStream.Read(imageBytes, 0, imageBytes.Length);
        return imageBytes;
    }

    public override void Serialize(BinaryWriter writer)
    {
        base.Serialize(writer);
        writer.Write(ImageBytes.Length);
        writer.Write(ImageBytes);
        writer.Write(FileName);//writer.WriteString(FileName);
    }

    public override void Deserialize(BinaryReader reader)
    {
        base.Deserialize(reader);
        int bytesCount = reader.ReadInt32();
        ImageBytes = reader.ReadBytes(bytesCount);
        FileName = reader.ReadString();
    }

Picture.cs

[DataMember]
public string Address
{
    get { return GetValue(() => Address); }
    set { SetValue(() => Address, value); }
}

[DataMember]
public string Note
{
    get { return GetValue(() => Note); }
    set { SetValue(() => Note, value); }
}

[DataMember]
public DateTime DateTaken
{
    get { return GetValue(() => DateTaken); }
    set { SetValue(() => DateTaken, value); }
}

[IgnoreDataMember]
public BitmapSource Source
{
    get
    {
        return CreateBitmapSource();
    }
}

protected abstract BitmapSource CreateBitmapSource();

//In the Serialize method, store the Position, Address, Note, and DateTaken properties
public virtual void Serialize(BinaryWriter writer)
{            
    writer.Write(DateTaken.ToString()); //writer.WriteString(DateTaken);
}

//In the Deserialize method, read the data in the same order you’ve written it
public virtual void Deserialize(BinaryReader reader)
{
    DateTaken = DateTime.Parse(reader.ReadString());
}

Answer 1

If I had to guess from looking at the code, your problem is that you are not allowing the phone framework to load the images on demand when their container is scrolled into view. Your code is going to decode every one of those files immediately on page load rather than as they become visible. You're also using the deprecated isolated storage API instead of the new asynchronous Windows.Storage namespace, which is likely going to block your UI thread.

You can refactor this however you'd prefer, but consider something similar to the following:

Code Behind

public partial class MyPage : PhoneApplicationPage
{
    public MyPage()
    {
        InitializeComponent();

        this.Loaded += async (sender, e) =>
        {
            var folder = await ApplicationData.Current.LocalFolder.GetFolderAsync("Pictures");
            var images = await folder.GetFilesAsync();
            Recent.ItemsSource = images.ToList();
        };
    }
}

XAML

<phone:LongListSelector x:Name="Recent" Margin="0,0,0,72" LayoutMode="Grid" GridCellSize="108,108">
    <phone:LongListSelector.ItemTemplate>
        <DataTemplate>
            <Image Source="{Binding Path}" Margin="6" Stretch="UniformToFill" VerticalAlignment="Center" HorizontalAlignment="Center"/>
        </DataTemplate>
    </phone:LongListSelector.ItemTemplate>
</phone:LongListSelector>

This is an overly simplistic example, but the upshot is that you can build a list of StorageFile and bind your LongListSelector.ItemSource property to it. The Image.Source dependency property is pretty malleable, so you can pass it the image file's path string directly and it will do the heavy lifting of creating an image source object for you, scaled and cropped to the specifications of the image container. This process only occurs as the image is scrolled into view so you'll only ever have a handful of images loaded at a time. The LongListSelector will do the work of rendering the item templates on demand for you as the user scrolls the list, generating the new Image controls and its Source at that time.

If for whatever reason you feel the need to transform these records to your CapturedPicture class, feel free. The one most important piece of information you'll need to map is the Path property from these file objects, as it is a valid URI to provide to the image control as the Source binding.

--EDIT--

I've added code that demonstrates, if nothing else, the changed loading process. I've wired up the INotifyPropertyChanged interface for this repo so that the UI will be notified of changes to the Pictures collection and changed the setter to private (this is an assumption on my part about your desired behavior).

For read and write operations, you can check out extensions for the StorageFile class in the System.IO namespace. Just import it in a using directive and you'll have access to the following:

• OpenStreamForReadAsync
• OpenStreamForWriteAsync

Implementation of the save method may be much more complex depending on what you accept as a parameter for the save directory. If you allow for specifying a directory parameter with a full path of multiple subdirectories, that would change the code substantially from just allowing saving to a first-level subdirectory. You'd have to check for the existence of each subfolder and create it if not. Otherwise, the code sample below for accessing the Pictures folder should suffice to demonstrate how to obtain the target folder.

Sample PictureRepository.cs

using System;
using System.Collections.ObjectModel;
using System.ComponentModel;
using System.Threading.Tasks;
using Windows.Storage;
using Windows.Storage.Search;

namespace MyApp.Media
{
    public class PictureRepository : INotifyPropertyChanged
    {
        #region Constants

        public const string IsolatedStoragePath = "Pictures";

        #endregion

        #region Fields

        private ObservableCollection<StorageFile> _pictures = new ObservableCollection<StorageFile>();

        #endregion

        #region Properties

        public ObservableCollection<StorageFile> Pictures
        {
            get { return _pictures; }
            private set
            {
                RaisePropertyChanged("Pictures");
                _pictures = value;
            }
        }

        #endregion

        #region INotifyPropertyChanged

        public event PropertyChangedEventHandler PropertyChanged;

        private void RaisePropertyChanged(string propertyName)
        {
            if (PropertyChanged != null)
            {
                PropertyChanged(this, new PropertyChangedEventArgs(propertyName));
            }
        }

        #endregion

        #region Singleton Pattern

        private PictureRepository()
        {
            // This call will warn that execution of the method will continue without waiting on completion
            // This is unimportant because the remainder of the constructor is not dependent on its initialization
            // and the UI will be notified of the change in the collection and respond at that time
            LoadAllPicturesFromIsolatedStorageAsync();
        }

        public static readonly PictureRepository Instance = new PictureRepository();

        #endregion

        /// <summary>
        /// To load all the pictures at start time
        /// </summary>
        private async Task LoadAllPicturesFromIsolatedStorageAsync()
        {
            // Create or open the target folder
            var folder = await ApplicationData.Current.LocalFolder.CreateFolderAsync(IsolatedStoragePath, CreationCollisionOption.OpenIfExists);

            // Create a query for files with the JPEG extension
            var query = folder.CreateFileQueryWithOptions(new QueryOptions(CommonFileQuery.OrderByName, new string[] { ".jpg" }));

            // Update the Pictures collection, which will raise the PropertyChanged event and cause the UI to bind
            Pictures = new ObservableCollection<StorageFile>(await query.GetFilesAsync());
        }
    }
}