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[DllImport("gdi32.dll", EntryPoint = "DeleteObject")]
[return: MarshalAs(UnmanagedType.Bool)]
public static extern bool DeleteObject([In] IntPtr hObject);

public static ImageSource ToImageSource(this Bitmap bmp)
{
    var handle = bmp.GetHbitmap();
    try
    {
        return Imaging.CreateBitmapSourceFromHBitmap(handle, IntPtr.Zero, Int32Rect.Empty, BitmapSizeOptions.FromEmptyOptions());

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public static BitmapSource Resize(this BitmapSource source, int resolution)
{
    var scale = resolution / source.DpiX;

    // サイズ変更
    var transformedBitmap = new TransformedBitmap();
    transformedBitmap.BeginInit();
    transformedBitmap.Source = source;
    transformedBitmap.Transform = new ScaleTransform(scale, scale);
    transformedBitmap.EndInit();

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public static BitmapSource Resize(this BitmapSource source, int resolution)
{
    var scale = resolution / source.DpiX;

    // サイズ変更
    var transformedBitmap = new TransformedBitmap();
    transformedBitmap.BeginInit();
    transformedBitmap.Source = source;
    transformedBitmap.Transform = new ScaleTransform(scale, scale);
    transformedBitmap.EndInit();

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public static BitmapSource Rotation(this BitmapSource source, int angle)
{
    if (source == null) throw new ArgumentNullException(nameof(source));

    var transformedBitmap = new TransformedBitmap();
    transformedBitmap.BeginInit();
    transformedBitmap.Source = source;
    transformedBitmap.Transform = new RotateTransform(90);
    transformedBitmap.EndInit();
    return transformedBitmap;

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public static byte[] SaveToJpeg(this BitmapSource source, int qualityLevel)
{
    if (source == null) throw new ArgumentNullException(nameof(source));

    using (var outputStream = new MemoryStream())
    {
        // WICのEncoderを利用してJpegファイルに保存する
        // System.Drawingパッケージの場合、8bit形式のJpegに対応していないため
        var encoder = new JpegBitmapEncoder { QualityLevel = qualityLevel };
        encoder.Frames.Add(BitmapFrame.Create(source));

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public static BitmapSource CreateFormJpeg(byte[] bytes)
{
    using (var stream = new MemoryStream(bytes))
    {
        var decoder = new JpegBitmapDecoder(stream, BitmapCreateOptions.None, BitmapCacheOption.OnLoad);
        return decoder.Frames[0];
    }
}

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public static BitmapImage Create(byte[] bytes)
{
    var result = new BitmapImage();

    using (var stream = new MemoryStream(bytes))
    {
        result.BeginInit();
        result.CacheOption = BitmapCacheOption.OnLoad;
        result.CreateOptions = BitmapCreateOptions.None;
        result.StreamSource = stream;

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protected override void OnInitialized()
{
    InitializeComponent();

    //NavigationService.NavigateAsync("MainPage?title=Hello%20from%20Xamarin.Forms");
    NavigationService.NavigateAsync("NavigationPage/MainPage?title=Hello%20from%20Xamarin.Forms");
}

protected override void RegisterTypes()
{

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<?xml version="1.0" encoding="utf-8" ?>
<ContentPage xmlns="http://xamarin.com/schemas/2014/forms"
             xmlns:x="http://schemas.microsoft.com/winfx/2009/xaml"
             xmlns:prism="clr-namespace:Prism.Mvvm;assembly=Prism.Forms"
             prism:ViewModelLocator.AutowireViewModel="True"
             x:Class="NavigationService.Views.SecondPage">
  <StackLayout Orientation="Vertical" HorizontalOptions="Center" VerticalOptions="Center">
    <Label Text="Second Page."/>
    <Button Text="Go Back." Command="{Binding GoBackCommand}"/>
  </StackLayout>

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public class SecondPageViewModel : BindableBase
{
    private readonly INavigationService _navigationService;
    public ICommand GoBackCommand { get; }
    public SecondPageViewModel(INavigationService navigationService)
    {
        _navigationService = navigationService;
        GoBackCommand = new DelegateCommand(() =>
        {
            _navigationService.GoBackAsync();