XAMLを使わないWPF入門39「コードビハイドによるドラックアンドドロップで画像表示」

<Project Sdk="Microsoft.NET.Sdk">

  <PropertyGroup>
    <OutputType>WinExe</OutputType>
    <TargetFramework>net8.0-windows</TargetFramework>
    <Nullable>enable</Nullable>
    <ImplicitUsings>enable</ImplicitUsings>
    <UseWPF>true</UseWPF>
  </PropertyGroup>

</Project>

using System;
using System.Windows;

namespace NoXAML39DragAndDrop
{
    public class App : Application
    {
        [STAThread]
        public static void Main(string[] args)
        {
            var app = new App();
            app.Run();
        }

        protected override void OnStartup(StartupEventArgs e)
        {
            base.OnStartup(e);
            var win = new MainWindow();
            win.Show();
        }
    }
}

using System.Windows;

[assembly:ThemeInfo(
    ResourceDictionaryLocation.None,            //where theme specific resource dictionaries are located
                                                //(used if a resource is not found in the page,
                                                // or application resource dictionaries)
    ResourceDictionaryLocation.SourceAssembly   //where the generic resource dictionary is located
                                                //(used if a resource is not found in the page,
                                                // app, or any theme specific resource dictionaries)
)]

using System;
using System.IO;
using System.Linq;
using System.Windows.Media;
using System.Windows.Media.Imaging;

namespace NoXAML39DragAndDrop;

public static class ImageLoader
{
    public static readonly string[] SupportedExts =
    {
    ".png", ".jpg", ".jpeg", ".bmp", ".tif", ".tiff", ".gif", ".webp"
    };

    public static bool IsSupported(string path)
        => File.Exists(path) && SupportedExts.Contains(Path.GetExtension(path).ToLowerInvariant());

    public static BitmapSource Load(string path)
    {
        var bi = new BitmapImage();
        bi.BeginInit();
        bi.CacheOption = BitmapCacheOption.OnLoad; // ファイルロック回避
        bi.UriSource = new Uri(Path.GetFullPath(path));
        bi.EndInit();
        bi.Freeze();

        // 描画の安定性を優先して BGRA32 に揃える
        var src = new FormatConvertedBitmap(bi, PixelFormats.Bgra32, null, 0);
        src.Freeze();
        return src;
    }
}

using System.Windows;
using System.Windows.Controls;
using System.Windows.Input;
using System.Windows.Media;

namespace NoXAML39DragAndDrop;
public class MainWindow : Window
{
    TextBlock _hint;
    Image _image;
    public MainWindow()
    {
        Title = "DnDで画像表示（コードビハインド / NoXAML）";
        Width = 1000; Height = 700;

        // ルート
        var root = new Grid();
        root.RowDefinitions.Add(new RowDefinition { Height = GridLength.Auto });
        root.RowDefinitions.Add(new RowDefinition { Height = new GridLength(1, GridUnitType.Star) });
        Content = root;

        // ヘッダ（使い方メモ）
        var header = new TextBlock
        {
            Margin = new Thickness(8),
            Text = "中央の枠に画像ファイルをドラッグ＆ドロップしてください。Ctrl+Cで画像をコピーできます。",
            TextWrapping = TextWrapping.Wrap
        };
        Grid.SetRow(header, 0);
        root.Children.Add(header);

        // 表示エリア
        var _dropBorder = new Border { BorderBrush = Brushes.LightGray, BorderThickness = new Thickness(1), Margin = new Thickness(8) };

        var displayGrid = new Grid();

        _image = new Image
        {
            Stretch = Stretch.None,               // 等倍表示（スクロールで全体を確認）
            SnapsToDevicePixels = true
        };

        var scroll = new ScrollViewer
        {
            Content = _image,
            HorizontalScrollBarVisibility = ScrollBarVisibility.Auto,
            VerticalScrollBarVisibility = ScrollBarVisibility.Auto
        };
        displayGrid.Children.Add(scroll);

        _hint = new TextBlock
        {
            Text = "ここに画像をドラッグ＆ドロップ",
            Foreground = Brushes.Gray,
            HorizontalAlignment = HorizontalAlignment.Center,
            VerticalAlignment = VerticalAlignment.Center
        };
        displayGrid.Children.Add(_hint);

        _dropBorder.Child = displayGrid;

        // D&D
        _dropBorder.AllowDrop = true;
        _dropBorder.DragOver += OnDragOver;
        _dropBorder.Drop += OnDrop;

        Grid.SetRow(_dropBorder, 1);
        root.Children.Add(_dropBorder);

        // Ctrl+C で表示中画像をクリップボードへ
        PreviewKeyDown += OnPreviewKeyDown;
    }

    private void OnDragOver(object sender, DragEventArgs e)
    {
        bool ok = false;
        if (e.Data.GetDataPresent(DataFormats.FileDrop))
        {
            var files = (string[])e.Data.GetData(DataFormats.FileDrop);
            ok = files.Any(ImageLoader.IsSupported);
        }
        e.Effects = ok ? DragDropEffects.Copy : DragDropEffects.None;
        e.Handled = true;
    }

    private void OnDrop(object sender, DragEventArgs e)
    {
        if (!e.Data.GetDataPresent(DataFormats.FileDrop)) return;

        var files = ((string[])e.Data.GetData(DataFormats.FileDrop))
            .Where(ImageLoader.IsSupported)
            .ToArray();

        var first = files.FirstOrDefault();
        if (first is null) return;

        try
        {
            _image.Source = ImageLoader.Load(first);
            _hint.Visibility = Visibility.Collapsed;
        }
        catch
        {
            // 必要に応じてエラーダイアログなど
        }
    }

    private void OnPreviewKeyDown(object? sender, KeyEventArgs e)
    {
        if (e.Key == Key.C && (Keyboard.Modifiers & ModifierKeys.Control) == ModifierKeys.Control)
        {
            if (_image.Source is System.Windows.Media.Imaging.BitmapSource bmp)
            {
                Clipboard.SetImage(bmp);
            }
        }
    }
}