最大化ボタン無効化

MainWindow.xaml

<Window
    x:Class="SampleApp.MainWindow"
    xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
    xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
    xmlns:d="http://schemas.microsoft.com/expression/blend/2008"
    xmlns:local="clr-namespace:SampleApp"
    xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006"
    Title="MainWindow"
    Width="300"
    Height="200"
    ResizeMode="CanResizeWithGrip"
    SourceInitialized="Window_SourceInitialized"
    mc:Ignorable="d">
    <Grid />
</Window>

MainWindow.xaml.cs

using System;
using System.Runtime.InteropServices;
using System.Windows;

namespace SampleApp
{
    /// <summary>
    /// MainWindow.xaml の相互作用ロジック
    /// </summary>
    public partial class MainWindow : Window
    {
        /// <summary>
        /// ウィンドウに関するデータを取得
        /// </summary>
        /// <param name="hWnd"></param>
        /// <param name="nIndex"></param>
        /// <returns></returns>
        [DllImport("user32.dll")]
        private static extern int GetWindowLong(IntPtr hWnd, int nIndex);

        /// <summary>
        /// ウィンドウの属性を変更
        /// </summary>
        /// <param name="hWnd"></param>
        /// <param name="nIndex"></param>
        /// <param name="dwNewLong"></param>
        /// <returns></returns>
        [DllImport("user32.dll")]
        private static extern int SetWindowLong(IntPtr hWnd, int nIndex, int dwNewLong);

        /// <summary>
        /// ウィンドウスタイル
        /// </summary>
        private const int GWL_STYLE = -16;

        /// <summary>
        /// 最大化ボタン
        /// </summary>
        private const int WS_MAXIMIZEBOX = 0x0001_0000; // C#7より前の場合は 0x00010000

        public MainWindow()
        {
            InitializeComponent();
        }

        /// <summary>
        /// 初期化時
        /// </summary>
        /// <param name="sender"></param>
        /// <param name="e"></param>
        private void Window_SourceInitialized(object sender, EventArgs e)
        {
            IntPtr hwnd = new System.Windows.Interop.WindowInteropHelper((Window)sender).Handle;
            int value = GetWindowLong(hwnd, GWL_STYLE);
            SetWindowLong(hwnd, GWL_STYLE, (int)(value & ~WS_MAXIMIZEBOX));
        }
    }

}