使用.net core3.0 正式版创建Winform程序

.NET Core Windows Forms 可视化设计器在将来一定是未来的Visual Studio 2019更新的一部分，但目前来说，想要可视化设计器，需要一个预发布的Visual Studio扩展。

   public partial class Form1 : Form
    {
        public Form1()
        {
            InitializeComponent();
        }

        private void button1_Click(object sender, EventArgs e)
        {
            MessageBox.Show("你好，这是一个.net core的Winform程序", "提示信息", 
                MessageBoxButtons.OK, MessageBoxIcon.Information | MessageBoxIcon.Asterisk);
        }

           
        private ImageList imageList = new ImageList();
        private void Form1_Load(object sender, EventArgs e)
        {
            var image = Image.FromFile(Path.Combine(Application.StartupPath, "SplashScreen.png"));
            if(image != null)
            {
                this.pictureBox1.Image = image;
            }

            imageList.Images.Clear();
            var iconPath = Path.Combine(Application.StartupPath, "icons");
            var fileNames = Directory.GetFiles(iconPath, "*.ico");
            foreach(string file in fileNames)
            {
                imageList.Images.Add(file, Image.FromFile(file));
            }
            this.treeView1.ImageList = imageList;
            foreach(TreeNode node in this.treeView1.Nodes)
            {
                SetNodeImage(node);
            }

            this.button1.Image = imageList.Images[2];
        }

        private void SetNodeImage(TreeNode node)
        {
            foreach (TreeNode subNode in node.Nodes)
            {
                subNode.ImageIndex = subNode.Level;
                subNode.SelectedImageIndex = subNode.Level;
                SetNodeImage(subNode);
            }
        }