C# Richtextbox拖放与表单拖放不同

因此，我有一个richtextbox和一个表单，并为它们附加了一个拖放事件。它们的代码完全相同，我已经确定了，但是由于某种原因，richtextbox事件激活了文本更改事件。表单也会激活文本更改事件，但我在方法中有一个变量，我从拖动事件中调用该变量来阻止它。我尝试在不同的表单上复制它，但主要的问题是表单拖放事件的代码与richtextbox拖放事件完全相同。他们怎么可能不同呢？以下是投递代码：

    private void TestBox_DragEnter(object sender, DragEventArgs e)
            {
                if (e.Data.GetDataPresent(DataFormats.FileDrop))
                    e.Effect = DragDropEffects.Copy;
            }
    private async void TestBox_DragDrop(object sender, DragEventArgs e)
            {
                string filePath = ((string[])e.Data.GetData(DataFormats.FileDrop))[0];
                await AsyncStuff();
            }
    private async Task AsyncStuff() 
    {
        block = true;
        await OtherAsyncMethodThatActivatesTextChanged();
        block = false;
    }
        private bool block;
        private void TestBox_TextChanged(object sender, EventArgs e) 
        {
            if (block) return;
            MessageBox.Show("Text Changed called"); //Activates on the richtextbox drag, doesn't on the form
        }

我现在可以复制了，这是代码。我附加了表单拖放，并通过设计器输入事件

public partial class Form1 : Form
    {
        public Form1()
        {
            InitializeComponent();
            richTextBox1.AllowDrop = true;
            richTextBox1.TextChanged += TestBox_TextChanged;
            richTextBox1.DragDrop += TestBox_DragDrop;
            richTextBox1.DragEnter += TestBox_DragEnter;
            AllowDrop = true;
        }
        private void TestBox_DragEnter(object sender, DragEventArgs e)
        {
            if (e.Data.GetDataPresent(DataFormats.FileDrop))
                e.Effect = DragDropEffects.Copy;
        }
        private async void TestBox_DragDrop(object sender, DragEventArgs e)
        {
            string filePath = ((string[])e.Data.GetData(DataFormats.FileDrop))[0];
            await AsyncStuff();
        }
        private async Task AsyncStuff()
        {
            block = true;
            richTextBox1.AppendText("asd");
            block = false;
        }
        private bool block;
        private void TestBox_TextChanged(object sender, EventArgs e)
        {
            if (block) return;
            MessageBox.Show("Text Changed called"); //Activates on the richtextbox drag, doesn't on the form
        }

        private async void Form1_DragDrop(object sender, DragEventArgs e)
        {
            string filePath = ((string[])e.Data.GetData(DataFormats.FileDrop))[0];
            await AsyncStuff();
        }

        private void Form1_DragEnter(object sender, DragEventArgs e)
        {
            if (e.Data.GetDataPresent(DataFormats.FileDrop))
                e.Effect = DragDropEffects.Copy;
        }
    }