当文本框嵌入到SplitContainer中时，无法使用鼠标选择文本框的文本

我有一个包含splitContainer的表单。在splitContainer的Panel2上，我添加了另一个表单，称为form2。在表格2中，我有一个文本框。

我可以编辑文本框，我的意思是我可以在文本框上打字。但是，我无法使用鼠标在文本框中选择文本。这是我的密码。

private void InitializeComponent()
        {
            this.splitContainer1 = new System.Windows.Forms.SplitContainer();
            this.textBox1 = new System.Windows.Forms.TextBox();
            this.form2 = new TestTextBox.Form2();
            this.splitContainer1.Panel1.SuspendLayout();
            this.splitContainer1.Panel2.SuspendLayout();
            this.splitContainer1.SuspendLayout();
            this.SuspendLayout();
            // 
            // splitContainer1
            // 
            this.splitContainer1.Dock = System.Windows.Forms.DockStyle.Fill;
            this.splitContainer1.Location = new System.Drawing.Point(0, 0);
            this.splitContainer1.Name = "splitContainer1";
            // 
            // splitContainer1.Panel1
            // 
            this.splitContainer1.Panel1.Controls.Add(this.textBox1);
            // 
            // splitContainer1.Panel2
            // 
            this.form2.TopLevel = false;
            this.splitContainer1.Panel2.Controls.Add(this.form2);
            this.splitContainer1.Size = new System.Drawing.Size(812, 347);
            this.splitContainer1.SplitterDistance = 438;
            this.splitContainer1.TabIndex = 0;
            // 
            // textBox1
            // 
            this.textBox1.Location = new System.Drawing.Point(94, 110);
            this.textBox1.Name = "textBox1";
            this.textBox1.Size = new System.Drawing.Size(213, 20);
            this.textBox1.TabIndex = 0;
            // 
            // form2
            // 
            this.form2.ClientSize = new System.Drawing.Size(362, 313);
            this.form2.Dock = System.Windows.Forms.DockStyle.Fill;
            this.form2.Location = new System.Drawing.Point(0, 0);
            this.form2.Name = "form2";
            this.form2.StartPosition = System.Windows.Forms.FormStartPosition.CenterParent;
            this.form2.Text = "Form2";
            // 
            // Form1
            // 
            this.AutoScaleDimensions = new System.Drawing.SizeF(6F, 13F);
            this.AutoScaleMode = System.Windows.Forms.AutoScaleMode.Font;
            this.ClientSize = new System.Drawing.Size(812, 347);
            this.Controls.Add(this.splitContainer1);
            this.Name = "Form1";
            this.Text = "Form1";
            this.splitContainer1.Panel1.ResumeLayout(false);
            this.splitContainer1.Panel1.PerformLayout();
            this.splitContainer1.Panel2.ResumeLayout(false);
            this.splitContainer1.ResumeLayout(false);
            this.ResumeLayout(false);
        }

form2有一个textBox。我无法使用鼠标选择此文本框的文本。任何知道这个问题的人，请帮帮我！