创建RichTextBox的右键菜单（比较基础的东西了）

懒得说一大堆，直接上代码

        private void 复制ToolStripMenuItem_Click(object sender, EventArgs e)
        {
            this.contextMenuStrip1.SourceControl.Select();//先获取焦点，防止点两下才运行
            RichTextBox rtb = (RichTextBox)this.contextMenuStrip1.SourceControl;
            rtb.Copy();
        }

        private void 粘贴ToolStripMenuItem_Click(object sender, EventArgs e)
        {
            this.contextMenuStrip1.SourceControl.Select();
            RichTextBox rtb = (RichTextBox)this.contextMenuStrip1.SourceControl;
            rtb.Paste();
        }

        private void 剪切ToolStripMenuItem_Click(object sender, EventArgs e)
        {
            this.contextMenuStrip1.SourceControl.Select();
            RichTextBox rtb = (RichTextBox)this.contextMenuStrip1.SourceControl;
            rtb.Cut();
        }

        private void 删除ToolStripMenuItem_Click(object sender, EventArgs e)
        {
            this.contextMenuStrip1.SourceControl.Select();
            RichTextBox rtb = (RichTextBox)this.contextMenuStrip1.SourceControl;
            rtb.SelectedText = "";
        }

        private void 全选ToolStripMenuItem_Click(object sender, EventArgs e)
        {
            this.contextMenuStrip1.SourceControl.Select();
            RichTextBox rtb = (RichTextBox)this.contextMenuStrip1.SourceControl;
            rtb.SelectAll();
        }

        private void 撤销ToolStripMenuItem_Click(object sender, EventArgs e)
        {
            this.contextMenuStrip1.SourceControl.Select();
            RichTextBox rtb = (RichTextBox)this.contextMenuStrip1.SourceControl;
            rtb.Undo();
        }