Как в DataGridView сделать ограничение на ввод символов?

private: System::Void dataGridView1_EditingControlShowing(System::Object^  sender, System::Windows::Forms::DataGridViewEditingControlShowingEventArgs^  e)
             {
 
              TextBox^ tb = (TextBox^)e->Control;
              tb->MaxLength = 4;
}

private: System::Void dataGridView1_EditingControlShowing(System::Object^  sender, System::Windows::Forms::DataGridViewEditingControlShowingEventArgs^  e)
             {
 
              TextBox^ tb = (TextBox^)e->Control;
              tb->MaxLength = 4;
            tb->KeyPress += gcnew KeyPressEventHandler(this,&Form1::tb_KeyPress);
        }
 
        void tb_KeyPress(Object^ sender, KeyPressEventArgs^ e)
        {           
            if (!(Char::IsDigit(e->KeyChar)||e->KeyChar == (char)Keys::Back))
                e->Handled = true;
        }

private: String ^ BaseName;
private: DataTable ^ Table;
private: DataSet ^ Set;
 
//...
 
#pragma region Windows Form Designer generated code
 
//...
 
private: System::Void Form1_Load (System::Object^  sender, System::EventArgs^  e) {
 BaseName  = "table1.xml"; Table = gcnew DataTable(); Set = gcnew DataSet();
 dataGridView1->DataSource = Table; Table->Columns->Add ("ФИО");
 for (int i=1; i<=17; i++) Table->Columns->Add(""+i);
 Table->Columns->Add("Итого");
 Set->Tables->Add(Table); dataGridView1->DataSource = Set;
 Table->TableName = "Успеваемость";
 if (IO::File::Exists(BaseName) == true) { 
  Set->ReadXml (BaseName);
 }
 dataGridView1->DataMember = "Успеваемость"; 
 for(int i=1; i<=17; i++) {
  dataGridView1->Columns[i]->Width = 25;
 }
}
 
private: System::Void Form1_FormClosing(System::Object^  sender, System::Windows::Forms::FormClosingEventArgs^  e) {
 Table->TableName = "Успеваемость";
 Set->WriteXml(BaseName);
}