Disable combobox on Editable row Datagrid

[dayaners]

Good afternoon, I would like to disable a combobox in datagrid which is editable line with, that would be the only other editable fields.

this is my code:

Code:

columns:[[
            {field:'id',title:'Matérias',width:270,align:'left',
                    formatter:function(value,row){
                            return row.codmat;
                        },
					editor:{
                    type:'combobox',
                    options:{
                       url:'app/historico.app.php?Ajax=ListarCombobox&matricula='+matricula+'&idmat='+idmat, //combobox de materias
					    valueField:'id',
                        textField:'codmat',
                        required:true,
						
						onBeforeLoad: function(){
						var row = $('#tt').datagrid('getSelected');
						idmat = row.id;
						//alert(idmat);
					}
					}
                }
            },
            {field:'cargah',title:'CH',width:70,align:'center',editor:'numberbox'},
            {field:'ano1',title:'ANO 1',width:70,align:'center',editor:{type:'numberbox',options:{
				formatter:ver,
				parser:exibir
				}}
			},
            {field:'ano2',title:'ANO 2',width:70,align:'center',editor:{type:'numberbox',options:{
				formatter:ver,
				parser:exibir
				}}
			},
            {field:'ano3',title:'ANO 3',width:70,align:'center',editor:{type:'numberbox',options:{
				formatter:ver,
				parser:exibir
				}}
			},
			{field:'ano4',title:'ANO 4',width:70,align:'center',editor:{type:'numberbox',options:{
				formatter:ver,
				parser:exibir
				}}
			},
			{field:'ano5',title:'ANO 5',width:70,align:'center',editor:{type:'numberbox',options:{
				formatter:ver,
				parser:exibir
				}}
			},
			{field:'ano6',title:'ANO 6',width:70,align:'center',editor:{type:'numberbox',options:{
				formatter:ver,
				parser:exibir
				}}
			},
			{field:'ano7',title:'ANO 7',width:70,align:'center',editor:{type:'numberbox',options:{
				formatter:ver,
				parser:exibir
				}}
			},
			{field:'ano8',title:'ANO 8',width:70,align:'center',editor:{type:'numberbox',options:{
				formatter:ver,
				parser:exibir
				}}
			},
			{field:'ano9',title:'ANO 9',width:70,align:'center',editor:{type:'numberbox',options:{
				formatter:ver,
				parser:exibir
				}}
			},
        ]]
    });


var editIndex = undefined;
        function endEditing(){
            if (editIndex == undefined){return true}
			
            if ($('#tt').datagrid('validateRow', editIndex)){
				    $('#tt').datagrid('selectRow', editIndex)
                            .datagrid('beginEdit', editIndex);
                var ed = $('#tt').datagrid('getEditor', {index:editIndex,field:'id'});
				
                var descricao = $(ed.target).combobox('getText');
				
                $('#tt').datagrid('getRows')[editIndex]['codmat'] = descricao;
                $('#tt').datagrid('endEdit', editIndex);
                editIndex = undefined;
                return true;
            } else {
                return false;
            }
        }
        function onClickRow(index){ //começar edicao
			
            if (editIndex != index){
                if (saveit()){
					
                    $('#tt').datagrid('selectRow', index)
                            .datagrid('beginEdit', index);
                    editIndex = index;
                } else {
                    $('#tt').datagrid('selectRow', editIndex);
                }
            }
        }

sorry my bad english.
Thanks.