How to restrict the number of items added in a dialog which has a multifield?

Current code is as below in my dialog.xml;

                          <field1

                                    jcr:primaryType="cq:Widget"

                                    name="./Field1"

                                    id="field1"

                                    fieldLabel="Field1"

                                    xtype="multifield">

                                  <fieldConfig

                                                jcr:primaryType="cq:Widget"

                                                xtype="compoundfield">    

                                    <items

                                                   jcr:primaryType="cq:WidgetCollection">

                                                   <subField1

                                                          jcr:primaryType="cq:Widget"

                                                          fieldLabel="subField1"

                                                          name="./subField1"

                                                          xtype="textfield"/>

                                                  <subField2

                                                           jcr:primaryType="cq:Widget"

                                                           fieldLabel="subField1"

                                                           name="./subField1"

                                                           xtype="textfield"/>

                                   </items>

                               </fieldConfig>

                        </field1>

Let's say I want to restrict the number of times I add the item in the dialog, what are the necessary changes to be made?