sencha touch中处置Android返回按钮事件

sencha touch中处理Android返回按钮事件
应用中只有一个NavigationView的情况：

// 处理一下android返回按钮		document.addEventListener("deviceready", onDeviceReady, false);		function onDeviceReady() {			document.addEventListener("backbutton", onBackKeyDown, false);		}		function onBackKeyDown() {			var canPop = false;			var id = Ext.Viewport.getActiveItem().id;			if (id.indexOf("login") != -1) {			} else if (id.indexOf("mainview") != -1) {				var mainview = Ext.Viewport.getActiveItem();				var length = mainview.getItems().length;				if (length > 2) {					canPop = true;				}			}			if (canPop) {				console.log("canPop");				ChinaFertilizer.app.getController("MainController").pop(1);			} else {				Ext.Msg.confirm("提示", "您确定要退出应用吗?", function(e) {					if (e == "yes") {						navigator.app.exitApp();					}				}, this);			}		}

在Ext.tab.Panel下有多个NavigationView的情况：

// 处理一下android返回按钮		document.addEventListener("deviceready", onDeviceReady, false);		function onDeviceReady() {			document.addEventListener("backbutton", onBackKeyDown, false);		}		function onBackKeyDown() {			var item = Ext.Viewport.getActiveItem();			var id = item.id;			if (id.indexOf("mainView") != -1) {				 var mainview = Ext.Viewport.getActiveItem();//				 var mainview = Ext.getCmp('moreView').getActiveItem();				 var length = mainview.getActiveItem().getItems().length;				 console.log("length = " + length);				 if(length > 2){					 if(app.viewId == 0){						 app.getController("phone.MyAppControllerP").pop(1);					 }else if(app.viewId == 1){						 app.getController("phone.TodoControllerP").pop(1);					 }else if(app.viewId == 2){						 app.getController("phone.AppCenterControllerP").pop(1);					 }else if(app.viewId ==3){						 app.getController("phone.MoreControllerP").pop(1);					 }				 }else{					 if (typeof WL === 'undefined') {						 Ext.Msg.confirm("提示", "您确定要退出应用吗?", function(e) {							 if (e == "yes") {								 navigator.app.exitApp();							 }						 }, this);					 } else {						 WL.SimpleDialog.show("提示", "您确定要退出应用吗?", [ {							 text : "确定",							 handler : function() {								 navigator.app.exitApp();							 }						 }, {							 text : "取消",							 handler : function() {							 }						 } ]);					 }					 				 }			 }else{				 if (typeof WL === 'undefined') {					 Ext.Msg.confirm("提示", "您确定要退出应用吗?", function(e) {						 if (e == "yes") {							 navigator.app.exitApp();						 }					 }, this);				 } else {					 WL.SimpleDialog.show("提示", "您确定要退出应用吗?", [ {						 text : "确定",						 handler : function() {							 navigator.app.exitApp();						 }					 }, {						 text : "取消",						 handler : function() {						 }					 } ]);				 }			 }