预加载只加载了一次，传值需要定时刷新

 mui.init();  
            mui.plusReady(function() {  
                mui("ul").on('tap', 'img', function() {  
                    var num = this.src; //获取点击该标签的值  
//                  alert(num); //用于测试，显示该值  
                    plus.storage.setItem('a', num);  
                    setTimeout(function() {  
                        var page = mui.preload({  
                            url: "second.html",  
                            id: "second",  
                        });  
                    }, 0.001);  
                    mui.openWindow({  
                        url: "second.html",  
                        id: "second",  
                    });  
                    plus.nativeUI.closeWaiting();  
                });  
            });