var MainStageName = "main";

function AppAssistant (appController) {
}

AppAssistant.prototype.handleLaunch = function (launchParams) {
  // Look for an existing main stage by name.
  var stageProxy = this.controller.getStageProxy(MainStageName);
  var stageController = this.controller.getStageController(MainStageName);
 
  //如果etStageController()和 getStageProxy()都返回空， 则说明stage还没有被创建或者已创建但不可用。
  if (stageProxy) {
      // 如果stage已存在，就把它显示到界面最前面
      // 如果只有proxy（没有stageController）, 那stage已经被focus了。
      if (stageController) {
          stageController.window.focus();
      }
  } else {
      // Create a callback function to set up the new main stage
      // after it is done loading. It is passed the new stage controller
      // as the first parameter.
      var pushMainScene = function(stageController) {
          stageController.pushScene("main");
      };
      var stageArguments = {name: "MainStageName", lightweight: true};
      // 最后一个参数指定stage类型
      this.controller.createStageWithCallback(stageArguments, pushMainScene, "card");
  }
};