火力地堡。一旦（）：用成功和失败回调

Question

我在我的角度，应用

$scope.retrieveProjectData = function() { 
     $scope.projectNumberNoChange = false; 

     // Only retrieve Data if the ProjectNumber changed 
     if (currentlySelectedProjectNumber != $scope.feedback.projectNumber.content) { 
      currentlySelectedProjectNumber = $scope.feedback.projectNumber.content; 

      // Go to database-reference based on the projectNumber 
      var projectsRef = firebaseDatabaseRef.child("projects"); 
      var currentChild = projectsRef.child(currentlySelectedProjectNumber); 

      // retrieve data once and fill $scope.feedback 
      currentChild.once("value", 
       // If the project is found 
       function (dataSnapshot) { 
        // Fill selectedProject and hand over to writeDataFromSelectedProject() 
        var selectedProject = dataSnapshot.val(); 

        // Fill $scope.feedback 
        writeDataFromSelectedProject(selectedProject); 
       }, 

       // If no data is found 
       function() { 
        console.log("No data found"); 
       }); 
     } 
     // If the projectNumber didn't change, the projectNumberNoChangeMessage will be shown 
     else { 
      $scope.projectNumberNoChange = true; 
     } 
    }; 

用户有关于他的项目数（比如加载一些数据的可能性以下功能：名称，电子邮件，电话），以使用户填写表格的速度更快。

在部分：

currentChild.once("value", 
       // If the project is found 
       function (dataSnapshot) { 
        // Fill selectedProject and hand over to writeDataFromSelectedProject() 
        var selectedProject = dataSnapshot.val(); 

        // Fill $scope.feedback 
        writeDataFromSelectedProject(selectedProject); 
       }, 

       // If no data is found 
       function() { 
        console.log("No data found"); 
       }); 

只有第一个回调函数被调用，即使projectNumber没有被发现。如何使用所述的“failureCallbackOrContext”？

感谢您花时间！

Answer 1

问题解决了。我刚刚检查了dataSnapshot.val（）方法，以便让一个对象或null！