Android - 获取基于孩子Firebase的推送密钥 [英] Android - Get push key based on a child Firebase

问题描述

  {
courses：{
业务：{
PushKey_1：{
courseC：B1111，
name：Business Year 1
}，
PushKey_2 ：{
courseC：B2222，
name：Business Year 2
}，
} 
} 
} 
  

我正在尝试基于子项检索推键。代码我正在尝试：

  String testCourseC =B2222; 
 String showCourseKey; 
 
 DatabaseReference mRef = FirebaseDatabase.getInstance（）。getReference（）。child（courses）。child（Business）; 
 mRef.addValueEventListener（new DataEventListener（）{
 @Override 
 public void onDataChange（DataSnapshot dataSnapshot）{
 for（DataSnapshot ds：dataSnapshot.getChildren（））{
 CourseDetails data = ds.getValue（CourseDetails.class）; 
 String compareC = data.getCourseC（）; 
 if（compareC.equals（testCourseC））{
 showCourseKey = dataSnapshot.getKey ）; 
} 
} 
} 
 
 @Override 
 public void onCancelled（DatabaseError databaseError）{
 
} 
}）; 
 
 textview1.setText（showCourseKey）; 
  

我的 CourseDetails class：

  public class CourseDetails {
 private String courseC; 
私人字符串名称; 
 $ b $ public CourseDetails（）{
} 
 
 public CourseDetails（String courseC，String name）{
 this.courseC = courseC; 
 this.name = name; 
} 
 
 public String getCourseC（）{
 return courseC; 
} 
 
 public void setCourseC（String courseC）{
 this.courseC = courseC; 
} 
 
 public String getName（）{
 return name; 
} 
 
 public void setName（String name）{
 this.name = name; 
 
 
 
 
 textview1应显示PushKey_2。如果代码是错误的，不应该textview1显示课程？
 
 
我得到了上面的代码NullPointerException。我已阅读文档，并经历了类似的问题，但仍然有这个错误。请不要介意我的愚蠢的问题
解决方案
我运行你的代码，没有得到 NullPointerException 。请发布堆栈跟踪。
 
 
 
我会指出看起来像是一个错误。
 
 
 
 p> 
 
 
  showCourseKey = dataSnapshot.getKey（）; 
  
应该是： 
 
 
  showCourseKey = ds.getKey（）; 
  
 
This is how my data looks like:
{
  "courses":{
    "Business":{
        "PushKey_1":{
                "courseC":"B1111",
                "name":"Business Year 1"
        },
        "PushKey_2":{
                "courseC":"B2222",
                "name":"Business Year 2"
        },
    }
  }
}
I'm trying to retrieve the push key based on a child. Code I'm trying now:
String testCourseC = "B2222";
String showCourseKey;

        DatabaseReference mRef = FirebaseDatabase.getInstance().getReference().child("courses").child("Business");
        mRef.addValueEventListener(new ValueEventListener() {
            @Override
            public void onDataChange(DataSnapshot dataSnapshot) {
                for (DataSnapshot ds : dataSnapshot.getChildren()){
                    CourseDetails data = ds.getValue(CourseDetails.class);
                    String compareC = data.getCourseC();
                    if (compareC.equals(testCourseC)){
                        showCourseKey = dataSnapshot.getKey();
                    }
                }
            }

            @Override
            public void onCancelled(DatabaseError databaseError) {

            }
        });

        textview1.setText(showCourseKey);
My CourseDetails class:
public class CourseDetails {
    private String courseC;
    private String name;

    public CourseDetails() {
    }

    public CourseDetails(String courseC, String name) {
        this.courseC = courseC;
        this.name = name;
    }

    public String getCourseC() {
        return courseC;
    }

    public void setCourseC(String courseC) {
        this.courseC = courseC;
    }

    public String getName() {
        return name;
    }

    public void setName(String name) {
        this.name = name;
    }
}
textview1 should display PushKey_2. If the code was wrong, shouldn't textview1 display "courses"?


I got NullPointerException from the code above. I have read the documentation and gone through similar questions, but still got this wrong. Please don't mind my silly question
解决方案
I run your code and do not get a NullPointerException.  Please post the stack trace.

I will point out what looks like an error.

This:
showCourseKey = dataSnapshot.getKey();
should be:
showCourseKey = ds.getKey();


                        
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