Question

我正在尝试从Firebase获取一些数据。我的Firebase结构如下：

"groups": {
   group-key (random key generated by firebase): {
      "creationDate": 
      "dropbox": 
      "endDate": 
      "evernote": 
      "googleDocs": 
      "members": {
               "0": user 1
               "1": user 2 
               "2": user 3 etc....
      }
     "projectName": 
     "subject": 
   }
}

我正在尝试使用以下代码从groups子级中提取所有日期：

private List<DataService> grouplist;

mDatabase = FirebaseDatabase.getInstance();
mDBRef = mDatabase.getReference().child("groups");
grouplist = new ArrayList<>();

@Override
protected void onStart() {
    super.onStart();

grouplist.clear();

        mDBRef.addChildEventListener(new ChildEventListener() {
        @Override
        public void onChildAdded(@NonNull DataSnapshot dataSnapshot, @Nullable String s) {


            String creationDate = (String) dataSnapshot.child("creationDate").getValue();
            String dropbox = (String) dataSnapshot.child("dropbox").getValue();
            String endDate = (String) dataSnapshot.child("endDate").getValue();
            String evernote = (String) dataSnapshot.child("evernote").getValue();
            String googleDocs = (String) dataSnapshot.child("googleDocs").getValue();
            String members = (String) dataSnapshot.child("members").getValue();
            String projectName = (String) dataSnapshot.child("projectName").getValue();
            String subject = (String) dataSnapshot.child("subject").getValue();

            DataService dataService = new DataService();
            dataService.setCreationDate(creationDate);
            dataService.setDropbox(dropbox);
            dataService.setEndDate(endDate);
            dataService.setEvernote(evernote);
            dataService.setGoogleDocs(googleDocs);
            dataService.setmembers(members);
            dataService.setProjectName(projectName);
            dataService.setSubject(subject);

            grouplist.add(dataService);

            Log.d(TAG, String.valueOf(grouplist));

        }         
    });
}

还有我的DataSerivice.java

public class DataService {
public String subject;
public String projectName;
public String endDate;
public String members;
public String creationDate;
public String dropbox;
public String evernote;
public String googleDocs;

public DataService() {
}

public DataService(String subject, String projectName, String endDate, String members, String creationDate, String dropbox, String evernote, String googleDocs) {
    this.subject = subject;
    this.projectName = projectName;
    this.endDate = endDate;
    this.members = members;
    this.creationDate = creationDate;
    this.dropbox = dropbox;
    this.evernote = evernote;
    this.googleDocs = googleDocs;
}

public String getCreationDate() {
    return creationDate;
}

public void setCreationDate(String creationDate) {
    this.creationDate = creationDate;
}

public String getDropbox() {
    return dropbox;
}

public void setDropbox(String dropbox) {
    this.dropbox = dropbox;
}

public String getEvernote() {
    return evernote;
}

public void setEvernote(String evernote) {
    this.evernote = evernote;
}

public String getGoogleDocs() {
    return googleDocs;
}

public void setGoogleDocs(String googleDocs) {
    this.googleDocs = googleDocs;
}

public String getSubject() {
    return subject;
}

public void setSubject(String subject) {
    this.subject = subject;
}

public String getProjectName() {
    return projectName;
}

public void setProjectName(String projectName) {
    this.projectName = projectName;
}

public String getEndDate() {
    return endDate;
}

public void setEndDate(String endDate) {
    this.endDate = endDate;
}

public String getmembers() {
    return members;
}

public void setmembers(String members) {
    this.members = members;
}

}

但是我遇到了这个错误：

java.lang.ClassCastException：无法将java.lang.Long强制转换为java.lang.String

我的猜测是问题出在“成员”子并从那里获取用户。我是在正确的轨道上吗/出什么问题了，还是有更好的方法来做到这一点？感谢所有帮助。

Firebase screenshot

Answer 1

尝试使用这种方式

public void onChildAdded(@NonNull DataSnapshot dataSnapshot, @Nullable String s) {
            DataService creationDate = dataSnapshot.getValue(DataService.class);
            grouplist.add(dataService);
            Log.d(TAG, String.valueOf(grouplist));
        }

您正面临错误，因为您试图将值对象转换为字符串类。因此，您只需使用上面规定的代码，就可以简单地使用每个toString()值方法作为

来调用getValue()方法

String creationDate = dataSnapshot.child("creationDate").getValue().toString(); //convert land value to String value not into the String class object

您还需要将String member更改为List<User> member，并更改其数据类型为List的setter和getter方法。

记住：我假设User是一个具有用户数据的类。如果它是一个简单的String，则可以使用String代替User

Answer 2

代替此

        String creationDate = (String) dataSnapshot.child("creationDate").getValue();
        String dropbox = (String) dataSnapshot.child("dropbox").getValue();
        String endDate = (String) dataSnapshot.child("endDate").getValue();
        String evernote = (String) dataSnapshot.child("evernote").getValue();
        String googleDocs = (String) dataSnapshot.child("googleDocs").getValue();
        String members = (String) dataSnapshot.child("members").getValue();
        String projectName = (String) dataSnapshot.child("projectName").getValue();
        String subject = (String) dataSnapshot.child("subject").getValue();

这样做

        String creationDate = dataSnapshot.child("creationDate").getValue().toString();
        String dropbox = dataSnapshot.child("dropbox").getValue().toString();
        String endDate = dataSnapshot.child("endDate").getValue().toString();
        String evernote = dataSnapshot.child("evernote").getValue().toString();
        String googleDocs = dataSnapshot.child("googleDocs").getValue().toString();
        String members = dataSnapshot.child("members").getValue().toString();
        String projectName = dataSnapshot.child("projectName").getValue().toString();
        String subject = dataSnapshot.child("subject").getValue().toString();

toString（）用于将任何值转换为字符串。您不能像执行操作一样将任何内容强制转换为字符串。

此代码

        DataService dataService = new DataService();
        dataService.setCreationDate(creationDate);
        dataService.setDropbox(dropbox);
        dataService.setEndDate(endDate);
        dataService.setEvernote(evernote);
        dataService.setGoogleDocs(googleDocs);
        dataService.setmembers(members);
        dataService.setProjectName(projectName);
        dataService.setSubject(subject);
        grouplist.add(dataService);

可以替换为此

        DataService dataService = new DataService(subject, projectName, endDate, members, creationDate, dropbox, evernote, googleDocs);
        grouplist.add(dataService);

或者这个

        grouplist.add(new DataService(subject, projectName, endDate, members, creationDate, dropbox, evernote, googleDocs));

因为您已经为此类创建了构造函数。

Answer 3

问题是您的模型类中有creationDate个类型为String的集合，而在数据库中，creationDate是一个long。要解决此问题，请在模型类中将属性的类型从String更改为long：

public long creationDate;

还请将相应的setter和getter更改为：

public long getCreationDate() {
    return creationDate;
}

public void setCreationDate(long creationDate) {
    this.creationDate = creationDate;
}

构造函数也应这样更改：

public DataService(String subject, String projectName, String endDate, String members, long creationDate, String dropbox, String evernote, String googleDocs) {
    this.subject = subject;
    this.projectName = projectName;
    this.endDate = endDate;
    this.members = members;
    this.creationDate = creationDate;
    this.dropbox = dropbox;
    this.evernote = evernote;
    this.googleDocs = googleDocs;
}

最后，只需更改以下代码行：

String creationDate = (String) dataSnapshot.child("creationDate").getValue();

到

long creationDate = dataSnapshot.child("creationDate").getValue(Long.class);

从Firebase提取数据导致崩溃

3 个答案: