Android Firebase从子节点检索数据

Question

我正在尝试从Firebase子节点获取数据.但它抛出Can't convert object of type java.lang.String to type uk.co.stableweb.geethika.model.DailyVerse异常.

这是我的Firebase数据库的结构.

这是代码.我正在使用Android Firebase新文档.

mRef = FirebaseDatabase.getInstance().getReference().child("daily_verse");
mRef.keepSynced(true);

ChildEventListener childEventListener = new ChildEventListener() {
    @Override
    public void onChildAdded(DataSnapshot dataSnapshot, String previousChildName) {
        Log.d("Child Event,Verse", dataSnapshot.getKey());

        dailyVerse = dataSnapshot.getValue(DailyVerse.class);

    }

    @Override
    public void onChildChanged(DataSnapshot dataSnapshot, String previousChildName) {
        Log.d("Child Event,Verse", "onChildChanged:" + dataSnapshot.getKey());

        dailyVerse = dataSnapshot.getValue(DailyVerse.class);
    }

    @Override
    public void onChildRemoved(DataSnapshot dataSnapshot) {

    }

    @Override
    public void onChildMoved(DataSnapshot dataSnapshot, String previousChildName) {

    }

    @Override
    public void onCancelled(DatabaseError databaseError) {
        Log.w("Firebase", "onCancelled", databaseError.toException());
        Toast.makeText(context, "Failed to load verse",
                Toast.LENGTH_SHORT).show();
    }
};

mRef.addChildEventListener(childEventListener);

和模型类.

public class DailyVerse {

    private String verse_title;
    private String verse_content;

    public String getVerseTitle() {
        return verse_title;
    }

    public void setVerseTitle(String verse_title) {
        this.verse_title = verse_title;
    }

    public String getVerseContent() {
        return verse_content;
    }

    public void setVerseContent(String verse_content) {
        this.verse_content = verse_content;
    }
}

和LogCat.

com.google.firebase.database.DatabaseException: Can't convert object of type java.lang.String to type uk.co.stableweb.geethika.model.DailyVerse
  at com.google.android.gms.internal.zzalq.zzd(Unknown Source)
  at com.google.android.gms.internal.zzalq.zzb(Unknown Source)
  at com.google.android.gms.internal.zzalq.zza(Unknown Source)
  at com.google.firebase.database.DataSnapshot.getValue(Unknown Source)
  at uk.co.stableweb.geethika.VerseActivityFragment$1.onChildAdded(VerseActivityFragment.java:63)
  at com.google.android.gms.internal.zzahh.zza(Unknown Source)
  at com.google.android.gms.internal.zzajh.zzctc(Unknown Source)
  at com.google.android.gms.internal.zzajk$1.run(Unknown Source)
  at android.os.Handler.handleCallback(Handler.java:739)
  at android.os.Handler.dispatchMessage(Handler.java:95)
  at android.os.Looper.loop(Looper.java:148)
  at android.app.ActivityThread.main(ActivityThread.java:5461)
  at java.lang.reflect.Method.invoke(Native Method)
  at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:726)
  at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:616)

但是,如果我更改数据库引用如下.并获取dataSnapshot值,它抓取数据.

mRef = FirebaseDatabase.getInstance().getReference("daily_verse");

testVal = (String) dataSnapshot.getValue();
Log.d("TEST", testVal);

V/FA: Activity resumed, time: 278033062
D/Child Event,Verse added: verse_content
D/TEST: ?????????? ?????? ???? ?????. ???? ?????????? ?? ????????? ??? ?????.
D/Child Event,Verse added: verse_title
D/TEST: ???????? 119:30

我认为可以使用HashMap获取这些值.但有评论说不再推荐.

Answer 1

请注意JSON中属性的名称以及Java代码中的字段/ getter.如果它们不匹配,Firebase客户端将无法匹配它们之间的值.

您的JSON有verse_title和verse_content,所以你的Java类必须是两种:

public class DailyVerse {
    public String verse_title;
    public String verse_content;    
}

或者:

public class DailyVerse {

    private String verse_title;
    private String verse_content;

    public String getVerse_title() {
        return verse_title;
    }

    public void setVerse_title(String verse_title) {
        this.verse_title = verse_title;
    }

    public String getVerse_content() {
        return verse_content;
    }

    public void setVerse_content(String verse_content) {
        this.verse_content = verse_content;
    }
}

从Firebase Android SDK 9.2开始,您还可以注释Java代码以映射到正确的JSON属性.因此,获得正确映射的第三种方法是:

public class DailyVerse {

    private String verse_title;
    private String verse_content;

    @PropertyName("verse_title")
    public String getVerseTitle() {
        return verse_title;
    }

    public void setVerseTitle(String verse_title) {
        this.verse_title = verse_title;
    }

    @PropertyName("verse_content")
    public String getVerseContent() {
        return verse_content;
    }

    public void setVerseContent(String verse_content) {
        this.verse_content = verse_content;
    }
}

我没有尝试过这个最新的版本,所以如果答案上有拼写错误,请告诉我.