我有以下的火力地堡如何获取Firebase android中所有孩子的列表?
这种模式,我尝试使用下面的代码
databasePostsReference =
FirebaseDatabase.getInstance().getReference().child("posts");
final List<UserPostPOJO> list = Collections.EMPTY_LIST;
databasePostsReference.addValueEventListener(new ValueEventListener() {
@Override
public void onDataChange(DataSnapshot dataSnapshot) {
for(DataSnapshot snapshot : dataSnapshot.getChildren()){
Log.d(TAG, "onDataChange: entered list adding");
UserPostPOJO post = snapshot.getValue(UserPostPOJO.class);
list.add(post);
}
}
@Override
public void onCancelled(DatabaseError databaseError) {
}
});
摆脱子节点职位的所有值,但我得到的错误java.lang.UnsupportedOperationException
。
在上面的场景我知道错误是因为列表声明最终,我想在onDataChangeMethod中分配值,所以是抛出错误,但如果我没有声明列表变量最后,那么我不能访问列表变量从内onDataChange()方法是如何解决这个
public class UserPostPOJO {
String uid;
Double elevation;
String uri;
String feel;
public UserPostPOJO() {
}
public UserPostPOJO(String uid, Double elevation, String uri, String feel) {
this.uid = uid;
this.elevation = elevation;
this.uri = uri;
this.feel = feel;
}
public String getUid() {
return uid;
}
public void setUid(String uid) {
this.uid = uid;
}
public Double getElevation() {
return elevation;
}
public void setElevation(Double elevation) {
this.elevation = elevation;
}
public String getUri() {
return uri;
}
public void setUri(String uri) {
this.uri = uri;
}
public String getFeel() {
return feel;
}
public void setFeel(String feel) {
this.feel = feel;
}
}
错误日志:
05-08 22:19:49.706 6421-6421/redeyes17.com.abhi.android.iamat
D/recentfragment: onDataChange: entered list adding
05-08 22:19:49.726 6421-6421/redeyes17.com.abhi.android.iamat
E/AndroidRuntime: FATAL EXCEPTION: main
Process: redeyes17.com.abhi.android.iamat, PID: 6421
java.lang.UnsupportedOperationException
at java.util.AbstractList.add(AbstractList.java:404)
at java.util.AbstractList.add(AbstractList.java:425)
at redeyes17.com.abhi.android.iamat.UI.tabs
.RecentFragment$1.onDataChange(RecentFragment.java:78)
at com.google.android.gms.internal.zzbpx.zza(Unknown Source)
at com.google.android.gms.internal.zzbqx.zzZT(Unknown Source)
at com.google.android.gms.internal.zzbra$1.run(Unknown Source)
at android.os.Handler.handleCallback(Handler.java:739)
at android.os.Handler.dispatchMessage(Handler.java:95)
at android.os.Looper.loop(Looper.java:158)
at android.app.ActivityThread.main(ActivityThread.java:7230)
at java.lang.reflect.Method.invoke(Native Method)
at com.android.internal.os.ZygoteInit$MethodAndArgsCaller
.run(ZygoteInit.java:1230)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:1120)
嗨Abhilash。如果你可以发布完整的日志和'UserPostPojo'类,这将有所帮助。干杯! –
嗨@AL。感谢回复我在阅读大量文章后发布了代码,我了解到firebase操作是异步操作,因此尝试将onDataChange方法内的值分配给全局变量会在声明全局最终您不能分配任何东西之后抛出异常以使全局变量最终生效在这里,所以修复是做回调,当你想分配你必须使用回调分配,但我不知道如何使用回调可以请你解释一下,如果这一切都使得无论如何 –
这是解决你的问题:https:// stackoverflow.com/a/45328201/5973946 –