我有以下的火力地堡如何獲取Firebase android中所有孩子的列表?
這種模式,我嘗試使用下面的代碼
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) {
}
});
擺脫子節點職位的所有值,但我得到的錯誤java.lang.UnsupportedOperationException
。
在上面的場景我知道錯誤是因爲列表聲明最終,我想在onDataChangeMethod中分配值,所以是拋出錯誤,但如果我沒有聲明列表變量最後,那麼我不能訪問列表變量從內onDataChange()方法是如何解決這個
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;
}
}
錯誤日誌:
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。如果你可以發佈完整的日誌和'UserPostPojo'類,這將有所幫助。乾杯! –
嗨@AL。感謝回覆我在閱讀大量文章後發佈了代碼,我瞭解到firebase操作是異步操作,因此嘗試將onDataChange方法內的值分配給全局變量會在聲明全局最終您不能分配任何東西之後拋出異常以使全局變量最終生效在這裏,所以修復是做回調,當你想分配你必須使用回調分配,但我不知道如何使用回調可以請你解釋一下,如果這一切都使得無論如何 –
這是解決你的問題:https:// stackoverflow.com/a/45328201/5973946 –