Question

我一直在尝试从firebase数据库更新，但每次我这样做都会给我一个错误...这是我的Firebase数据库：

mDatabaseGroup.addValueEventListener(new ValueEventListener() {
        @Override
        public void onDataChange(DataSnapshot dataSnapshot) {

            final String team_a = (String) dataSnapshot.child("Team_A").child("team_name").getValue();
            final long team_ad = (long) dataSnapshot.child("Team_A").child("d").getValue();
            final long team_al = (long) dataSnapshot.child("Team_A").child("l").getValue();
            final long team_ap = (long) dataSnapshot.child("Team_A").child("p").getValue();
            final long team_aw = (long) dataSnapshot.child("Team_A").child("w").getValue();
            final long team_apts = (long) dataSnapshot.child("Team_A").child("pts").getValue();
            final String team_b = (String) dataSnapshot.child("Team_B").child("team_name").getValue();
            final long team_bd = (long) dataSnapshot.child("Team_B").child("d").getValue();
            final long team_bl = (long) dataSnapshot.child("Team_B").child("l").getValue();
            final long team_bp = (long) dataSnapshot.child("Team_B").child("p").getValue();
            final long team_bw = (long) dataSnapshot.child("Team_B").child("w").getValue();
            final long team_bpts = (long) dataSnapshot.child("Team_B").child("pts").getValue();
            final String team_c = (String) dataSnapshot.child("Team_C").child("team_name").getValue();
            String team_d = (String) dataSnapshot.child("Team_D").child("team_name").getValue();}

        @Override
        public void onCancelled(DatabaseError databaseError) {

        }
    });

这是我遇到的错误：

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

这是我的stackTrace：

D/NativeCrypto: ssl=0x56944ba8 sslWrite buf=0x427180f8 len=99 write_timeout_millis=0
D/NativeCrypto:  sslNotify, appData=0x5807ff10 ret=1
D/NativeCrypto:  sslSelect, appData=0x5807ff10 woken up by a token
D/NativeCrypto:  sslSelect, appData=0x5807ff10 read ret=1 
D/SQLiteDatabase: beginTransaction()
D/SQLiteDatabase: endTransaction()
D/AndroidRuntime: Shutting down VM
W/dalvikvm: threadid=1: thread exiting with uncaught exception (group=0x4187ece0)
W/dalvikvm: threadid=1: uncaught exception occurred
W/System.err: java.lang.ClassCastException: java.lang.String cannot be cast to java.lang.Long
W/System.err:     at com.example.zack.admin.ViewFixtureActivity$1.onDataChange(ViewFixtureActivity.java:85)
W/System.err:     at com.google.android.gms.internal.zzaih.zza(Unknown Source)
W/System.err:     at com.google.android.gms.internal.zzajh.zzctc(Unknown Source)
W/System.err:     at com.google.android.gms.internal.zzajk$1.run(Unknown Source)
W/System.err:     at android.os.Handler.handleCallback(Handler.java:808)
W/System.err:     at android.os.Handler.dispatchMessage(Handler.java:103)
W/System.err:     at android.os.Looper.loop(Looper.java:193)
W/System.err:     at android.app.ActivityThread.main(ActivityThread.java:5299)
W/System.err:     at java.lang.reflect.Method.invokeNative(Native Method)
W/System.err:     at java.lang.reflect.Method.invoke(Method.java:515)
W/System.err:     at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:829)
W/System.err:     at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:645)
W/System.err:     at dalvik.system.NativeStart.main(Native Method)
W/dalvikvm: threadid=1: calling UncaughtExceptionHandler
E/AndroidRuntime: FATAL EXCEPTION: main
                  Process: com.example.zack.admin, PID: 26018
                  java.lang.ClassCastException: java.lang.String cannot be cast to java.lang.Long
                      at com.example.zack.admin.ViewFixtureActivity$1.onDataChange(ViewFixtureActivity.java:85)
                      at com.google.android.gms.internal.zzaih.zza(Unknown Source)
                      at com.google.android.gms.internal.zzajh.zzctc(Unknown Source)
                      at com.google.android.gms.internal.zzajk$1.run(Unknown Source)
                      at android.os.Handler.handleCallback(Handler.java:808)
                      at android.os.Handler.dispatchMessage(Handler.java:103)
                      at android.os.Looper.loop(Looper.java:193)
                      at android.app.ActivityThread.main(ActivityThread.java:5299)
                      at java.lang.reflect.Method.invokeNative(Native Method)
                      at java.lang.reflect.Method.invoke(Method.java:515)
                      at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:829)
                      at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:645)
                      at dalvik.system.NativeStart.main(Native Method)

如果有人知道另一种在firebase上更新的方式，也欢迎。

Answer 1

如果您想读取类型为long的单个值（即/ Groups / -Kh2GRPKiuQdePCubLi0 / A / Team_A / d），您可以编写如下代码：

FirebaseDatabase.getInstance().getReference("Groups/-Kh2GRPKiuQdePCubLi0/A/Team_A/d").addValueEventListener(new ValueEventListener() {
        @Override
        public void onDataChange(DataSnapshot dataSnapshot) {
            Long team_ad = dataSnapshot.getValue(Long.class);
        }

        @Override
        public void onCancelled(DatabaseError databaseError) {

        }
    });

如果从参考文献中读取（Groups / -Kh2GRPKiuQdePCubLi0 / A），您可以编写如下代码：

// Create a model class for your dataSnapshot
public static class Team {
    public long d;
    public long l;
    public long p;
    public long pts;
    public String team_name;
    public long w;

    public Team() {
        // Default constructor required for calls to DataSnapshot.getValue(Team.class)
    }
}
// Read from database
FirebaseDatabase.getInstance().getReference("Groups/-Kh2GRPKiuQdePCubLi0/A").addValueEventListener(new ValueEventListener() {
        @Override
        public void onDataChange(DataSnapshot dataSnapshot) {
            for(DataSnapshot childDataSnapShot: dataSnapshot.getChildren()){
                Team team = childDataSnapShot.getValue(Team.class);
                switch (childDataSnapShot.getKey())
                {
                    case "Team_A":
                        final String team_a = team.team_name;
                        final long team_ad = team.d;
                        final long team_al = team.l;
                        final long team_ap = team.p;
                        final long team_aw = team.w;
                        final long team_apts = team.pts;
                        break;
                    case "Team_B":
                        final String team_b = team.team_name;
                        final long team_bd = team.d;
                        final long team_bl = team.l;
                        final long team_bp = team.p;
                        final long team_bw = team.w;
                        final long team_bpts = team.pts;
                        break;
                    case "Team_C":
                        final String team_c = team.team_name;
                        final long team_cd = team.d;
                        final long team_cl = team.l;
                        final long team_cp = team.p;
                        final long team_cw = team.w;
                        final long team_cpts = team.pts;
                        break;
                    default:
                        break;
                }
            }
        }

        @Override
        public void onCancelled(DatabaseError databaseError) {
            // Getting Team failed, log a message
            Log.w(LOG_TAG, "loadTeam:onCancelled ", databaseError.toException());
        }
    });
}

参考：https://firebase.google.com/docs/database/android/read-and-write#read_and_write_data

Answer 2

如果使用String.valueOf()

进行投射，请在该位置使用(String)

String.valueOf(dataSnapshot.child("Team_C").child("team_name").getValue());

Answer 3

首先，确保您的DatabaseReference mDatabaseGroup位于/Groups/Key/A的正确位置，以便从数据库中获取正确的值。

其次，试试

final long team_ad = dataSnapshot.child("Team_A").child("d").getValue(Long.class);

从firebase数据库更新很长时间

3 个答案: