Question

早安，

我试图从Firebase中获取数据，但不幸的是，它加载了Intent但崩溃了。

这是我的代码

这是我生成的主要Java类。

Voter_SSC_President.java

 DatabaseReference databaseReferenceSSCPres;

ListView listViewSSCPresident;

List<SSC_Presidents> sscPresList;

@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_voter__ssc__president);

    databaseReferenceSSCPres = FirebaseDatabase.getInstance().getReference("candidate");

    listViewSSCPresident = findViewById(R.id.listViewArtists);

    sscPresList = new ArrayList<>();



}

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

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

            sscPresList.clear();

            for (DataSnapshot SSCPresSnapshot : dataSnapshot.getChildren())
            {
                SSC_Presidents SSCPres = SSCPresSnapshot.getValue(SSC_Presidents.class);

                sscPresList.add(SSCPres);
            }

            SSCPresLists adapter = new SSCPresLists(Voter_SSC_President.this, sscPresList);
            listViewSSCPresident.setAdapter(adapter);
        }

        @Override
        public void onCancelled(DatabaseError databaseError) {

        }
    });
}

这是Java类，倾向于从Firebase获取数据

SSC_Presidents.java

 String candidate_platform;
String college_id;
String council_id;
String first_name;
String last_name;
String middle_name;
String partylist_id;
String position_id;
String school_year;
String student_id;

public SSC_Presidents()
{

}

public String getCandidate_platform() {
    return candidate_platform;
}

public String getCollege_id() {
    return college_id;
}

public String getCouncil_id() {
    return council_id;
}

public String getFirst_name() {
    return first_name;
}

public String getLast_name() {
    return last_name;
}

public String getMiddle_name() {
    return middle_name;
}

public String getPartylist_id() {
    return partylist_id;
}

public String getPosition_id() {
    return position_id;
}

public String getSchool_year() {
    return school_year;
}

public String getStudent_id() {
    return student_id;
}

这是我的充气机Java类。

SSCPresList.java

private Activity context;
private List<SSC_Presidents> SSC_PresidentsList;

public  SSCPresLists(Activity context, List<SSC_Presidents> SSC_PresidentsList )
{
    super(context, R.layout.listview_voter_ssc_president, SSC_PresidentsList);
    this.context = context;
    this.SSC_PresidentsList = SSC_PresidentsList;
}

@NonNull
@Override
public View getView(int position, @Nullable View convertView, @NonNull ViewGroup parent) {
    LayoutInflater inflater = context.getLayoutInflater();

    View listViewItem = inflater.inflate(R.layout.listview_voter_ssc_president, null, false);

    TextView textViewLast_name = (TextView) listViewItem.findViewById(R.id.list_last_name);
    TextView textViewFirst_middle_name = (TextView) listViewItem.findViewById(R.id.list_first_middle_name);
    TextView textViewPartylist = (TextView) listViewItem.findViewById(R.id.list_partylist);
    TextView textPlatform = (TextView) listViewItem.findViewById(R.id.list_platform);

    SSC_Presidents sscPresidents = SSC_PresidentsList.get(position);

    textViewLast_name.setText(sscPresidents.getLast_name());
    textViewFirst_middle_name.setText(sscPresidents.getFirst_name()+", "+sscPresidents.getMiddle_name());
    textViewPartylist.setText(sscPresidents.getPartylist_id());
    textPlatform.setText(sscPresidents.getCandidate_platform());

    return listViewItem;
}

这是我的Firebase结构。 Firebase Structure

我在youtube教程中模仿了此代码。当我运行他的代码版本时，我获得了成功。但是当我修改它时，我没有成功

预先感谢您的回答。

编辑。

这是我的Logcat

09-23 21：28：00.119 17620-17620 / com.example.vj.plmonlinevoting

E/AndroidRuntime: FATAL EXCEPTION: main
    Process: com.example.vj.plmonlinevoting, PID: 17620
    java.lang.NullPointerException: Attempt to invoke virtual method 'void android.widget.ListView.setAdapter(android.widget.ListAdapter)' on a null object reference
        at com.example.vj.plmonlinevoting.Voter_SSC_President$1.onDataChange(Voter_SSC_President.java:60)
        at com.google.android.gms.internal.zzegf.zza(Unknown Source)
        at com.google.android.gms.internal.zzeia.zzbyc(Unknown Source)
        at com.google.android.gms.internal.zzeig.run(Unknown Source)
        at android.os.Handler.handleCallback(Handler.java:739)
        at android.os.Handler.dispatchMessage(Handler.java:95)
        at android.os.Looper.loop(Looper.java:135)
        at android.app.ActivityThread.main(ActivityThread.java:5318)
        at java.lang.reflect.Method.invoke(Native Method)
        at java.lang.reflect.Method.invoke(Method.java:372)
        at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:922)
        at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:717)

从Firebase获取数据到ListView崩溃

0 个答案: