java将数据从firebase传递到对象类

Question

我遇到的问题是，当我设置Text-textview时，总会出现空指针异常，因此我无法将Text设置到我的视图

我认为对象没有填充getData方法中的字段。如何解决这个问题

我正在遵循这个步骤https://firebase.google.com/docs/firestore/query-data/listen#listen_to_multiple_documents_in_a_collection和这个Parcelable object passing from 安卓 activity to fragment

这是安卓 studio控制台的错误输出

E/AndroidRuntime: FATAL EXCEPTION: main
    Process: com.my.plkbi, PID: 24337
    java.lang.NullPointerException: Attempt to invoke virtual method 'java.lang.String com.my.plkbi.Layanan.getSyarat()' on a null object reference
        at com.my.plkbi.SubMainFragment.onCreateView(SubMainFragment.java:78)
        at 安卓x.fragment.app.Fragment.performCreateView(Fragment.java:2600)
        at 安卓x.fragment.app.FragmentManagerImpl.moveToState(FragmentManagerImpl.java:881)
        at 安卓x.fragment.app.FragmentManagerImpl.moveFragmentToExpectedState(FragmentManagerImpl.java:1238)
        at 安卓x.fragment.app.FragmentManagerImpl.moveToState(FragmentManagerImpl.java:1303)
        at 安卓x.fragment.app.BackStackRecord.executeOps(BackStackRecord.java:439)
        at 安卓x.fragment.app.FragmentManagerImpl.executeOps(FragmentManagerImpl.java:2079)
        at 安卓x.fragment.app.FragmentManagerImpl.executeOpsTogether(FragmentManagerImpl.java:1869)
        at 安卓x.fragment.app.FragmentManagerImpl.removeRedundantOperationsAndExecute(FragmentManagerImpl.java:1824)
        at 安卓x.fragment.app.FragmentManagerImpl.execPendingActions(FragmentManagerImpl.java:1727)
        at 安卓x.fragment.app.FragmentManagerImpl$2.run(FragmentManagerImpl.java:150)
        at 安卓.os.Handler.handleCallback(Handler.java:751)
        at 安卓.os.Handler.dispatchMessage(Handler.java:95)
        at 安卓.os.Looper.loop(Looper.java:154)
        at 安卓.app.ActivityThread.main(ActivityThread.java:6119)
        at java.lang.reflect.Method.invoke(Native Method)
        at com.安卓.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:886)
        at com.安卓.internal.os.ZygoteInit.main(ZygoteInit.java:776)

编辑：添加构造函数从其他对象添加对象，我遵循以下How do I copy an object in Java? 这是关于字段数据库和Parcelable的对象

public class Layanan implements Parcelable {
    private String Nama;
    private String Syarat;
    private String Langkah;
    private String Lampiran;

    public Layanan(){
        //this("connect to internet", "connect to internet", "connect to internet", "connect to internet");
    }

//Constructor to add value from another object
    public Layanan(Layanan another) {
        this.nama = another.nama;
        this.syarat = another.syarat;
        this.langkah = another.langkah;
        this.lampiran = another.lampiran;
        this.deskripsi = another.deskripsi;
    }

    protected Layanan(Parcel in) {
        Nama = in.readString();
        Syarat = in.readString();
        Langkah = in.readString();
        Lampiran = in.readString();
    }

    public static final Creator<Layanan> CREATOR = new Creator<Layanan>() {
        @Override
        public Layanan createFromParcel(Parcel in) {
            return new Layanan(in);
        }

        @Override
        public Layanan[] newArray(int size) {
            return new Layanan[size];
        }
    };

    public static Layanan newInstance() {

        Bundle args = new Bundle();

        Layanan fragment = new Layanan();
        fragment.setArguments(args);
        return fragment;
    }

    private void setArguments(Bundle args) {

    }

    public String getNama() {
        return Nama;
    }

    public String getSyarat() {
        return Syarat;
    }

    public void setSyarat(String syarat) {
        Syarat = syarat;
    }

    public String getLangkah() {
        return Langkah;
    }

    public void setNama(String nama) {
        Nama = nama;
    }

    public void setLangkah(String langkah) {
        Langkah = langkah;
    }

    public String getLampiran() {
        return Lampiran;
    }

    public void setLampiran(String lampiran) {
        Lampiran = lampiran;
    }

    @Override
    public int describeContents() {
        return 0;
    }

    @Override
    public void writeToParcel(Parcel dest, int flags) {
        dest.writeString(Nama);
        dest.writeString(Syarat);
        dest.writeString(Langkah);
        dest.writeString(Lampiran);
    }
}

这就是我从Firebase获取数据的方式，它在活动中

Layanan UP;
Layanan GU;
Layanan LS;


    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);

        if(savedInstanceState == null) {
            //initMF();
            MainFragment homeFragment = MainFragment.newInstance();

            Bundle extras = new Bundle();


            getData("UP");
            Log.d(TAG, "This is the value name of " + UP.getNama()); //Output: This is the value name of null
            extras.putParcelable(UPParcelable, UP);
            if (UP.getSyarat()!=null) Log.d(TAG, "Value Added"); 
            if (UP.getSyarat()==null) Log.d(TAG, "Value not Added"); //Output: Value not Added

            homeFragment.setArguments(extras);
            getSupportFragmentManager().beginTransaction().add(R.id.main_activity, homeFragment).commit();
        }
...
...
    public void getData(final String p){
        mFirebase.collection("panduan_layanan")
                .whereEqualTo("nama", p)
                .addSnapshotListener(new EventListener<QuerySnapshot>() {

                    @Override
                    public void onEvent(@Nullable QuerySnapshot value, @Nullable FirebaseFirestoreException e) {
                        if (e != null){
                            Log.w(TAG, "onEvent:error", e);
                            return;
                        }
                        Layanan newLayanan = new Layanan();
                        for (QueryDocumentSnapshot doc : value) {
                            if (doc.get("nama") != null && doc.get("syarat") != null && doc.get("langkah") != null && doc.get("lampiran")!= null){
                                newLayanan.setNama(doc.getString("nama"));
                                newLayanan.setLampiran(doc.getString("lampiran"));
                                newLayanan.setLangkah(doc.getString("langkah"));
                                newLayanan.setSyarat(doc.getString("syarat"));
                                Log.d(TAG, "Update data: Success" + p);
                                Log.d(TAG, "This is the " + p + " syarat" + newLayanan.getSyarat());
                                if (newLayanan.getSyarat() != null) Log.d(TAG, "new layanan is" + newLayanan.getNama()); //new layanan isUP, it is work too
                            }
                        }
                        if (p.equals("UP")) UP = new Layanan(newLayanan);
                        Log.d(TAG, "the" + UP.getNama());  //Output theUP so it is work in here
                        if (p.equals("GU")) GU = new Layanan(newLayanan);
                        if (p.equals("LS")) LS = new Layanan(newLayanan);
                    }
                });
    }
...

多谢各位

Answer 1

您不能这样做，因为firebase异步执行该块。因此，该字段不会像Frank的评论所说的那样立即获得价值