java - 空对象引用上的虚拟方法-Android中的错误

Question

我面临一个无法解决的空对象错误。我的应用程序编译得很好，但是当我使用“评价食物”功能时，应用程序崩溃并显示我链接的错误。我无法真正弄清楚为什么它应该是一个空对象，因为用户注册时会保存“Vorname”。也许我想识别“Vorname”的方式是错误的？如果您有任何想法我应该改变什么，请告诉我。谢谢，祝你有美好的一天！

如果您需要更多信息，请告诉我。

private UserProfil userProfil;

Food-Detail-Fragment（只是代码的一部分（发生错误的地方））

private void showDialogRating() {
        androidx.appcompat.app.AlertDialog.Builder builder=new androidx.appcompat.app.AlertDialog.Builder(getContext());
        builder.setTitle("Rating Food");
        builder.setMessage("Please fill in information");

        View itemView=LayoutInflater.from(getContext()).inflate(R.layout.layout_rating,null);
        Common.currentUser= userProfil;


        RatingBar ratingBar=(RatingBar)itemView.findViewById(R.id.rating_bar);
        EditText edt_comment=(EditText)itemView.findViewById(R.id.edt_comment);
        builder.setView(itemView);

        builder.setNegativeButton("CANCEL", (dialogInterface,i ) -> {
            dialogInterface.dismiss();
        });
        builder.setPositiveButton("OK", (dialogInterface, i) -> {
            CommentModel commentModel=new CommentModel();
            commentModel.setName(Common.currentUser.getVorname());
            commentModel.setUid(Common.currentUser.getUid());
            commentModel.setComment(edt_comment.getText().toString());
            commentModel.setRatingValue(ratingBar.getRating());
            Map<String,Object> serverTimeStamp =new HashMap<>();
            serverTimeStamp.put("timeStamp", ServerValue.TIMESTAMP);
            commentModel.setCommentTimeStamp(serverTimeStamp);

            foodDetailViewModel.setCommentModel(commentModel);

        });
        AlertDialog dialog=builder.create();
        dialog.show();

    }

用户资料

public class UserProfil {
    public String vorname;
    public String nachname;
    public String strasse;
    public String hnr;
    public String plz;
    public String stadt;
    public String land;
    public String uid;

    public UserProfil(){

    }


    public UserProfil(String Vorname, String Nachname,String Strasse,String HNr,String Plz,String Stadt,String Land,String Uid) {
        this.vorname = Vorname;
        this.nachname = Nachname;
        this.strasse= Strasse;
        this.hnr= HNr;
        this.plz=Plz;
        this.stadt=Stadt;
        this.land=Land;
        this.uid=Uid;

    }

    public String getVorname() {
       return vorname;
   }

    public void setVorname(String vorname) {
        this.vorname = vorname;
    }

    public String getNachname() {
        return nachname;
    }

    public void setNachname(String nachname) {
        this.nachname = nachname;
    }

    public void setStrasse(String strasse) {
        this.strasse = strasse;
    }

    public String getStrasse() {
        return strasse;
    }

    public void setHnr(String hnr) {
        this.hnr = hnr;
    }

    public String getHnr() {
        return hnr;
    }

    public void setPlz(String plz) {
        this.plz = plz;
    }

    public String getPlz() {
        return plz;
    }

    public void setStadt(String stadt) {
        this.stadt = stadt;
    }

    public String getStadt() {
        return stadt;
    }

    public void setLand(String land) {
        this.land = land;
    }

    public String getLand() {
        return land;
    }

    public void setUid(String uid) {
        this.uid = uid;
    }

    public String getUid() {
        return uid;
    }

通用 Java 类

public class Common {
    public static final String USER_PREFERENCES="Users";
    public static final String POPULAR_CATERGORY_REF = "MostPopular";
    public static final String BEST_DEALS_REF = "BestDeals";
    public static final int DEFAULT_COLUMN_COUNT = 0;
    public static final int FULL_WIDTH_COLUMN = 1;
    public static final String CATEGORY_REF = "Category";
    public static final String COMMENT_REF = "Comments";
    public static UserProfil currentUser;

    public static CategoryModel categorySelected;
    public static FoodModel selectedFood;
}

Logcat-错误

    java.lang.NullPointerException: Attempt to invoke virtual method 'java.lang.String com.example.login.UserProfil.getVorname()' on a null object reference
        at com.example.login.ui.fooddetail.FoodDetailFragment.lambda$showDialogRating$1$FoodDetailFragment(FoodDetailFragment.java:95)
        at com.example.login.ui.fooddetail.-$$Lambda$FoodDetailFragment$Wv1d4NkSDd8GTXyopN5Pa6I5Nkk.onClick(lambda)
        at androidx.appcompat.app.AlertController$ButtonHandler.handleMessage(AlertController.java:167)
        at android.os.Handler.dispatchMessage(Handler.java:102)
        at android.os.Looper.loop(Looper.java:234)
        at android.app.ActivityThread.main(ActivityThread.java:5526)
        at java.lang.reflect.Method.invoke(Native Method)
        at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:726)
        at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:616)

标签： javaandroidandroid-fragmentsandroid-activitynull

Answer 1

也许您忘记了初始化 userProfil 属性。

测试它：

private UserProfil userProfil = new UserProfil();