java.lang.ClassCastException：java.lang.String 无法转换为 java.lang.Long 错误 [重复]答案

【问题标题】：java.lang.ClassCastException: java.lang.String cannot be cast to java.lang.Long error [duplicate]java.lang.ClassCastException：java.lang.String 无法转换为 java.lang.Long 错误 [重复]
【发布时间】：2019-11-29 13:06:08
【问题描述】：

public class DBqueries {

   public static FirebaseFirestore firebaseFirestore = FirebaseFirestore.getInstance();
    public static List<CategoryModel> categoryModelList = new ArrayList<>();
    public static List<HomePageModel> homePageModelList = new ArrayList<>();

    public static void loadCategories(final CategoryAdapter categoryAdapter, final Context context){



        firebaseFirestore.collection("CATEGORIES").orderBy("index").get()
                .addOnCompleteListener(new OnCompleteListener<QuerySnapshot>() {
                    @Override
                    public void onComplete(@NonNull Task<QuerySnapshot> task) {
                        if (task.isSuccessful()){
                            for (QueryDocumentSnapshot documentSnapshot : task.getResult()){
                                categoryModelList.add(new CategoryModel(documentSnapshot.get("icon").toString(),documentSnapshot.get("categoryName").toString()));
                            }
                            categoryAdapter.notifyDataSetChanged();
                        }else {
                            String error = task.getException().getMessage();
                            Toast.makeText(context, error, Toast.LENGTH_SHORT).show();
                        }
                    }
                });
    }

    public static void loadFragmentData(final HomePageAdapter adapter, final Context context){
        firebaseFirestore.collection("CATEGORIES")
                .document("HOME")
                .collection("TOP_DEALS").orderBy("index").get()
                .addOnCompleteListener(new OnCompleteListener<QuerySnapshot>() {
                    @Override
                    public void onComplete(@NonNull Task<QuerySnapshot> task) {
                        if (task.isSuccessful()){
                            for (QueryDocumentSnapshot documentSnapshot : task.getResult()){

                                if ((long)documentSnapshot.get("view_type") == 0){
                                    List<SliderModel> sliderModelList = new ArrayList<>();
                                    long no_of_banners = (long) documentSnapshot.get("no_of_banners");
                                    for (long x = 1;x < no_of_banners + 1;x++){
                                        sliderModelList.add(new SliderModel((String) documentSnapshot.get("banner_"+x)
                                                ,documentSnapshot.get("banner_"+x+"_background").toString()));
                                    }
                                    homePageModelList.add(new HomePageModel(0,sliderModelList));

                                }else if ((long)documentSnapshot.get("view_type") == 1){
                                    homePageModelList.add(new HomePageModel(1, (String) documentSnapshot.get("strip_ad_banner"),
                                            documentSnapshot.get("background").toString()));

                                }else if ((long)documentSnapshot.get("view_type") == 2){

                                    List<WishlistModel> viewAllProductList = new ArrayList<>();
                                    List<HorizontalProductScrollModel> horizontalProductScrollModelList = new ArrayList<>();
                                    long no_of_products = (long) documentSnapshot.get("no_of_products");
                                    for (long x = 1;x < no_of_products + 1;x++){
                                        horizontalProductScrollModelList.add(new HorizontalProductScrollModel(documentSnapshot.get("product_ID_"+x).toString()
                                                ,documentSnapshot.get("product_image_"+x).toString()
                                                ,documentSnapshot.get("product_title_"+x).toString()
                                                ,documentSnapshot.get("product_subtitle_"+x).toString()
                                                ,documentSnapshot.get("product_price_"+x).toString()));


                                        viewAllProductList.add(new WishlistModel(documentSnapshot.get("product_image_"+x).toString()
                                                ,documentSnapshot.get("product_full_title_"+x).toString()
                                                ,(long)documentSnapshot.get("free_coupons_"+x)
                                                ,documentSnapshot.get("average_rating_"+x).toString()
                                                ,(long)documentSnapshot.get("total_ratings_"+x)
                                                ,documentSnapshot.get("product_price_"+x).toString()
                                                ,documentSnapshot.get("cutted_price_"+x).toString()
                                                ,(boolean)documentSnapshot.get("COD_"+x)));

                                    }
                                    homePageModelList.add(new HomePageModel(2,documentSnapshot.get("layout_title").toString()
                                            ,documentSnapshot.get("layout_background").toString(),
                                            horizontalProductScrollModelList,viewAllProductList));


                                }else if ((long)documentSnapshot.get("view_type") == 3){
                                    List<HorizontalProductScrollModel> gridLayoutModelList = new ArrayList<>();
                                    long no_of_products = (long) documentSnapshot.get("no_of_products");
                                    for (long x = 1;x < no_of_products + 1;x++){
                                        gridLayoutModelList.add(new HorizontalProductScrollModel(documentSnapshot.get("product_ID_"+x).toString()
                                                ,documentSnapshot.get("product_image_"+x).toString()
                                                ,documentSnapshot.get("product_title_"+x).toString()
                                                ,documentSnapshot.get("product_subtitle_"+x).toString()
                                                ,documentSnapshot.get("product_price_"+x).toString()));
                                    }
                                    homePageModelList.add(new HomePageModel(3,documentSnapshot.get("layout_title").toString()
                                            ,documentSnapshot.get("layout_background").toString(),
                                            gridLayoutModelList));

                                }
                            }
                            adapter.notifyDataSetChanged();
                        }else {
                            String error = task.getException().getMessage();
                            Toast.makeText(context, error, Toast.LENGTH_SHORT).show();
                        }
                    }
                });
    }
}

当我运行代码时，我得到了这个异常：

java.lang.ClassCastException: java.lang.String cannot be cast to java.lang.Long

还有其他方法可以转换结果吗？

【问题讨论】：

您是否阅读了错误信息？你了解什么是 ClassCastException 吗？你读过这个异常的javadoc吗？您是否阅读了异常附带的行号并指出了代码中引发此异常的确切行？
您可以在投射前使用 instance of 进行检查。
java.lang.ClassCastException: java.lang.String 无法在 com.shoppound.shoppound.DBqueries$2.onComplete(DBqueries.java:54) 处转换为 java.lang.Long
@DEKHOAURSIKHO 那么，DBqueries.java 的第 54 行是什么
@DEKHOAURSIKHO, please add your whole error stack trace 在你的问题中，不是在这里

标签： java

【解决方案1】：

使用 QueryDocumentSnapshot（继承自 DocumentSnapshot）提供的正确 API 方法，而不是（不正确）手动将结果转换为正确的类型。

例如： https://developers.google.com/android/reference/com/google/firebase/firestore/DocumentSnapshot.html#getLong(java.lang.String)

【讨论】：