Android跨Fragment删除Firestore数据触发空指针异常问题

开发Android应用时，在Home Fragment的RecyclerView列表项中设置了心形心愿单复选框。用户点击可将商品加入Wishlist Fragment，再次点击需从Wishlist中删除。添加功能正常，但删除操作触发空指针异常。

核心代码 #

holder.wishlist.setOnCheckedChangeListener(new CompoundButton.OnCheckedChangeListener() {
    @Override
    public void onCheckedChanged(CompoundButton compoundButton, boolean b) {

        Boolean isCheck = compoundButton.isChecked();

        // 从Home Fragment添加商品到心愿单
        if(isCheck)
        {
            firebaseFirestore.collection("wishlistDetails").document(uid).set(wishMap).addOnCompleteListener(new OnCompleteListener<Void>() {
                @Override
                public void onComplete(@NonNull Task<Void> task) {
                    if (task.isSuccessful())
                    {
                        holder.wishlist.setButtonDrawable(R.drawable.ic_favorite_filled);
                        Toast.makeText(context, "item added to wishlist" + pos , Toast.LENGTH_SHORT).show();
                    }
                }
            }).addOnFailureListener(new OnFailureListener() {
                @Override
                public void onFailure(@NonNull Exception e) {}
            });

        // 从Home Fragment删除心愿单商品  
        }else {
            firebaseFirestore.collection("wishlistDetails").document(wishlist_models.get(position).getUid())
                    .delete()
                    .addOnCompleteListener(new OnCompleteListener<Void>() {
                        @Override
                        public void onComplete(@NonNull Task<Void> task) {
                            Toast.makeText(context, "item removed from wishlist", Toast.LENGTH_SHORT).show();
                        }
                    }).addOnFailureListener(new OnFailureListener() {
                @Override
                public void onFailure(@NonNull Exception e) {
                    Toast.makeText(context, e.getMessage(), Toast.LENGTH_SHORT).show();
                }
            });
        }
    }
});

Wishlist_Model类代码 #

public class Wishlist_Model {
    private List<String> images;
    private String name;
    private String email;
    private String delete;
    private String uid;

    public Wishlist_Model()  {}

    public Wishlist_Model(List<String> images, String name, String email, String delete, String uid) {
        this.images = images;
        this.name = name;
        this.email = email;
        this.delete = delete;
        this.uid = uid;
    }

    public String getName() { return name; }
    public void setName(String name) { this.name = name; }
    public String getEmail() { return email; }
    public void setEmail(String email) { this.email = email; }
    public String getDelete() { return delete; }
    public void setDelete(String delete) { this.delete = delete; }
    public List<String> getImages() { return images; }
    public void setImages(List<String> images) { this.images = images; }
    public String getUid() { return uid; }
    public void setUid(String uid) { this.uid = uid; }
}

Firestore集合结构 #

wishlistDetails集合以用户UID为文档ID，文档包含以下字段：

• delete：字符串类型
• email：字符串类型
• images：字符串列表类型
• name：字符串类型

错误信息 #

java.lang.NullPointerException: Attempt to invoke interface method 'java.lang.Object java.util.List.get(int)' on a null object reference

空指针异常根源是wishlist_models列表未初始化（为null），调用wishlist_models.get(position)时触发错误。

修复方案 #

1. 初始化列表：确保在RecyclerView适配器初始化前，wishlist_models已被实例化，例如：

   private List<Wishlist_Model> wishlist_models = new ArrayList<>();
   

2. 复用添加时的UID：删除操作无需从wishlist_models取UID，直接复用添加时使用的用户uid（与Firestore文档ID一致），修改删除逻辑：

   }else {
       firebaseFirestore.collection("wishlistDetails").document(uid)
               .delete()
               .addOnCompleteListener(new OnCompleteListener<Void>() {
                   @Override
                   public void onComplete(@NonNull Task<Void> task) {
                       if(task.isSuccessful()){
                           holder.wishlist.setButtonDrawable(R.drawable.ic_favorite_border); // 恢复空心图标
                           Toast.makeText(context, "item removed from wishlist", Toast.LENGTH_SHORT).show();
                       }
                   }
               }).addOnFailureListener(new OnFailureListener() {
           @Override
           public void onFailure(@NonNull Exception e) {
               Toast.makeText(context, e.getMessage(), Toast.LENGTH_SHORT).show();
               holder.wishlist.setChecked(true); // 失败时恢复选中状态
           }
       });
   }
   

3. 同步UI状态：删除成功后切换回空心心形图标；删除失败时将复选框重新设为选中，避免UI与实际数据状态不一致。

内容的提问来源于stack exchange，提问作者user20008723