ParcelableArraylist可能会在片段中产生nullpointerexception

Question

我想将ArrayList<Palatte_Model>从一个Activity转移到另一个片段。我正在使用ParcelableArraylist。我附上了我的代码

public class Palette_Model  implements Parcelable{

    public String data_format_value;
    public int data_format_id;

    public Palette_Model(String data_format_value, int data_format_id) {
        this.data_format_value = data_format_value;
        this.data_format_id = data_format_id;

    }
    public String getData_format_value() {
        return data_format_value;
    }

    public void setData_format_value(String data_format_value) {
        this.data_format_value = data_format_value;
    }

    public int getData_format_id() {
        return data_format_id;
    }

    public void setData_format_id(int data_format_id) {
        this.data_format_id = data_format_id;
    }


    protected Palette_Model(Parcel in) {
        data_format_value = in.readString();
        data_format_id = in.readInt();
    }

    @Override
    public int describeContents() {
        return this.hashCode();
    }

    @Override
    public void writeToParcel(Parcel dest, int flags) {

        dest.writeString(data_format_value);
        dest.writeInt(data_format_id);

    }

    public void readfromParcel(Parcel source){
        data_format_id = source.readInt();
        data_format_value = source.readString();
    }

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

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

这里我附上了我的活动类代码。将arraylist发送到片段

Platte_fragment dFragment = new Platte_fragment();
                Bundle bundle = new Bundle();
                bundle.putParcelableArrayList("arraylist",  strQuestion);
                dFragment.setArguments(bundle);
              //  dFragment.show(fragmentManager, "array list");
                FragmentTransaction fts = getSupportFragmentManager().beginTransaction();
                fts.replace(R.id.questContFragId, dFragment);
                fts.addToBackStack(dFragment.getClass().getSimpleName());
                fts.commit();

在这里我提到了我的片段类代码：我从ArrayList获取Activity。它显示一个空值

ArrayList<Palette_Model> strQuestion ;

 strQuestion = new ArrayList<>();
         try {
             Bundle bundle = this.getArguments();
             strQuestion =  bundle.getParcelableArrayList("arraylist");

         }catch (NullPointerException e){
                Log.e("er",e.getMessage());
         }

所示方法可以产生NullpointerException。

Answer 1

我遇到了类似的问题。经过一些研究，我发现我的代码中的某个地方ArrayList<Type> list指向什么（NullpointerException）。

帮助我的是检查Bundle extras是否是null：

ArrayList<Category> categories = new ArrayList<Category>(); // you initialize it here
Bundle extras = getIntent().getExtras();
if (extras != null) {
       categories = extras.getParcelableArrayList("categories");
}

因此，如果检索到的数据为null，则不会将空指针附加到ArrayList。

有关NullPointerException的更多信息，请查看此link