如何在使用Parcelable的活动之间传递具有其他对象列表的对象？

Z时代
2024-01-10
分类：问答

我有一个叫做Order的对象，我想在这些活动之间传递。目前我正在使用Parcelable这样做。如何在使用Parcelable的活动之间传递具有其他对象列表的对象？

public class Order implements Parcelable { 
    private String email; 
    private Long timestamp; 
    private List<OrderItem> items; 
    public Order() { } 
    private Order(Parcel in) { 
     email = in.readString(); 
     timestamp = in.readLong(); 
    } 
    @Override 
    public void writeToParcel(Parcel dest, int flags) { 
     dest.writeString(email); 
     if (timestamp == null) { 
      dest.writeByte((byte) 0); 
     } else { 
      dest.writeByte((byte) 1); 
      dest.writeLong(timestamp); 
     } 
     dest.writeTypedList(items); 
    } 
    @Override 
    public int describeContents() { 
     return 0; 
    } 
    public static final Creator<Order> CREATOR = new Creator<Order>() { 
     @Override 
     public Order createFromParcel(Parcel in) { 
      return new Order(in); 
     } 
     @Override 
     public Order[] newArray(int size) { 
      return new Order[size]; 
     } 
    }; 
    // Getters 
    ... 
}

的items字段是实现Parcelable接口OrderItem的List对象。

public class OrderItem implements Parcelable { 
    private String orderedClothingId; 
    private int quantity; 
    public OrderItem() { } 
    public OrderItem(String orderedClothingId, int quantity) { 
     this.orderedClothingId = orderedClothingId; 
     this.quantity = quantity; 
    } 
    private OrderItem(Parcel in) { 
     orderedClothingId = in.readString(); 
     quantity = in.readInt(); 
    } 
    @Override 
    public void writeToParcel(Parcel dest, int flags) { 
     dest.writeString(orderedClothingId); 
     dest.writeInt(quantity); 
    } 
    @Override 
    public int describeContents() { 
     return 0; 
    } 
    public static final Creator<OrderItem> CREATOR = new Creator<OrderItem>() { 
     @Override 
     public OrderItem createFromParcel(Parcel in) { 
      return new OrderItem(in); 
     } 
     @Override 
     public OrderItem[] newArray(int size) { 
      return new OrderItem[size]; 
     } 
    }; 
}

我们从一个活动传递称为order的Order对象到另一个我执行以下操作：

Intent intent = new Intent(mContext, ActivityTwo.class); 
intent.addFlags(Intent.FLAG_ACTIVITY_CLEAR_TOP); 
intent.putExtra(ORDER_DETAIL_INTENT_EXTRA_KEY, order);    
mContext.startActivity(intent);

在ActivityTwo我收集像这样的Order对象：

Bundle data = getIntent().getExtras(); 
assert data != null; 
mOrder = data.getParcelable(ORDER_DETAIL_INTENT_EXTRA_KEY);

然而，当我在中记录Order对象中包含的items字段时它是null。如何在没有items列表为空的活动之间传递原始非空Order对象？

回答：

首先你错过dest = in.readTypedList(emptyList, CREATOR);

但第二也是更重要的，你需要写读阵列回/读取相同ammount的参数，因为你有一个如果你writeToParcel您在阅读时需要的一样：

private Order(Parcel in) { 
    email = in.readString(); 
    if(in.readByte() == 1) 
     timestamp = in.readLong(); //here to skip just like the writeToParcel 
    in.readTypedList(items = new ArrayList<OrderItem>(), OrderItem.CREATOR); 
} 
@Override 
public void writeToParcel(Parcel dest, int flags) { 
    dest.writeString(email); 
    if (timestamp == null) { 
     dest.writeByte((byte) 0); 
    } else { 
     dest.writeByte((byte) 1); 
     dest.writeLong(timestamp); 
    } 
    dest.writeTypedList(items); 
}