GSON反序列化与InstanceCreator嵌套对象 [英] Gson deserializing nested objects with InstanceCreator

问题描述

我有一个名为 PageItem 类，它有一个构造函数一个上下文作为参数：

I have a class named PageItem, which has a constructor that takes a Context as parameter:

PageItem(Context context)
{
    super(context);
    this.context = context;
}

PageItem 具有以下属性：

private int id; 
private String Title; 
private String Description; 
public Newsprovider newsprovider; 
public Topic topic;

Newsprovider 和主题其他类我的应用程序，并有下面的构造函数：

Newsprovider and Topic are other classes of my application and have the following constructors:

Newsprovider (Context context)
{
    super(context);
    this.context = context;
}

Topic (Context context)
{
    super(context);
    this.context = context;
}

PageItem ， Newsprovider 和主题是子类 SQLiteOpenHelper 。

我要反序列化与GSON PageItem 阵列，所以我写了：

I want to deserialize PageItem array with Gson, so I wrote:

GsonBuilder gsonBuilder = new GsonBuilder();
gsonBuilder.registerTypeAdapter(PageItem.class, new PageItemInstanceCreator(context));
Gson gson = gsonBuilder.create();
Pageitem pis[] = gson.fromJson(s, PageItem[].class);

与 PageItemInstanceCreator 定义为：

public class PageItemInstanceCreator implements InstanceCreator<PageItem>
    {
        private Context context;

        public PageItemInstanceCreator(Context context)
        {
            this.context = context;
        }

        @Override
        public PageItem createInstance(Type type)
        {
            PageItem pi = new PageItem(context);
            return pi; 
        }
}

在调试时， PageItem 实例有正确的MainActivity为背景而
但其 newsprovider 成员变量具有上下文= NULL。

When debugging, a PageItem instance has correctly "MainActivity" as context while but its newsprovider member variable has context = null.

GSON创建使用正确的构造 PageItem 对象，但它使用默认参数的构造函数创建 Newsprovider 实例。我该如何解决这个问题？

Gson created PageItem object using the right constructor but it created Newsprovider instance using the default parameterless constructor. How can I fix this?

推荐答案

只需添加一个新的 InstanceCreator 派生类 NewsProvider 是这样的：

Just add a new InstanceCreator derived class for NewsProvider like this:

public class NewsProviderInstanceCreator implements InstanceCreator<NewsProvider>
    {
        private int context;

        public NewsProviderInstanceCreator(int context)
        {
            this.context = context;
        }

        @Override
        public NewsProvider createInstance(Type type)
        {
            NewsProvider np = new NewsProvider(context);
            return np; 
        }

}

和它注册到 GsonBuilder 像你已经这样做，是这样的：

and register it into the GsonBuilder like you have already done, like this:

GsonBuilder gsonBuilder = new GsonBuilder();
gsonBuilder.registerTypeAdapter(PageItem.class, new PageItemInstanceCreator(context));
gsonBuilder.registerTypeAdapter(NewsProvider.class, new NewsProviderInstanceCreator(context));
Gson gson = gsonBuilder.create();
PageItem pis[] = gson.fromJson(s, PageItem[].class);

重复它也为主题类。

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