Question

对不起我的noob问题。我有一个名为Card的类。如果我使用另一个扩展名为BookHeader的Card的类。为什么我不能在List中使用它？这是我的代码：

    package com.peomtime.tosca.peomtime.Databse;

import android.content.Context;

import it.gmariotti.cardslib.library.internal.Card;
import it.gmariotti.cardslib.library.internal.CardHeader;

/**
 * Created by CrazyVirus on 2015-02-06.
 */
public class PartHeader extends Card {
    private String Title;
    private String ID;
    private String BookID;
    private Context context;
    private CardHeader header;

    public void setBookID(String BookID)
    {
        this.BookID = BookID;
    }
    public String getBookID(){return this.BookID;}

    public void setTitle(String Title)
    {
        this.Title = Title;
        header.setTitle(Title);
        this.addCardHeader(header);
    }
    public String getTitle(){return this.Title;}

    public void setID(String ID)
    {
        this.ID = ID;
    }
    public String getID(){return this.ID;}

    public PartHeader(Context c){
        super(c);
        this.context =c;
        header = new CardHeader(context);

    }

    public Card getCard(){

        return this;
    }
}

因为它显示我的课程扩展了Card.So我如何在这些代码中使用它

List<PartHeader> BookPartList = db.getAllBookParts(BookID);
BookPartAdaptet mBookPartAdapter = new BookPartAdaptet(this, BookPartList );

这里是BookPartAdaptet

  public BookPartAdaptet(Context context, List<Card> cards) {


    super(context, cards);
    data=cards;
   // inflater = ( LayoutInflater )context.getSystemService(Context.LAYOUT_INFLATER_SERVICE);
  //  activity = context.getApplicationContext();

}

我在这一行得到错误

BookPartAdaptet mBookPartAdapter = new BookPartAdaptet(this, BookPartList );

表示BookPartList myst属于List<Card>类型而不是List<PartHeader >

我认为因为扩展类我可以使用它作为父类型？如果我不能怎么做呢？谢谢你的帮助。对不起我的noob问题:(

Answer 1

我想你想尝试这样的事情：

public BookPartAdaptet(Context context, List<? extends Card> cards) {
    // ...
}

Answer 2

您应该将BookPartAdaptet的定义更改为以下内容，以便您可以传递任何子类的列表

public BookPartAdaptet(Context context, List<? extends Card> cards){
}

扩展类不是父类型？

2 个答案: