如何把一个向量成intent.extra？ [英] How to put a Vector into an intent.extra?

问题描述

我已经开始写了Android的一个小应用程序。它看起来很漂亮，但有一件事我不明白。

我已经创建了活性的新意图，我添加了一个序列化的载体 intent.putExtra（钥匙，向量）。在所谓的b活动我这样做：矢量＆lt; ItemModel＆GT;项目=（矢量＆lt; ItemModel＆GT;）。getIntent（）getExtras（）getSerializable（钥匙）。此行引起 ClassCastException异常。有谁知道为什么吗？请大家帮帮我： - ）

下面是两个活动的源头 ItemModel ：

ItemModel：

 公共类ItemModel实现了java.io.Serializable {
    私有静态最后长的serialVersionUID = -1772392719565658730L;
    公众诠释ID;
    公共字符串名称;
    公共字符串数量;
    公众诠释状态;

}
 

ShoppingListActivity（A）：

 公共无效onClickItems（最终​​查看V）{
        最终意向意图=新的意图（这一点，ItemListActivity.class）;

        矢量＆lt; ItemModel＆GT; V1 =新矢量＆lt; ItemModel＆GT;（）;
        ItemModel项目=新ItemModel（）;

        item.name =Tomaten;
        item.quantity =400克;
        item.id = 12;
        item.status = 0;
        v1.add（项目）;

        项目=新ItemModel（）;
        item.name =Bohnen;
        item.quantity =150克;
        item.id = 13;
        item.status = 0;
        v1.add（项目）;

        项目=新ItemModel（）;
        item.name =Schokolade;
        item.quantity =5 Tafeln;
        item.id = 17;
        item.status = 0;
        v1.add（项目）;

        intent.putExtra（ShoppingList，第一版）;

        startActivity（意向）;
 

ItemListActivity（B）：

 公共类ItemListActivity延伸活动{
    @覆盖
    公共无效的onCreate（包savedInstanceState）{
        super.onCreate（savedInstanceState）;
        的setContentView（R.layout.item）;
        ListView控件列表=（ListView控件）findViewById（R.id.ITEMSLIST）;
        最终捆绑额外= getIntent（）getExtras（）。
        矢量＆lt; ItemModel＆GT;项=（矢量＆lt; ItemModel＆GT）extras.getSerializable（ShoppingList）;
        ArrayList的＆LT; HashMap的＆LT;字符串，对象＆gt;＆GT; itemsList =新的ArrayList＆LT; HashMap的＆LT;字符串，对象＆gt;＆GT;（）;
        HashMap的＆LT;字符串，对象＆gt; itemMap =新的HashMap＆LT;字符串，对象＆gt;（）;
}
 

解决方案

任何实现列表和序列化的内部变成了一个ArrayList。因此，它可能会去作为一个载体，但它出来作为ArrayList。它可能会更好的治疗它只是一个List＆LT;>在推杆和getter两端

作为一般规则，不要使用向量两种。所有的方法是同步的，这使得它比一个ArrayList效率较低。

I've started to write a small app for android. It looks very nice, but there is one thing I don't understand.

I've created a new intent in the activity A and I've added a serialized vector intent.putExtra("key", vector). On the called activity B I'm doing this: Vector<ItemModel> items = (Vector<ItemModel>) getIntent().getExtras().getSerializable("key"). This line causes a ClassCastException. Does anyone know why? Please help me :-)

Here is the source of the two activities and of the ItemModel:

ItemModel:

public class ItemModel implements java.io.Serializable {
    private static final long serialVersionUID = -1772392719565658730L;
    public int id;
    public String name;
    public String quantity;
    public int status;

}

ShoppingListActivity (A):

   public void onClickItems(final View v){
        final Intent intent = new Intent(this,ItemListActivity.class);

        Vector<ItemModel> v1 = new Vector<ItemModel>();
        ItemModel item = new ItemModel();

        item.name = "Tomaten";
        item.quantity = "400g";
        item.id = 12;
        item.status = 0;
        v1.add(item);

        item = new ItemModel();
        item.name = "Bohnen";
        item.quantity = "150g";
        item.id = 13;
        item.status = 0;
        v1.add(item);

        item = new ItemModel();
        item.name = "Schokolade";
        item.quantity = "5 Tafeln";
        item.id = 17;
        item.status = 0;
        v1.add(item);

        intent.putExtra("ShoppingList", v1);

        startActivity(intent);

ItemListActivity (B):

   public class ItemListActivity extends Activity {
    @Override
    public void onCreate(Bundle savedInstanceState){
        super.onCreate(savedInstanceState);
        setContentView(R.layout.item);
        ListView list = (ListView) findViewById(R.id.ITEMSLIST);
        final Bundle extras = getIntent().getExtras();
        Vector<ItemModel> items = (Vector<ItemModel>) extras.getSerializable("ShoppingList");
        ArrayList<HashMap<String, Object>> itemsList = new ArrayList<HashMap<String, Object>>();
        HashMap<String, Object> itemMap = new HashMap<String, Object>();
}

解决方案

Anything that implements List and Serializable is internally turned into an ArrayList. So it might go in as a Vector but it comes out as an ArrayList. It's probably better to treat it as just a List<> at both ends in the putter and getter.

As a general rule, don't use Vector either. All the methods are synchronized which makes it less efficient than an ArrayList.

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