Question

很抱歉，如果这是一个非常明显的问题。简而言之，我将数组列表从TshirtParadiseActivity传递到ShopActivity。在ShopActivity中，我将数组列表传递给Adapter类，该类创建复选框的侦听器，以便它们在选中时修改数组列表。

我可以在ShopActivity的onDestroy（）方法中看到对原始arraylist所做的更改。但是，一旦该活动消失，即使我先前已在TshirtParadiseActivity中添加了该活动，但我又返回了一个空白列表。

如何在活动之间保留对阵列列表的更改？我在下面包含了我的代码：

TshirtParadiseActivity.java

ShopActivity

ShopActivity.java

package com.bignerdranch.android.tshirtparadise;

import android.content.Intent;
import android.support.v7.app.AppCompatActivity;
import android.os.Bundle;
import android.view.View;
import android.widget.Button;

import java.util.ArrayList;
import java.util.List;

public class TshirtParadiseActivity extends AppCompatActivity {

    private Button mSexy0;
    private Button mCheckOut;
    private int POOR=0;
    private ArrayList<Tshirt> shoppingCart = new ArrayList<Tshirt>();
    private static final int requestCodeShop=0;
    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_tshirt_paradise);
        mSexy0 = (Button) findViewById(R.id.sexy0);
        mCheckOut = (Button) findViewById(R.id.checkout);

        mCheckOut.setOnClickListener(new View.OnClickListener(){
           @Override
           public void onClick(View v){
               //ARRAYLIST IS EMPTY
               for (int i=0;i<shoppingCart.size();i++){
                   System.out.println("you bought a " + shoppingCart.get(i).getTitle() +
                           " for $" + shoppingCart.get(i).getPrice());
               }
           }
        });

        mSexy0.setOnClickListener(new View.OnClickListener(){
            @Override
            public void onClick(View v){
                Intent i = ShopActivity.newIntent(TshirtParadiseActivity.this,0,shoppingCart);
                startActivity(i);
            }
        });
    }    
}

TshirtAdapter.java

public class ShopActivity extends AppCompatActivity {

    private RecyclerView shirtRecyclerView;
//    private ShirtAdapter shirtAdapter;
    private int mQuality;
    TshirtAdapter teeAdapter;
    private List<Tshirt> teeShirtList;
    private static ArrayList<Tshirt>shoppingCart;
    private static final String QUALITY = "com.bignerdranch.android.tshirtparadise.muchquality";
    private static String CART = "com.bignerdranch.android.tshirtparadise.cart";
    private static final String BUY = "com.bignerdranch.android.tshirtparadise.buy";

    public static Intent newIntent(Context context, int quality,ArrayList<Tshirt>shoppingCart){
        //creates an instance of ShopActivity class
        Intent i = new Intent(context,ShopActivity.class);
        i.putExtra(QUALITY,quality);
        i.putExtra(CART,(Serializable)shoppingCart);
        return i;
    }

    @Override
    protected void onCreate(Bundle savedInstanceState){
        super.onCreate(savedInstanceState);
        //Activities are presented to the user
        setContentView(R.layout.activity_shop);
        TShirtCabinet cabinet = new TShirtCabinet();
        Bundle bundle = getIntent().getExtras();
        mQuality = bundle.getInt(QUALITY);
        //to transform serializable to arraylist, use getSerializable(String name)
        shoppingCart = (ArrayList<Tshirt>) bundle.getSerializable(CART);

        teeShirtList = cabinet.getList(mQuality);
        shirtRecyclerView = (RecyclerView)findViewById(R.id.tshirt_list);
        shirtRecyclerView.setLayoutManager(new LinearLayoutManager(ShopActivity.this));
        teeAdapter = new TshirtAdapter(teeShirtList,shoppingCart);
        shirtRecyclerView.setAdapter(teeAdapter);
    }
}

}

Answer 1

将对象放入Intent并将其发送到另一个Activity时，大多数情况下，您都会在对象中获得该对象的不同实例。新的Activity。列表中可能包含所有相同的值，但是就程序而言，它是一个不同的列表。

如果要查看在第二项活动中所做的更改反映在第一个活动中，则应使用活动“结果”。在第一个活动中，通过调用startActivityForResult()而不是startActivity()来启动第二个活动。在第二个活动中，在致电setResult()之前先致电finish()。然后，回到第一个活动，通过实现onActivityResult()处理该结果，并在那里更新列表。

有意通过了ArrayList但未进行任何更改？

1 个答案: