Question

我正在开发一个涉及我必须与构成应用程序的所有活动共享对象的数组列表的项目。直到最近，我才通过实现parcelable接口在活动之间传递列表。下面是一个例子：

MenuItem类：

ublic class MenuItem implements Parcelable {

private String name;
private double price;
private int qty;
private String info;

public MenuItem(String name, double price) {
    super();
    this.name = name;
    this.price = price;
}
public MenuItem() {
    // TODO Auto-generated constructor stub
}
public String getName() {
    return name;
}
public void setName(String name) {
    this.name = name;
}
public double getPrice() {
    return price;
}
public void setPrice(double price) {
    this.price = price;
}

public int getQty() {
    return qty;
}
public void setQty(int qty) {
    this.qty = qty;
}
public String getInfo() {
    return info;
}
public void setInfo(String info) {
    this.info = info;
}
@Override
public String toString() {
    return name;
}


//Parcelable methods.
public static final Parcelable.Creator<MenuItem> CREATOR = new Parcelable.Creator<MenuItem>() {

    @Override
    public MenuItem createFromParcel(Parcel source) {
        return new MenuItem(source);
    }

    @Override
    public MenuItem[] newArray(int size) {
        return new MenuItem[size];
    }
};

public MenuItem(Parcel source) {
    this();
    readFromParcel(source);
}

private void readFromParcel(Parcel source) {
    name = source.readString();
    price = source.readDouble();
}

@Override
public int describeContents() {
    return 0;
}

@Override
public void writeToParcel(Parcel dest, int flags) {
    dest.writeString(name);
    dest.writeDouble(price);
}

}

订单类 - 我将更改为Singleton（保存菜单项列表）

public class Order implements Parcelable {


private int covers;
private int table;
private ArrayList<MenuItem> items;


public Order(){
    super();
    this.items = new ArrayList<MenuItem>();

}

public static final Parcelable.Creator<Order> CREATOR = new Parcelable.Creator<Order>() {

    @Override
    public Order createFromParcel(Parcel source) {
        return new Order(source);
    }

    @Override
    public Order[] newArray(int size) {
        return new Order[size];
    }


};

public Order(int covers, int table) {
    super();
    this.covers = covers;
    this.table = table;
    this.items = new ArrayList<MenuItem>();
}

public int getCovers() {
    return covers;
}

public void setCovers(int covers) {
    this.covers = covers;
}

public int getTable() {
    return table;
}

public void setTable(int table) {
    this.table = table;
}

public ArrayList<MenuItem> getItems() {
    return items;
}

public void setItems(ArrayList<MenuItem> items) {
    this.items = items;
}

//add to order
public void addToOrder(MenuItem m){
    items.add(m);
}

//remove from order
public void removeFromOrder(MenuItem m){
    items.remove(m);
}

public Order(Parcel source) {
    this();
    readFromParcel(source);
}

@Override
public int describeContents() {
    // TODO Auto-generated method stub
    return 0;
}

@Override
public void writeToParcel(Parcel dest, int flags) {
    // TODO Auto-generated method stub
    dest.writeInt(covers);
    dest.writeInt(table);
    dest.writeTypedList(items);

}

private  void readFromParcel(Parcel source) {
    // TODO Auto-generated method stub
    covers = source.readInt();
    table = source.readInt();
    items = new ArrayList<MenuItem>();
    source.readTypedList(items,  MenuItem.CREATOR);

}

}

这是我在活动之间传递数据的方式：

myOrderBtn.setOnClickListener(new View.OnClickListener() {

        @Override
        public void onClick(View v) {
            Toast.makeText(v.getContext(), "myOrderBtn", Toast.LENGTH_SHORT).show();
            Intent i = new Intent(v.getContext(), ViewOrderActivity.class);
            i.putExtra("data", order);
            if(!saved){
            saveOrderState();
            }
            startActivity(i);

        }
    });

并以这种方式检索：

public void getOrderData(){
    Intent i = getIntent();
    if(i != null && i.hasExtra("data")){
        order = i.getParcelableExtra("data");
        Toast.makeText(this.getApplicationContext(), "STARTERS recieved order object, covers: " + order.getCovers() + " table no: " + order.getTable() + " order size: " + order.getItems().size(), Toast.LENGTH_SHORT).show();

        if(order.getItems().size() == 0){
            //Toast.makeText(this.getApplicationContext(), "No items added to your order...", Toast.LENGTH_SHORT).show();
        }else{
            for(int j = 0; j != order.getItems().size(); j++){
                dishItems.add(order.getItems().get(j));
            }
        }

        saved = false;

    }
}

今天我学会了使用Singleton进行全局数据访问，我想知道切换到这种数据访问方式是个好主意吗？对代码的尊重似乎更容易控制和更整洁。

我很想知道你对此有何看法。这里的链接是我想要实现的模式：

http://www.devahead.com/blog/2011/06/extending-the-android-application-class-and-dealing-with-singleton/

我应该提一下，这个项目是我课程学习的一部分。我必须在几周内提交我的代码，所以我正在寻找提高效率的最佳方法。如果您发现任何看起来不对的内容，请告诉我们！

Answer 1

没有理由使用Parcelable在单个Linux进程内移动对象。我建议你的菜单是自定义Application对象的静态成员，如下所示：

public class MyApplication extends Application {
    private static final List<MenuItem> menu;
    static {
        List<MenuItem> l = new ArrayList<MenuItems>();
        l.add(new MenuItem(...));
        ...
        menu = Collections.unmodifiableList(l);
    }

    ...

    public List<MenuItems> getMenu() { return menu; }

    ....

}

确保列表是不可变的，这样您就不必担心并发问题。

在你的清单中：

<application
    android:name=".MyApplication"

...并使用以下方式访问它：

List<MenuItem> menu = ((MyApplication) getApplication()).getMenu();

Parcelable还是Singleton？

1 个答案: