Parcelable还是Singleton？(Parcelable or Singleton?)

Parcelable还是Singleton？(Parcelable or Singleton?)

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); } });

并检索这种方式：

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。

我有兴趣看看你对此有何看法。 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。 如果你看到任何看起来不对的东西，请告诉我！

I am working on a project that involves me having to share an array list of objects with all of the activities that make up the application. Until recently I was passing the list between activities by implementing the parcelable interface. An example of this is seen below:

MenuItem class:

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); }

}

Order class - which I would change to be the Singleton (holds list of menu items)

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); }

}

This is how I pass the data between activities:

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); } });

and retrieve this way:

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; } }

Today I learned about the use of a Singleton for global access to data, and I am wondering would it be a good idea to switch to this style of data access? It seems easier to control and a lot tidier with respects to the code.

I'd be interested to see what your opinions on this are. This link here is the pattern I would like to implement:

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

I should mention, the project is part of my studies in my course. I have to submit my code in a few weeks time, so I am looking for the best way to make it more efficient. So please let me know if you see anything that looks wrong as well!

最满意答案

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"

...并访问它：

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

There is very little reason to use Parcelable to move an object around inside a single Linux process. I suggest making your menu a static member of a custom Application object, something like this:

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; } .... }

Make sure that the list is immutable, so that you don't have to worry about concurrency issues.

In your manifest:

<application android:name=".MyApplication"

... and access it with:

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