我有一个活动,它是整个应用程序中使用的主要活动,它有许多变量。我有另外两个活动,我希望能够使用来自第一个活动的数据。
现在我知道我可以这样做:
GlobalState gs = (GlobalState) getApplication();
String s = gs.getTestMe();
然而,我想要分享很多变量,其中一些可能相当大,所以我不想像上面那样创建它们的副本。
是否有一种方法可以直接获取和更改变量而不使用get和set方法?我记得在谷歌开发网站上读过一篇文章,说不建议在Android上使用这种性能。
Using the hashmap of weak reference approach, described above, and in http://developer.android.com/guide/faq/framework.html seems problematic to me. How are entire entries reclaimed, not just the map value? What scope do you allocate it in? As the framework is in control of the Activity lifecycle, having one of the participating Activities own it risks runtime errors when the owner is destroyed in advance of its clients. If the Application owns it, some Activity must explicitly remove the entry to avoid the hashmap from holding on to entries with a valid key and a potentially garbaged collected weak reference. Furthermore, what should a client do when the value returned for a key is null?
在我看来,由应用程序拥有或在单例中拥有WeakHashMap是更好的选择。映射中的值是通过键对象访问的,当不存在对键的强引用时(即所有活动都使用键及其映射到的对象完成),GC可以回收映射条目。
如果你的意图是从当前Activity调用其他Activity,你应该使用intent。您可以将重点放在按需共享数据而不是持久化数据上。
However, if you really need to persist these values then you could persist them in some kind of structured text file or database on local storage. A properties file, XML file, or JSON file could store your data and be easily parsed during activity creation. Don't forget also that you have SQLite on all Android devices, so you could store them in a database table. You could also use a Map to store key-value pairs and serialize the map to local storage, but this might be too cumbersome to be useful for simple data structures.
在活动之间共享数据有多种方式
1:使用Intent在活动之间传递数据
Intent intent=new Intent(this, desirableActivity.class);
intent.putExtra("KEY", "Value");
startActivity(intent)
2:使用静态关键字,将变量定义为公共静态,并在项目中使用任何位置
public static int sInitialValue=0;
在项目的任何地方使用classname.variableName;
3:使用数据库
但其过程较长,插入数据时必须使用查询,需要时使用游标迭代数据。但是如果不清理缓存就不会丢失数据。
4:使用共享首选项
比数据库简单多了。但是有一些限制,你不能保存ArrayList,List和自定义对象。
5:在application类中创建getter setter,并访问项目中的任何地方。
private String data;
public String getData() {
return data;
}
public void setData(String data) {
this.data = data;
}
这里设置和获取活动
((YourApplicationClass)getApplicationContext()).setData("abc");
String data=((YourApplicationClass)getApplicationContext()).getData();