呼叫活动的方法从碎片 [英] Call Activity Method From Fragment

问题描述

我处理片段。
我有一个活动和不同的片段。
每个片段需要访问类（称之为X），允许它访问数据库，但由于我有很多碎片，我不希望创建一个不同的实例类X 中，因为我认为这将需要大量的内存。
所以，我该怎么办？
我写了这样的事情（有一个getter），但它不工作！

I'm dealing with fragments.
I have an Activity and different fragments.
Each fragment need the access to a Class(call it X) that allow it to access a database, but, because I have a lot of fragments, I don't want to create a different instance of the Class X in every fragment as I think it will require lots of memory.
So how can I do?
I wrote something like this (with a getter), but it doesn't work!

public class MyActivity {
  private ClassX classx;

  .....

  public ClassX getClassX() {
     return classx;
  }   
  .....
}

但不是，我怎么能在片段称之为？

推荐答案

这是一点点的Java的问题和Android。

This is a little bit more of a Java question and android.

如果你在看访问数据库，查看创建数据库单。

If you looking at accessing the database, look at creating a database singleton.

所以是这样的：

public class Database {

    // This starts off null
    private static Database mInstance;

    /**
     * Singleton method, will return the same object each time.
     */
    public static final Database getInstance() {
        // First time this method is called by Database.getInstance() from anywhere
        // in your App. It will create this Object once.
        if(mInstance == null) mInstance = new Database();
        // Returns the created object from a statically assigned field so its never
        // destroyed until you do it manually.
        return mInstance;
    }

    //Private constructor to stop you from creating this object by accident
    private Database(){
      //Init db object
    }

}

于是从碎片和活动，你就可以把你们班的以下字段（更好地利用使用基本活动和碎片，以节省您重复code）。

So then from your fragments and activities you can then place the following field in your class's (Better use use a base activity and fragment to save you repeating code).

public abstract class BaseFragment extends Fragment {

    protected final Database mDatabase = Database.getInstance();

}

那么你的混凝土碎片可以延长你的 BaseFragment 如： SearchListFragment延伸BaseFragment

希望这有助于。

值得一读有关单身并的数据库

问候， 克里斯

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