android中fragment與activity之間通訊原理以及例子

轉自   http://www.jcodecraeer.com/a/anzhuokaifa/androidkaifa/2012/1016/441.html

首先,如果你想在android3.0及以下版本使用fragment,你必須引用android-support-v4.jar這個包

然後你寫的activity不能再繼承自Activity類了,而是要繼承android.support.v4.app.FragmentActivity,一些其他的父類也有相應的變化.

由於在android的實現機制中fragment和activity會被分別執行個體化為兩個不相干的對象,他們之間的聯絡由activity的一個成員對象fragmentmanager來維護.fragment執行個體化後會到activity中的fragmentmanager去註冊一下,這個動作封裝在fragment對象的onAttach中,所以你可以在fragment中聲明一些回調介面,當fragment調用onAttach時,將這些回調介面執行個體化,這樣fragment就能調用各個activity的成員函數了,當然activity必須implements這些介面,否則會包classcasterror

fragment和activity的回調機制又是OOP的一次完美演繹!

下面通過一個例子來說明：

 

我把Activity的UI分為兩個部分，左邊和右邊，左邊用來放置點擊的按鈕(LeftFragment),右邊用來放置對應點擊後顯示的資訊(RightFragment).

Activity的布局layout檔案：main.xml

<?xml version="1.0"encoding="utf-8"?><LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"    android:layout_width="fill_parent"    android:layout_height="fill_parent"    android:orientation="horizontal">        <LinearLayout        android:id="@+id/left_layout"        android:layout_width="wrap_content"        android:layout_height="fill_parent"        android:layout_weight="1"        android:orientation="vertical">     </LinearLayout>       <LinearLayout        android:id="@+id/right_layout"        android:layout_width="wrap_content"        android:layout_height="fill_parent"        android:layout_weight="10"        android:orientation="vertical">     </LinearLayout>   </LinearLayout>

 

LeftFragment的布局layout：leftfragment.xml

<?xml version="1.0"encoding="utf-8"?><LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"    android:layout_width="match_parent"    android:layout_height="match_parent"    android:orientation="vertical">        <Button        android:id="@+id/first_button"        android:layout_width="fill_parent"        android:layout_height="wrap_content"        android:text="@string/first_button"/>        <Button        android:id="@+id/second_button"        android:layout_width="fill_parent"        android:layout_height="wrap_content"        android:text="@string/second_button"/>        <Button        android:id="@+id/third_button"        android:layout_width="fill_parent"        android:layout_height="wrap_content"        android:text="@string/third_button"/>    </LinearLayout>

RightFragment的布局layout:rightfragment.xml

<?xml version="1.0"encoding="utf-8"?><LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"    android:layout_width="match_parent"    android:layout_height="match_parent"    android:orientation="vertical">        <TextView        android:id="@+id/right_show_message"        android:layout_width="fill_parent"        android:layout_height="fill_parent"        android:background="@android:color/holo_orange_dark"        android:textColor="@android:color/white"/>    </LinearLayout>

以上是兩個fragment和一個Activity的布局檔案，下面來看他們的java檔案

Activity:

public class FirstActivity extends Activity implements MyListener {    /**     * 實現MyListener,當LeftFragment中點擊第一頁的時候，讓RightFragment顯示第一頁資訊,同理當點擊第二頁的時候，RightFragment顯示第二頁資訊     *      * @param index      *            顯示的頁數      */    public void showMessage(int index)     {        if(1 == index)             showMessageView.setText(R.string.first_page);        if(2 == index)             showMessageView.setText(R.string.second_page);        if(3 == index)             showMessageView.setText(R.string.third_page);    }       /** 得到RightFragment中顯示資訊的控制項 */    private TextView showMessageView;        /** Called when the activity is first created. */    @Override    public void onCreate(Bundle savedInstanceState)     {        super.onCreate(savedInstanceState);        setContentView(R.layout.main);        System.out.println("Activity--->onCreate");           FragmentManager manager = getFragmentManager();         FragmentTransaction transaction = manager.beginTransaction();         // 動態增加Fragment         RightFragment rightFragment = newRightFragment();         LeftFragment leftFragment = newLeftFragment();         transaction.add(R.id.left_layout, leftFragment, "leftfragment");        transaction.add(R.id.right_layout, rightFragment, "rightfragment");        transaction.commit();       }       @Override    protected void onResume()     {        super.onResume();        System.out.println("Activity--->onResume");        showMessageView = (TextView) findViewById(R.id.right_show_message);     }}

LeftFragment:

public class LeftFragment extends Fragment {    /** Acitivity要實現這個介面，這樣Fragment和Activity就可以共用事件觸發的資源了 */    public interface MyListener     {        public void showMessage(int index);     }       private MyListener myListener;     private Button firstButton;     private Button secondButton;     private Button thirdButton;        /** Fragment第一次附屬於Activity時調用,在onCreate之前調用 */    @Override    public void onAttach(Activity activity)     {        super.onAttach(activity);        System.out.println("LeftFragment--->onAttach");           myListener = (MyListener) activity;     }       @Override    public void onCreate(Bundle savedInstanceState)     {        super.onCreate(savedInstanceState);        System.out.println("LeftFragment--->onCreate");    }       @Override    public View onCreateView(LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState)    {        System.out.println("LeftFragment--->onCreateView");        returninflater.inflate(R.layout.leftfragment, container, false);    }       @Override    public void onResume()     {        super.onResume();        System.out.println("LeftFragment--->onResume");           firstButton = (Button) getActivity().findViewById(R.id.first_button);         secondButton = (Button) getActivity().findViewById(R.id.second_button);         thirdButton = (Button) getActivity().findViewById(R.id.third_button);            MyButtonClickListener clickListener = newMyButtonClickListener();         firstButton.setOnClickListener(clickListener);        secondButton.setOnClickListener(clickListener);        thirdButton.setOnClickListener(clickListener);    }       /** 按鈕的監聽器 */    class MyButtonClickListener implements OnClickListener     {        public void onClick(View v)         {            Button button = (Button) v;             if(button == firstButton)                 myListener.showMessage(1);            if(button == secondButton)                 myListener.showMessage(2);            if(button == thirdButton)                 myListener.showMessage(3);        }    }}

RightFragment:

public class RightFragment extends Fragment {    @Override    public void onCreate(Bundle savedInstanceState)     {        System.out.println("RightFragment--->onCreate");        super.onCreate(savedInstanceState);    }       @Override    public View onCreateView(LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState)    {        System.out.println("RightFragment--->onCreateView");        returninflater.inflate(R.layout.rightfragment, container, false);    }}

注意，Fragment的生命週期和Activity生命週期之間的關係。在Activity裡動態產生Fragment，首先是Activity調用onCreate()方法，但是這時候還沒有載入到Fragment裡的組件，當Fragment調用其onCreateView()方法後，Activity才能得到Fragment中的組件

 

 

 

這裡最關鍵的就是Fragment要有一個介面和這個介面的引用，而這個介面需要Activity去實現它。當Fragment調用onAttach(Activity acitivity)方法的時候，將這個activity傳遞給這個介面引用，這樣，就可以和Activity進行互動了.