android中fragment与activity之间通信原理以及例子

首先,如果你想在android3.0及以下版本使用fragment,你必须引用android-support-v4.jar这个包

然后你写的activity不能再继承自Activity类了,而是要继承android.support.v4.app.FragmentActivity,一些其他的父类也有相应的变化.

由于在android的实现机制中fragment和activity会被分别实例化为两个不相干的对象,他们之间的联系由activity的一个成员对象fragmentmanager来维护.fragment实例化后会到activity中的fragmentmanager去注册一下,这个动作封装在fragment对象的onAttach中,所以你可以在fragment中声明一些回调接口,当fragment调用onAttach时,将这些回调接口实例化,这样fragment就能调用各个activity的成员函数了,当然activity必须implements这些接口,否则会包classcasterror

fragment和activity的回调机制又是OOP的一次完美演绎!

下面通过一个例子来说明：

我把Activity的UI分为两个部分，左边和右边，左边用来放置点击的按钮(LeftFragment),右边用来放置对应点击后显示的信息(RightFragment).

Activity的布局layout文件：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>

以上是两个fragment和一个Activity的布局文件，下面来看他们的java文件

Activity:

public class FirstActivity extends Activity implements MyListener
{
    /**
     * 实现MyListener,当LeftFragment中点击第一页的时候，让RightFragment显示第一页信息,同理当点击第二页的时候，RightFragment显示第二页信息
     *
     * @param index
     *            显示的页数
     */
    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中显示信息的控件 */
    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();
        // 动态增加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要实现这个接口，这样Fragment和Activity就可以共享事件触发的资源了 */
    public interface MyListener
    {
        public void showMessage(int index);
    }

    private MyListener myListener;
    private Button firstButton;
    private Button secondButton;
    private Button thirdButton;

    /** Fragment第一次附属于Activity时调用,在onCreate之前调用 */
    @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);
    }

    /** 按钮的监听器 */
    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的生命周期和Activity生命周期之间的关系。在Activity里动态生成Fragment，首先是Activity调用onCreate()方法，但是这时候还没有加载到Fragment里的组件，当Fragment调用其onCreateView()方法后，Activity才能得到Fragment中的组件

 http://blog.csdn.net/guozh/article/details/25327685

这里最关键的就是Fragment要有一个接口和这个接口的引用，而这个接口需要Activity去实现它。当Fragment调用onAttach(Activity acitivity)方法的时候，将这个activity传递给这个接口引用，这样，就可以和Activity进行交互了.