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android中fragment与activity之间通信原理以及例子

2014-11-04 10:31 691 查看

摘要首先,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frag

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

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<?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

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<?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

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<?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:

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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 =

new

RightFragment();

LeftFragment leftFragment =

new

LeftFragment();

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:

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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"

);

return

inflater.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 =

new

MyButtonClickListener();

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:

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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"

);

return

inflater.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

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.

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