fragment与activity之间通信原理以及例子

来源：互联网发布：重庆程序员招聘信息编辑：程序博客网时间：2024/05/16 02:13

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,否则会报错

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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1. <?xml version="1.0"encoding="utf-8"?>

2. <LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"

3. android:layout_width="fill_parent"

4. android:layout_height="fill_parent"

5. android:orientation="horizontal">

7. <LinearLayout

8. android:id="@+id/left_layout"

9. android:layout_width="wrap_content"

10. android:layout_height="fill_parent"

11. android:layout_weight="1"

12. android:orientation="vertical">

13. </LinearLayout>

14.

15. <LinearLayout

16. android:id="@+id/right_layout"

17. android:layout_width="wrap_content"

18. android:layout_height="fill_parent"

19. android:layout_weight="10"

20. android:orientation="vertical">

21. </LinearLayout>

22.

23. </LinearLayout>

LeftFragment的布局layout：leftfragment.xml

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1. <?xml version="1.0"encoding="utf-8"?>

2. <LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"

3. android:layout_width="match_parent"

4. android:layout_height="match_parent"

5. android:orientation="vertical">

7. <Button

8. android:id="@+id/first_button"

9. android:layout_width="fill_parent"

10. android:layout_height="wrap_content"

11. android:text="@string/first_button"/>

12.

13. <Button

14. android:id="@+id/second_button"

15. android:layout_width="fill_parent"

16. android:layout_height="wrap_content"

17. android:text="@string/second_button"/>

18.

19. <Button

20. android:id="@+id/third_button"

21. android:layout_width="fill_parent"

22. android:layout_height="wrap_content"

23. android:text="@string/third_button"/>

24.

25. </LinearLayout>

RightFragment的布局layout:rightfragment.xml

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1. <?xml version="1.0"encoding="utf-8"?>

2. <LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"

3. android:layout_width="match_parent"

4. android:layout_height="match_parent"

5. android:orientation="vertical">

7. <TextView

8. android:id="@+id/right_show_message"

9. android:layout_width="fill_parent"

10. android:layout_height="fill_parent"

11. android:background="@android:color/holo_orange_dark"

12. android:textColor="@android:color/white"/>

13.

14. </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:

[java] view plaincopy

1. public class FirstActivityextends Activityimplements MyListener

2. {

3. /**

4. *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

5. *

6. * @param index

7. * 显示的页数

8. */

9. public void showMessage(int index)

10. {

11. if(1 == index)

12. showMessageView.setText(R.string.first_page);

13. if(2 == index)

14. showMessageView.setText(R.string.second_page);

15. if(3 == index)

16. showMessageView.setText(R.string.third_page);

17. }

18.

19. /** 得到RightFragment中显示信息的控件 */

20. private TextView showMessageView;

21.

22. /** Called when the activity is first created. */

23. @Override

24. public void onCreate(Bundle savedInstanceState)

25. {

26. super.onCreate(savedInstanceState);

27. setContentView(R.layout.main);

28. System.out.println("Activity--->onCreate");

29.

30. FragmentManager manager = getFragmentManager();

31. FragmentTransaction transaction = manager.beginTransaction();

32. //动态增加Fragment

33. RightFragment rightFragment = newRightFragment();

34. LeftFragment leftFragment = newLeftFragment();

35. transaction.add(R.id.left_layout, leftFragment, "leftfragment");

36. transaction.add(R.id.right_layout, rightFragment,"rightfragment");

37. transaction.commit();

38.

39. }

40.

41. @Override

42. protected void onResume()

43. {

44. super.onResume();

45. System.out.println("Activity--->onResume");

46. showMessageView = (TextView) findViewById(R.id.right_show_message);

47. }

48. }

LeftFragment:

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1. public class LeftFragmentextends Fragment

2. {

3. /** 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 */

4. public interface MyListener

5. {

6. public void showMessage(int index);

7. }

9. private MyListener myListener;

10. private Button firstButton;

11. private Button secondButton;

12. private Button thirdButton;

13.

14. /** Fragment第一次附属于Activity时调用,在onCreate之前调用 */

15. @Override

16. public void onAttach(Activity activity)

17. {

18. super.onAttach(activity);

19. System.out.println("LeftFragment--->onAttach");

20.

21. myListener = (MyListener) activity;

22. }

23.

24. @Override

25. public void onCreate(Bundle savedInstanceState)

26. {

27. super.onCreate(savedInstanceState);

28. System.out.println("LeftFragment--->onCreate");

29. }

30.

31. @Override

32. public View onCreateView(LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState)

33. {

34. System.out.println("LeftFragment--->onCreateView");

35. returninflater.inflate(R.layout.leftfragment, container, false);

36. }

37.

38. @Override

39. public void onResume()

40. {

41. super.onResume();

42. System.out.println("LeftFragment--->onResume");

43.

44. firstButton = (Button) getActivity().findViewById(R.id.first_button);

45. secondButton = (Button) getActivity().findViewById(R.id.second_button);

46. thirdButton = (Button) getActivity().findViewById(R.id.third_button);

47.

48. MyButtonClickListener clickListener = newMyButtonClickListener();

49. firstButton.setOnClickListener(clickListener);

50. secondButton.setOnClickListener(clickListener);

51. thirdButton.setOnClickListener(clickListener);

52. }

53.

54. /**按钮的监听器 */

55. class MyButtonClickListenerimplements OnClickListener

56. {

57. public void onClick(View v)

58. {

59. Button button = (Button) v;

60. if(button == firstButton)

61. myListener.showMessage(1);

62. if(button == secondButton)

63. myListener.showMessage(2);

64. if(button == thirdButton)

65. myListener.showMessage(3);

66. }

67. }

68. }

RightFragment:

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1. public class RightFragmentextends Fragment

2. {

3. @Override

4. public void onCreate(Bundle savedInstanceState)

5. {

6. System.out.println("RightFragment--->onCreate");

7. super.onCreate(savedInstanceState);

8. }

10. @Override

11. public View onCreateView(LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState)

12. {

13. System.out.println("RightFragment--->onCreateView");

14. returninflater.inflate(R.layout.rightfragment, container,false);

15. }

16. }

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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