Detailed explanation of Fragment usage

Learn with you for lifeXi, this is Programmer Android

Recommended classic articles. By reading this article, you will gain the following knowledge points:

1. Introduction to Fragment
2. Design principles of Fragment
3. Fragment life cycle
4. How to use Fragment in Activity
5. Method to dynamically add Fragment to Activity
6. Get Fragment in Activity
7. How to get Fragment to host Activity
8. Two Methods for communicating with a Fragment
9. Methods for communicating between Fragment and Activity
10. References

1. Introduction to Fragment

Before learning Fragment, we need to understand the inheritance relationship of Fragment. The inheritance relationship of Fragment is as follows:

java.lang.Object
   ↳ android.app.Fragment

Fragment Fragments, Activity often used in responsible for user interface parts, can be Fragmentcombined into one Activityto create multiple windows UI, or Activityreused in a fragment Fragment. You can Fragment think of it as Activitya modular component that Fragmenthas its own life cycle, can receive its own input events, and can be Activityadded or removed at runtime Fragment.

FragmentMust be nested in Activity, and its life cycle is Activityaffected by the life cycle.

2. Design principles of Fragment

FragmentMainly to provide support for more dynamic and flexible UIdesigns on large screens (tablets, etc.). Since tablet screens are much larger than phone screens, there's UI more space available for combining and swapping components. When Fragmentimplementing this type of design, you don't need to manage complex changes to the view hierarchy. By  Activitybreaking the layout into parts Fragment, you can modify the appearance at runtime Activity and  Activity persist those changes in a managed back stack.

You should Fragmentdesign each one as a reusable modular Activity component. That is, since each Fragment defines its own layout and behavior through its own lifecycle callbacks, you can add one to Fragmentmultiple Activity, so you should adopt a reusable design and avoid directly Fragmentmanipulating one from another a Fragment. This is especially important because modular fragments allow you to Fragmentadapt to different screen sizes by changing the way they are combined. When designing an app that works on both tablets and phones, you can reuse yours in different layout configurations Fragmentto optimize the user experience based on available screen space. For example, on a mobile phone, if  Activitymultiple clips cannot be stored in the same one, you may have to use separate clips to achieve a single pane UI.

Combine two Fragments into one Activity to adapt to tablets, and use one Fragment to adapt to mobile phones

3. Fragment life cycle

1. Fragment life cycle diagram

Fragment life cycle diagram

2.  FragmentLife cycle callback method

public void onAttach(Context context) {
        // TODO Auto-generated method stub
        Log.i(TAG, "----onAttach----");
        super.onAttach(context);
    }

    @Override
    public void onCreate(Bundle savedInstanceState) {
        Log.i(TAG, "----onCreate----");
        // 在Fragment 中调用Activity 中的方法
        ((FragmentAutoCreate) getActivity()).test();

        // TODO Auto-generated method stub
        super.onCreate(savedInstanceState);
    }

    @Override
    public View onCreateView(LayoutInflater inflater, ViewGroup container,
            Bundle savedInstanceState) {
        Log.i(TAG, "----onCreateView----");
        // 将layout布局转换成View
        View view = inflater.inflate(R.layout.fragment_left_layout, null);
        Toast.makeText(getActivity(),
                "通过对外提供方法setMsg(String msg)，供Activity 调用", 0).show();
        return view;

    }

    @Override
    public void onActivityCreated(Bundle savedInstanceState) {
        Log.i(TAG, "----onActivityCreated----");
        // TODO Auto-generated method stub
        super.onActivityCreated(savedInstanceState);
    }

    @Override
    public void onStart() {
        Log.i(TAG, "----onStart----");
        // TODO Auto-generated method stub
        super.onStart();
    }

    @Override
    public void onResume() {
        Log.i(TAG, "----onResume----");
        // TODO Auto-generated method stub
        super.onResume();
    }

    @Override
    public void onPause() {
        Log.i(TAG, "----onPause----");
        // TODO Auto-generated method stub
        super.onPause();
    }

    @Override
    public void onStop() {
        Log.i(TAG, "----onStop----");
        // TODO Auto-generated method stub
        super.onStop();
    }

    @Override
    public void onDestroyView() {
        Log.i(TAG, "----onDestroyView----");
        // TODO Auto-generated method stub
        super.onDestroyView();
    }

    @Override
    public void onDestroy() {
        Log.i(TAG, "----onDestroy----");
        // TODO Auto-generated method stub
        super.onDestroy();
    }

    @Override
    public void onDetach() {
        Log.i(TAG, "----onDetach----");
        // TODO Auto-generated method stub
        super.onDetach();
    }

3.Fragment in the life cycle of the host Activity

FragmentIt cannot Activityexist without separation, and its life cycle is Activity affected by the life cycle.

Activity and Fragment life cycle interaction diagram

Log print information is as above

4. How to use Fragment in Activity

1. Staticly add Fragment to Activity

<fragment
        android:id="@+id/left_fragment"
        android:layout_width="0dp"
        android:layout_height="match_parent"
        android:layout_weight="1"
        class="com.programandroid.Fragment.FragmentLeft" />

2. Create a custom Fragment class

The implementation method is as follows

public class FragmentRight extends Fragment {
    @Override
    public View onCreateView(LayoutInflater inflater, ViewGroup container,
            Bundle savedInstanceState) {
        // 将layout布局转换成View
        View view = inflater.inflate(R.layout.fragment_right_layout, null);

        // 取出值
        Bundle values = getArguments();
        if (values != null) {
            String str = values.getString("key", "");
            Toast.makeText(getActivity(), "接收Activity传递的至为：" + str, 0).show();

        } else {
            Toast.makeText(getActivity(), "接收Activity传递的至为空", 0).show();

        }

        return view;

    }
}

5. Dynamically add Fragment to Activity

1. Create a custom Fragment class

public class FragmentRight extends Fragment {
    @Override
    public View onCreateView(LayoutInflater inflater, ViewGroup container,
            Bundle savedInstanceState) {
        // 将layout布局转换成View
        View view = inflater.inflate(R.layout.fragment_right_layout, null);

        // 取出值
        Bundle values = getArguments();
        if (values != null) {
            String str = values.getString("key", "");
            Toast.makeText(getActivity(), "接收Activity传递的至为：" + str, 0).show();

        } else {
            Toast.makeText(getActivity(), "接收Activity传递的至为空", 0).show();

        }

        return view;

    }
}

2. Create a Fragment to fill the layout vector

<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:tools="http://schemas.android.com/tools"
    android:layout_width="match_parent"
    android:layout_height="match_parent" >

    <FrameLayout
        android:id="@+id/fl_left"
        android:layout_width="0dp"
        android:layout_height="match_parent"
        android:layout_weight="1"
        android:background="#f00" />

    <FrameLayout
        android:id="@+id/fl_right"
        android:layout_width="0dp"
        android:layout_height="match_parent"
        android:layout_weight="2"
        android:background="#0f0" />

</LinearLayout>

3. Use FragmentManager to dynamically populate

1. Create the container that the container Fragment receives Activity.
2. Use FragmentManagerand Fragmentinteract with
3. Open the transaction and  the created container will Fragment be filled. 4. Submit the transaction.Activity

public class FragmentAutoCreate extends Activity {
    @Override
    protected void onCreate(Bundle savedInstanceState) {
        // TODO Auto-generated method stub
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_fragment_autocreate);

        // 获取fragmentManager --->开启事务--->容器中填充内容--->提交事务
        // FragmentManager : Activity 内部用来与Fragment进行交互的接口
        FragmentManager fragmentManager = getFragmentManager();
        // 开启一个事务
        FragmentTransaction transaction = fragmentManager.beginTransaction();
        // 将左右两侧的Fragment 添加的R.id.fl_left 所代表的容器视图中
        FragmentLeft leftFragment = new FragmentLeft();
        transaction.add(R.id.fl_left, leftFragment, "left_tag");
        // 1. 调用 Fragment 对外提供的方法
        leftFragment.setMsg("tttt");

        FragmentRight rightFragment = new FragmentRight();
        // 2. Activity --setArguments-> 创值给Fragment
        Bundle args = new Bundle();
        args.putString("key", "Activity --setArguments-> 创值给Fragment ");
        // 传递数据
        rightFragment.setArguments(args);
        transaction.add(R.id.fl_right, rightFragment);
        // transaction.replace(R.id.fl_right, rightFragment);
        // transaction.hide(rightFragment);
        transaction.show(rightFragment);

        // 提交事务
        transaction.commit();

    }

    public void test() {

    }
}

6. Obtain Fragment from Activity

Fragment idFragment=getFragmentManager().findFragmentById(R.id.fl_left);
        FragmentRight tagFragment = (FragmentRight) getFragmentManager().findFragmentByTag("left_tag");

7. Fragment’s method of obtaining the host Activity

1.  getActivity()Method to obtain宿主Activity

public View onCreateView(LayoutInflater inflater, ViewGroup container,
            Bundle savedInstanceState) {
        Log.i(TAG, "----onCreateView----");
        // 将layout布局转换成View
        View view = inflater.inflate(R.layout.fragment_left_layout, null);
        Toast.makeText(getActivity(),
                "通过对外提供方法setMsg(String msg)，供Activity 调用", 0).show();
        return view;

    }

8. Communication method between two Fragments

 1. Obtain different values ​​​​through the host Activity to methodFragmentMangerFragment

Fragment idFragment=getFragmentManager().findFragmentById(R.id.fl_left);
        FragmentRight tagFragment = (FragmentRight) getFragmentManager().findFragmentByTag("left_tag");

9. Communication method between Fragment and Activity

1.Activity calls the setArguments method

public class FragmentAutoCreate extends Activity {
    @Override
    protected void onCreate(Bundle savedInstanceState) {
        // TODO Auto-generated method stub
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_fragment_autocreate);

        // 获取fragmentManager --->开启事务--->容器中填充内容--->提交事务
        // FragmentManager : Activity 内部用来与Fragment进行交互的接口
        FragmentManager fragmentManager = getFragmentManager();
        // 开启一个事务
        FragmentTransaction transaction = fragmentManager.beginTransaction();
        // 将左右两侧的Fragment 添加的R.id.fl_left 所代表的容器视图中
        FragmentLeft leftFragment = new FragmentLeft();
        transaction.add(R.id.fl_left, leftFragment, "left_tag");
        // 1. 调用 Fragment 对外提供的方法
        leftFragment.setMsg("tttt");

        FragmentRight rightFragment = new FragmentRight();
        // 2. Activity --setArguments-> 创值给Fragment
        Bundle args = new Bundle();
        args.putString("key", "Activity --setArguments-> 创值给Fragment ");
        // 传递数据
        rightFragment.setArguments(args);
        transaction.add(R.id.fl_right, rightFragment);
        // transaction.replace(R.id.fl_right, rightFragment);
        // transaction.hide(rightFragment);
        transaction.show(rightFragment);
        // 提交事务
        transaction.commit();
    }

    public void test() {
    }
}

2. Provide interface methods to the outside world through Fragment

By Fragmentproviding external interface methods for Activitycalling

public class FragmentLeft extends Fragment {

    private static final String TAG = "   F   wj";
    private String mMessage;

    public void setMsg(String msg) {
        this.mMessage = msg;
    }


    @Override
    public void onCreate(Bundle savedInstanceState) {
        Log.i(TAG, "----onCreate----");
        // 在Fragment 中调用Activity 中的方法
        ((FragmentAutoCreate) getActivity()).test();

        // TODO Auto-generated method stub
        super.onCreate(savedInstanceState);
    }

    @Override
    public View onCreateView(LayoutInflater inflater, ViewGroup container,
            Bundle savedInstanceState) {
        Log.i(TAG, "----onCreateView----");
        // 将layout布局转换成View
        View view = inflater.inflate(R.layout.fragment_left_layout, null);
        Toast.makeText(getActivity(),
                "通过对外提供方法setMsg(String msg)，供Activity 调用", 0).show();
        return view;

    }

references:

[Tencent Documentation] Android basic knowledge base
https://docs.qq.com/doc/DSWdKRWh1VnVHYWFP

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