Fragment for Android development

1. Life cycle

• OnAttach () : Called when Fragment is associated with Activity. You can get Activity references through this method, and you can get parameters through getArguments().
• OnCreate () : called when the Fragment is created
• OnActivityCreated () : called when the Activity completes onCreate()
• OnStart () : called when the Fragment is visible.
• OnResume () : called when the Fragment is visible and interactive
• OnPause () : called when the Fragment is visible but not interactive.
• OnStop () : called when Fragment is not visible.
• OnDestroyView () : Called when the Fragment’s UI is removed from the view structure.
• OnDestroy () : called when the Fragment is destroyed.
• OnDetach () : called when the Fragment and Activity are unassociated.

2. Use

2.1 Static Loading

1. Define the Fragment layout and create left_fragment. XML and right_fragment. XML files

      
<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/button"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_gravity="center_horizontal"
        android:text="Button" />
</LinearLayout>
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<LinearLayout
    xmlns:android="http://schemas.android.com/apk/res/android"
    android:orientation="vertical"
    android:background="#00ff00"
    android:layout_width="match_parent"
    android:layout_height="match_parent">

    <TextView
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_gravity="center_horizontal"
        android:textSize="20sp"
        android:text="this is Fragment" />

</LinearLayout>
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2. Create a custom Fragment class that inherits the Fragment or its subclass and overwrites onCreateView(), calling the inflater.inflate() method in the method to load the Fragment layout file and then returning the loaded view object

public class LeftFragment extends Fragment {

    @Override
    public View onCreateView(LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState) {
        View view = inflater.inflate(R.layout.left_fragment, container,false);
        returnview; }}Copy the code

public class RigthFragment extends Fragment {

    @Nullable
    @Override
    public View onCreateView(@NonNull LayoutInflater inflater, @Nullable ViewGroup container, @Nullable Bundle savedInstanceState) {
        View view = inflater.inflate(R.layout.right_fragment, container, false);
        returnview; }}Copy the code

3. Add the Fragment tag to the layout file corresponding to the Activity that needs to load the Fragment

<fragment
    android:id="@+id/left_fragment"
    android:name="com.test.LeftFragment"
    android:layout_width="0dp"
    android:layout_height="match_parent"
    android:layout_weight="1" />
<fragment
    android:id="@+id/right_fragment"
    android:name="com.test.RigthFragment"
    android:layout_width="0dp"
    android:layout_height="match_parent"
    android:layout_weight="1"
    />
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4. Call setContentView() in the Activity’s onCreate() method to load the layout file

Note: Static loads once added cannot be removed at run time

2.2 Dynamic Loading

Chestnut:

1. As with static loading, you define the Fragment’s layout and class first, modify the main layout file, and do not specify the tag’s name attribute.
2. Implementing Fragment calls

public class MainActivity extends AppCompatActivity implements View.OnClickListener {

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        Button button = (Button) findViewById(R.id.button);
        button.setOnClickListener(this);
        replaceFragment(new RigthFragment());
    }

    @Override
    public void onClick(View v) {
        switch (v.getId()) {
            case R.id.button:
                replaceFragment(new AnotherRightFragment());
                break;
            default:
                break; }}private void replaceFragment(Fragment fragment) { FragmentManager fragmentManager = getSupportFragmentManager(); FragmentTransaction transaction = fragmentManager.beginTransaction(); transaction.replace(R.id.right_layout, fragment); transaction.commit(); }}Copy the code

3. Fragment Communicates with the Activity

3.1 An Activity sends data to a Fragment (using the Bundle mode)

chestnuts

1. The layout file for the Activity

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

    <TextView
        android:id="@+id/text"
        android:layout_gravity="center"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:textSize="20dp"
        android:text="I am the Activity" />

    <FrameLayout
        android:layout_below="@+id/button"
        android:id="@+id/fragment_container"
        android:layout_width="match_parent"
        android:layout_height="500dp"/>
</LinearLayout>
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2. Set the Fragment layout file

<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:orientation="vertical"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:background="@color/colorAccent"
    >

    <TextView
        android:id="@+id/fragment"
        android:text="I am fragments"
        android:layout_gravity="center"
        android:textSize="30dp"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        />

    <TextView
        android:id="@+id/text"
        android:layout_gravity="center"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:textSize="20dp"
        android:text="Wait for the Activity to send a message" />

    <Button
        android:id="@+id/button"
        android:layout_gravity="center"
        android:text="Click to receive Activity message"
        android:layout_centerInParent="true"
        android:textSize="20dp"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content" />
</LinearLayout>
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3. Set the Activity’s class file

public class Activity2Fragment extends AppCompatActivity {

    TextView text;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activcity_2_fragment);
        text = (TextView) findViewById(R.id.text);

        // Step 1: Obtain the FragmentManager
        FragmentManager fragmentManager = getFragmentManager();

        // Step 2: Obtain FragmentTransaction
        FragmentTransaction fragmentTransaction = fragmentManager.beginTransaction();

        // Step 3: Create the Fragment to be added
        final mFragment fragment = new mFragment();

        // Step 4: Create the Bundle object
        // Stores data and passes it to the Fragment
        Bundle bundle = new Bundle();

        // Step 5: Add data to the bundle
        bundle.putString("message"."I love Google");

        // Step 6: Set the data to the Fragment
        fragment.setArguments(bundle);

        // Step 7: Dynamically add fragments
        // Add the fragment to the placeholder defined in the Activity layout file (FrameLayout)fragmentTransaction.add(R.id.fragment_container, fragment); fragmentTransaction.commit(); }}Copy the code

4. Set the Fragment class file

public class mFragment extends Fragment {
    Button button;
    TextView text;
    Bundle bundle;
    String message;

    @Override
    public View onCreateView(LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState) {
        View contentView = inflater.inflate(R.layout.fragment, container, false);
        // Set the layout file

        button = (Button) contentView.findViewById(R.id.button);
        text = (TextView) contentView.findViewById(R.id.text);

        // Step 1: Getaranswers () to get all the values passed in from the Activity
        bundle = this.getArguments();

        // Step 2: Get a value
        message = bundle.getString("message");

        // Step 3: Set the button to display the set value
        button.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {

                // Display the value passedtext.setText(message); }});returncontentView; }}Copy the code

3.2 Fragment passing data to an Activity(interface callback)

1. The layout file for the Activity

<RelativeLayout 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"
    android:paddingBottom="@dimen/activity_vertical_margin"
    android:paddingLeft="@dimen/activity_horizontal_margin"
    android:paddingRight="@dimen/activity_horizontal_margin"
    android:paddingTop="@dimen/activity_vertical_margin"
    tools:context="scut.carson_ho.fragment_2_activity.MainActivity">

    <TextView
        android:id="@+id/text"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:textSize="20dp"
        android:text="Waiting for a Fragment to send a message" />

    <Button
        android:id="@+id/button"
        android:layout_below="@+id/text"
        android:text="Click to receive Fragment message"
        android:layout_centerInParent="true"
        android:textSize="10dp"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content" />

    <FrameLayout
        android:layout_below="@+id/button"
        android:id="@+id/fragment_container"
        android:layout_width="match_parent"
        android:layout_height="500dp"/>

</RelativeLayout>
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2. Set the Fragment layout file

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

    <TextView
        android:id="@+id/fragment"
        android:text="I am fragments"
        android:gravity="center"
        android:textSize="30dp"
        android:layout_width="match_parent"
        android:layout_height="match_parent"
        android:background="@color/colorAccent"/>

</LinearLayout>
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3. Set up the callback interface

public interface ICallBack {
    void get_message_from_Fragment(String string);

}
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4. Set the Fragment class file

public class mFragment extends Fragment {

    @Override
    public View onCreateView(LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState) {
        View contentView = inflater.inflate(R.layout.fragment, container, false);
        // Set the layout file
        return contentView;
    }

    // Set the interface callback method
    public void sendMessage(ICallBack callBack){

        callBack.get_message_from_Fragment("Message: I'm from Fragment"); }}Copy the code

5. Set the Acticvity class file

public class MainActivity extends AppCompatActivity {

    Button button;
    TextView text;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);

        button = (Button)findViewById(R.id.button);
        text = (TextView)findViewById(R.id.text);

        // Step 1: Obtain the FragmentManager
        FragmentManager fragmentManager = getFragmentManager();

        // Step 2: Obtain FragmentTransaction
        FragmentTransaction fragmentTransaction = fragmentManager.beginTransaction();

        // Step 3: Create the Fragment to be added
        final mFragment fragment = new mFragment();

        // Step 4: Dynamically add fragments
        // Add the fragment to the placeholder defined in the Activity layout file (FrameLayout)
        fragmentTransaction.add(R.id.fragment_container, fragment);
        fragmentTransaction.commit();


        button.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {

                // Send a message from the fragment to the Activity via an interface callback
                fragment.sendMessage(new ICallBack() {
                    @Override
                    public void get_message_from_Fragment(String string) { text.setText(string); }}); }}); }}Copy the code