Android Fragment uses full parsing

The use of Fragment is a commonplace~~~

1. Overview

Since the introduction of Fragment in API 11, Fragment has become popular. Now most projects use Fragment to some extent. It is lighter, more suitable for screens, and more convenient for UI design. What is Fragment after all this talk?

Fragment: A fragment is an application's user interface and behavior that can be placed on an activity. At its core, it represents a specific operation or interface that runs on a larger activity. It represents an interface because it can be used as a View in a layout, and it represents a specific operation because it contains a life cycle for logical operations. In short, a fragment is a component with a life cycle. (Please correct me if you have any questions!)

Features of Fragment:

• The life cycle must depend on the Activity. When the Activity is destroyed, all fragments will be destroyed. (I have stepped into this pit myself)
• Lightweight, lightweight switching.
• It is convenient to handle the interface differences between tablets and phones.

2. Inheritance structure and life cycle

Inheritance structure:

Fragment directly inherits Object and has four direct subclasses. I personally rarely use its subclasses.

life cycle:

The life cycle of Fragment is clearly marked in the figure, so I won't repeat it. This figure was collected a long time ago, and I have forgotten the original source. Thanks to the original author!

3. Basic use

1). Static use

Static use means that Fragment is used in the layout like a control.

TestFragment.java inherits Fragment and rewrites the onCreateView method

 /**
 * Created by magic on September 27, 2016.
 */
 public class TestFragment extends Fragment { 
 
 @Override
 public   View onCreateView(LayoutInflater inflater, ViewGroup container,
            Bundle savedInstanceState) {
 View   view = inflater.inflate(R.layout.fragment_main, container);
        ImageView img=(ImageView) view .findViewById(R.id.img);
        img.setOnClickListener(new View .OnClickListener() {
 @Override
 public void onClick( View v) {
 Toast.makeText(getActivity(), "This is a fragment" , Toast.LENGTH_SHORT).show();
 }
 });
 return   view ;
 } 
 
 }

fragment_main.xml

 <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" > 
 
 <ImageView
        android:id= "@+id/img"  
        android:layout_width= "wrap_content"  
        android:layout_height= "wrap_content"  
        android:layout_centerInParent= "true"  
        android:src= "@drawable/img" /> 
 
 </RelativeLayout>

MainActivity.java actually does nothing.

 /**
 * Created by magic on September 27, 2016.
 */
 public class MainActivity extends Activity { 
 
 @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
 } 
 
 }

activity_main.xml

 <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" > 
 
 <fragment
        android:id= "@+id/id_fragment"  
        android:layout_width= "match_parent"  
        android:layout_height= "match_parent"  
        class= "com.magic.test_fragment.TestFragment" /> 
 
 </RelativeLayout>

Use the fragment tag to add a fragment and specify the full class name of the fragment through class.

Operation effect:

[[177766]]

2) Dynamic use

Dynamic use means dynamically adding, replacing, removing, hiding, and displaying fragments in the fragment layout container.

CommonFragment.java

 /**
 * Created by magic on September 27, 2016. General Fragment
 */
 @SuppressLint( "ValidFragment" )
 public class CommonFragment extends Fragment { 
 
 String desc ; 
 
 public CommonFragment(String desc ) {
 super();
 this.desc = desc ;
 } 
 
 @Override
 public   View onCreateView(LayoutInflater inflater, ViewGroup container,
            Bundle savedInstanceState) {
 View   view = inflater.inflate(R.layout.fragment_common, container, false );
        TextView tev = (TextView) view .findViewById(R.id.tev);
        System.out .println ( desc );
 tev.setText( desc );
 return   view ;
 } 
 
 }

Set the content on the TextView by passing data through the constructor.

fragment_common.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/tev"  
        android:layout_width= "match_parent"  
        android:layout_height= "match_parent"  
        android:gravity= "center"  
        android:textColor= "@color/mainOrange" /> 
 
 </LinearLayout>

MainActivity.java

 /**
 * Created by magic on September 27, 2016. Bottom tab + fragment
 */
 public class MainActivity extends Activity implements OnClickListener { 
 
    TextView tev_tab1, tev_tab2, tev_tab3, tev_tab4; 
 
 // fragment transaction class
 FragmentTransaction ft;
 // fragment
    CommonFragment tabFragment1, tabFragment2, tabFragment3, tabFragment4; 
 
    @SuppressLint( "CommitTransaction" )
 @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main2);
 initView(); 
 
        ft = getFragmentManager().beginTransaction(); 
 
        tabFragment1 = new CommonFragment( "Tab1" );
 // Replace
        ft. replace (R.id.container, tabFragment1);
        // submit
 ft.commit ();
 } 
 
 // Initialize the control
 private void initView() {
        tev_tab1 = (TextView) findViewById(R.id.tev_tab1);
        tev_tab2 = (TextView) findViewById(R.id.tev_tab2);
        tev_tab3 = (TextView) findViewById(R.id.tev_tab3);
        tev_tab4 = (TextView) findViewById(R.id.tev_tab4); 
 
        tev_tab1.setOnClickListener(this);
        tev_tab2.setOnClickListener(this);
        tev_tab3.setOnClickListener(this);
        tev_tab4.setOnClickListener(this);
 } 
 
 @Override
 public void onClick( View v) { 
 
        FragmentTransaction ft = getFragmentManager().beginTransaction(); 
 
 switch (v.getId()) {
 case R.id.tev_tab1:
            ft. replace (R.id.container, tabFragment1);
 break;
 case R.id.tev_tab2:
            if (tabFragment2 == null ) {
                tabFragment2 = new CommonFragment( "Tab2" );
 }
            ft. replace (R.id.container, tabFragment2);
 break;
 case R.id.tev_tab3:
            if (tabFragment3 == null ) {
                tabFragment3 = new CommonFragment( "Tab3" );
 }
            ft. replace (R.id.container, tabFragment3);
 break;
 case R.id.tev_tab4:
            if (tabFragment4 == null ) {
                tabFragment4 = new CommonFragment( "Tab4" );
 }
            ft. replace (R.id.container, tabFragment4);
 break;
 }
        // submit
 ft.commit ();
 } 
 
 }

activity_main2.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" > 
 
 <FrameLayout
        android:id= "@+id/container"  
        android:layout_width= "match_parent"  
        android:layout_height= "0dp"  
        android:layout_weight= "1" /> 
 
 <LinearLayout
        android:layout_width= "match_parent"  
        android:layout_height= "50dp"  
        android:background= "@color/mainTextBlack"  
        android:orientation= "horizontal" > 
 
 <TextView
            android:id= "@+id/tev_tab1"  
            android:layout_width= "0dp"  
            android:layout_height= "match_parent"  
            android:layout_weight= "1"  
            android:gravity= "center"  
            android:text= "Tab1"  
            android:textColor= "@color/white" /> 
 
 <TextView
            android:id= "@+id/tev_tab2"  
            android:layout_width= "0dp"  
            android:layout_height= "match_parent"  
            android:layout_weight= "1"  
            android:gravity= "center"  
            android:text= "Tab2"  
            android:textColor= "@color/white" /> 
 
 <TextView
            android:id= "@+id/tev_tab3"  
            android:layout_width= "0dp"  
            android:layout_height= "match_parent"  
            android:layout_weight= "1"  
            android:gravity= "center"  
            android:text= "Tab3"  
            android:textColor= "@color/white" /> 
 
 <TextView
            android:id= "@+id/tev_tab4"  
            android:layout_width= "0dp"  
            android:layout_height= "match_parent"  
            android:layout_weight= "1"  
            android:gravity= "center"  
            android:text= "Tab4"  
            android:textColor= "@color/white" />
 </LinearLayout> 
 
 </LinearLayout>

Create a Fragment container through the FrameLayout tag, and add listener events to the four tabs at the bottom to dynamically replace the Fragment in the FrameLayout container.

Operation effect:

4. Related classes and main methods

FragmentManager fragment manager, an abstract class, is implemented in the FragmentManagerImpl class in Android-support-v4.jar.

 // Get the FragmentManager object
 FragmentManager manager = getFragmentManager();

FragmentTransaction is an abstract class, which is implemented in the BackStackRecord class. The final implementation of operations such as adding, deleting, and replacing is still in the FragmentManagerImpl class.

 // Get the FragmentTransaction object
        FragmentTransaction transaction = manager.beginTransaction(); 
 
 // Add fragment
 transaction.add ( ) ;
 transaction .add (containerViewId, fragment, tag) ;
 // Replace the existing fragment that will be added to the container
 transaction.replace ( ) ;
 // Delete an existing fragment
 transaction .remove(); 
 
 // Save the current fragment data to avoid view redrawing
 transaction .hide();
 // Show the previously hidden fragment
 transaction .show();
 // These two methods will trigger the onHiddenChanged(boolean hidden) callback in the fragment 
 
 // Display the previous data The instance will not be destroyed, but the view hierarchy will still be destroyed, that is, onDestoryView and onCreateView will be called
 transaction .addToBackStack( null );
 //Transaction commit
 transaction . commit ();

Fragment Fragment Class

 Fragment fragment = new Fragment(); 
 
 // Return the Activity currently associated with this fragment
        fragment.getActivity();
 //Set data
        fragment.setArguments(new Bundle());
 // Get data
        fragment.getArguments();
 // Returns the FragmentManager that acts on this fragment
        fragment.getFragmentManager();
 // Get the tag name
 fragment.getTag(); 
 
 //Callback when the hidden state changes
        // onHiddenChanged( true );

If you are interested, you can go to Read The Fucking Source. Anyway, I find it quite confusing...

5. Others

To be continued…