Fragments Basic Knowledge

-

Fragment Lifecycle :

The Correlation between Activity and Fragment Lifecycle considering Fragment is created on creation of Activity

OnCreate - A

onAttach - F

onCreate - F

onCreateView - F

onActivityCreated - F

onStart - F

onStart - A

onResume - A

onResume - F

onPause - F

onPause - A

onStop - F

onStop - A

onDestroyView - F

onDestroy - F

onDetach - F

onDestroy - A


The Correlation between Activity and Fragment Lifecycle considering Activity is created 1st and then the fragment is added

OnCreate - A

onStart - A

onResume - A

onAttach - F

onCreate - F

onCreateView - F

onActivityCreated - F

onStart - F

onResume - F

onPause - F

onPause - A

onStop - F

onStop - A

onDestroyView - F

onDestroy - F

onDetach - F

onDestroy - A


The Correlation between Activity and Fragment Lifecycle considering Activity is created 1st and then the fragment is added to back stack and back pressed

OnCreate - A

onStart - A

onResume - A

onAttach - F

onCreate - F

onCreateView - F

onActivityCreated - F

onStart - F

onResume - F

onPause - F

onStop - F

onDestroyView - F

onDestroy - F

onDetach - F

onPause - A

onStop - A

onDestroy - A

Steps for Adding a fragment :

  1. Create a layout for fragment
  2. Create a fragment class and extend with Fragment class
  3. Set the layout file to the defined fragment
  4. Add a layout that will host the fragment
  5. Write code to add Fragment to Activity in Activity
Fragments should not be aware of each other
Fragments should not launch other fragments
Activity should be aware of all fragments
Actovity should perform Add/Remove/Replace actions

We can Add, Remove and Replace a fragment. This can be done using Fragment Transaction. To get hold of Fragment Transaction, We will be using a API called Fragment Manager.

1. Fragment Manager - Use method from  Activity to get Fragment Manager
2. Fragment Transaction - Provides 3 API's to Add, Replace or Remove the fragment. beginTransaction() will get the Fragment Transaction
We need to invoke Fragment Transaction on Fragment Manager Instance

Add Transaction : 
MainActivity.Java

public class MainActivity extends AppCompatActivity {

    Button add;

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

        add = findViewById(R.id.btnAdd);

        add.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View view) {
                addFragment();
            }
        });
    }

    private void addFragment() {
        Fragment sampleFragment = new SampleFragment();
        FragmentManager fragmentManager = getSupportFragmentManager();
        FragmentTransaction fragmentTransaction = fragmentManager.beginTransaction();
        fragmentTransaction.add(R.id.fragmentContainer, sampleFragment, "demofragment");
        // This statement will remove the fragment from the activity when we press back button
        // Doesn't affect activity lifecycle
        fragmentTransaction.addToBackStack("fragmentStack1");
        fragmentTransaction.commit();
    }
}
Activity back stack is managed by ActivityManager managed by Android Platform itself
Fragment back stack is managed by FragmentManager and needs to be managed by Developer

activity_main.xml
<?xml version="1.0" encoding="utf-8"?>
<androidx.constraintlayout.widget.ConstraintLayout
    xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:app="http://schemas.android.com/apk/res-auto"
    xmlns:tools="http://schemas.android.com/tools"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:background="@color/pale_blue_200"
    tools:context=".MainActivity">

    <FrameLayout
        android:layout_width="match_parent"
        android:layout_height="match_parent"
        android:id="@+id/fragmentContainer"
        android:layout_margin="5dp" />

</androidx.constraintlayout.widget.ConstraintLayout>

SampleFragment.Java
public class SampleFragment extends Fragment {

    @Nullable
    @Override
    public View onCreateView(@NonNull LayoutInflater inflater, @Nullable ViewGroup container,
                         @Nullable Bundle savedInstanceState) {
        return inflater.inflate(R.layout.fragment_sample, container, false);
    }
}
fragment_sample.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"
    android:background="@color/pale_green_200">

</LinearLayout>
Playing with Back Stack : 
Adding Fragment and Removing them from Back Stack
MainActivity.xml
public class MainActivity extends AppCompatActivity {

    private final String TAG = this.getClass().getSimpleName();
    Button add;
    TextView txtFragCount;
    FragmentTransaction fragmentTransaction;
    FragmentManager fragmentManager;

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

        add = findViewById(R.id.btnAdd);
        txtFragCount = (TextView)findViewById(R.id.txtFragCount);
        fragmentManager = getSupportFragmentManager();

        txtFragCount.setText("Frag Count in BackStack " + fragmentManager.getBackStackEntryCount());

        add.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View view) {
                addFragment();
            }
        });

        fragmentManager.addOnBackStackChangedListener(new FragmentManager.OnBackStackChangedListener() {
            @Override
            public void onBackStackChanged() {
                txtFragCount.setText("Frag Count in BackStack " + fragmentManager.getBackStackEntryCount());
            }
        });

        Log.i(TAG, "Initial BackStackCount : "+fragmentManager.getBackStackEntryCount());
    }

    private void addFragment() {
        Fragment fragment;
        switch(fragmentManager.getBackStackEntryCount()) {
            case 0 : fragment = new SampleFragment();
                    break;
            case 1 : fragment = new FragmentTwo();
                    break;
            case 2 : fragment = new FragmentThree();
                    break;
            default : fragment = new SampleFragment();
                break;
        }

        fragmentTransaction = fragmentManager.beginTransaction();
        fragmentTransaction.add(R.id.fragmentContainer, fragment, "demofragment");
        // This statement will remove the fragment from the activity when we press back button
        // Doesn't affect activity lifecycle
        fragmentTransaction.addToBackStack(null);
        fragmentTransaction.commit();
    }
}
activity_main.xml
<?xml version="1.0" encoding="utf-8"?>
<androidx.constraintlayout.widget.ConstraintLayout
    xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:app="http://schemas.android.com/apk/res-auto"
    xmlns:tools="http://schemas.android.com/tools"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:background="@color/pale_blue_200"
    tools:context=".MainActivity">

    <Button
        android:id="@+id/btnAdd"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text="Add Fragment"
        app:layout_constraintBottom_toBottomOf="parent"
        app:layout_constraintEnd_toEndOf="parent"
        app:layout_constraintHorizontal_bias="0.498"
        app:layout_constraintStart_toStartOf="parent"
        app:layout_constraintTop_toTopOf="parent"
        app:layout_constraintVertical_bias="0.023" />

    <TextView
        android:id="@+id/txtFragCount"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        app:layout_constraintBottom_toBottomOf="parent"
        app:layout_constraintEnd_toEndOf="parent"
        app:layout_constraintHorizontal_bias="0.498"
        app:layout_constraintStart_toStartOf="parent"
        app:layout_constraintTop_toBottomOf="@+id/btnAdd"
        app:layout_constraintVertical_bias="0.041" />

    <FrameLayout
        app:layout_constraintTop_toBottomOf="@+id/txtFragCount"
        android:id="@+id/fragmentContainer"
        android:layout_width="match_parent"
        android:layout_height="match_parent"
        android:layout_margin="5dp"
        android:layout_marginTop="428dp"
        app:layout_constraintTop_toTopOf="parent"
        tools:layout_editor_absoluteX="16dp">

    </FrameLayout>

</androidx.constraintlayout.widget.ConstraintLayout>
fragment_sample/two/three.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"
    android:gravity="center"
    android:background="@color/pale_green_200">

    <TextView
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:gravity="center"
        android:textSize="100sp"
        android:text="1" />

</LinearLayout>

Playing with Fragments without Back Stack :
Add, Remove and Replace Fragments
public class MainActivity extends AppCompatActivity {

    private final String TAG = this.getClass().getSimpleName();
    Button add;
    TextView txtFragCount;
    FragmentTransaction fragmentTransaction;
    FragmentManager fragmentManager;

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

        add = findViewById(R.id.btnAdd);
        txtFragCount = (TextView)findViewById(R.id.txtFragCount);
        fragmentManager = getSupportFragmentManager();

        txtFragCount.setText("Frag Count in BackStack " + fragmentManager.getBackStackEntryCount());

        add.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View view) {
                addFragment();
            }
        });

        fragmentManager.addOnBackStackChangedListener(new FragmentManager.OnBackStackChangedListener() {
            @Override
            public void onBackStackChanged() {
                txtFragCount.setText("Frag Count in BackStack " + fragmentManager.getBackStackEntryCount());
            }
        });

        Log.i(TAG, "Initial BackStackCount : "+fragmentManager.getBackStackEntryCount());
    }

    private void addFragment() {
        Fragment fragment = fragmentManager.findFragmentById(R.id.fragmentContainer);
        if(fragment instanceof SampleFragment) {
            fragment = new FragmentTwo();
        } else if(fragment instanceof FragmentTwo) {
            fragment = new FragmentThree();
        } else if(fragment instanceof FragmentThree) {
            fragment = new SampleFragment();
        } else {
            fragment = new SampleFragment();
        }

        fragmentTransaction = fragmentManager.beginTransaction();
        fragmentTransaction.replace(R.id.fragmentContainer, fragment, "demofragment");
        // This statement will remove the fragment from the activity when we press back button
        // Doesn't affect activity lifecycle
        fragmentTransaction.addToBackStack(null);
        fragmentTransaction.commit();
    }

    @Override
    public void onBackPressed() {
        Fragment fragment = fragmentManager.findFragmentById(R.id.fragmentContainer);
        if(fragment != null) {
            fragmentTransaction = fragmentManager.beginTransaction();
            fragmentTransaction.remove(fragment);
            fragmentTransaction.commit();
        } else {
            super.onBackPressed();
        }
    }
}
fragmentTransaction.replace(R.id.fragmentContainer, fragment, "demofragment");
fragmentTransaction.add(R.id.fragmentContainer, fragment, "demofragment");
Add : Will add the fragments one over other and will pop in LIFO when back pressed.
Replace : Will replace the existing fragment with the new fragment. 
Only 1 fragment instance remains at any instance of time

Pop Back Stack are of three types :
Assuming we have 4 fragments added sequentially to backstack with positions mentioned as 
shown below
eg : 
FragFour - 3
FragThree - 2
FragTwo - 1
FragOne - 0
  1. fm.popBackStack() - The default backstack which pops individual fragments from the backstack
  2. fm.popBackStack(int id, int flags) - The 1st int variable refers to the position/id of the 
fragments to be removed. 
Eg: Suppose we pass (1,0) then Frag at position 2 and 3 are popped out and position 1 
i.e FragTwo will be at the top of backstack
Suppose we pass (1,POP_BACK_STACK_INCLUSIVE) then Frag at position 1, 2 and 3 are popped out 
and position 1 i.e FragOne will be at the top of backstack
  3. fm.popBackStack(String name, int flags) - the String name refers to the string that we has
used to add to the Back Stack ie fragmentTransaction.addToBackStack("Add "+fragment.toString())
Eg: Suppose we pass fm.popBackStack("Add FragTwo", 0) then Frag at position 2 and 3 are popped 
out and position 1 i.e FragTwo will be at the top of backstack

Special Cases : Suppose we have the following situation
FragTwo - 5
FragTwo - 4
FragFour - 3
FragThree - 2
FragTwo - 1
FragOne - 0
Suppose we pass fm.popBackStack("Add FragTwo", POP_BACK_STACK_INCLUSIVE), now 5 and 4 will be removed
    & if we call fm.popBackStack("Add FragTwo", POP_BACK_STACK_INCLUSIVE) again then 3, 2, 1 will be removed

MainActivity.xml
public class MainActivity extends AppCompatActivity implements View.OnClickListener{

    private static final String COMMON_TAG = "CombinedLifeCycle";
    private static final String ACTIVITY_NAME = MainActivity.class.getSimpleName();
    private static final String TAG = ACTIVITY_NAME;

    FragmentManager fragmentManager;
    FragmentTransaction fragmentTransaction;

    private Button buttonAddFragmentOne, buttonpopFragment, buttonRemoveFragment;
    private TextView textViewFragmentCount;

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

        buttonAddFragmentOne = (Button)findViewById(R.id.buttonAddFragmentOne);
        buttonpopFragment = (Button)findViewById(R.id.buttonPopFragment);
        buttonRemoveFragment = (Button)findViewById(R.id.buttonRemoveFragment);
        textViewFragmentCount = (TextView)findViewById(R.id.textViewFragmentCount);

        fragmentManager=getSupportFragmentManager();

        textViewFragmentCount.setText("Fragment count in back stack: "+fragmentManager.getBackStackEntryCount());

        fragmentManager.addOnBackStackChangedListener(new FragmentManager.OnBackStackChangedListener() {
            @Override
            public void onBackStackChanged() {
                textViewFragmentCount.setText("Fragment count in back stack: "+fragmentManager.getBackStackEntryCount());

                StringBuilder stringBuilder=new StringBuilder("Current status of transaction back stack: "+fragmentManager.getBackStackEntryCount()+"\n");
                for(int i=(fragmentManager.getBackStackEntryCount()-1); i>=0;i--){
                    FragmentManager.BackStackEntry backStackEntry =  fragmentManager.getBackStackEntryAt(i);
                    stringBuilder.append(backStackEntry.getName()+"\n");
                }
                Log.i(TAG,stringBuilder.toString());
            }
        });

        Log.i(COMMON_TAG,"Initial BackStackEntryCount: "+fragmentManager.getBackStackEntryCount());

        buttonAddFragmentOne.setOnClickListener(this);
        buttonpopFragment.setOnClickListener(this);
        buttonRemoveFragment.setOnClickListener(this);
    }

    private void addFragment(){
        Fragment fragment;
        if(fragmentManager.getBackStackEntryCount()>0){
            switch (fragmentManager.getBackStackEntryCount()){
                case 0: loadFragmentOne(); break;
                case 1: loadFragmentTwo();break;
                case 2: loadFragmentThree(); break;
                default: loadFragmentOne(); break;
            }
        }else {
            fragment = fragmentManager.findFragmentById(R.id.fragmentContainer);
            if(fragment instanceof SampleFragment){
                loadFragmentTwo();
            }else if(fragment instanceof FragmentTwo){
                loadFragmentThree();
            }else if(fragment instanceof FragmentThree){
                loadFragmentOne();
            }else{
                loadFragmentOne();
            }
        }
    }

    private void loadFragmentOne(){
        Fragment fragment;
        fragmentTransaction = fragmentManager.beginTransaction();
        fragment = fragmentManager.findFragmentByTag("demofragment");
        /*if(fragment!=null){
            fragmentTransaction.remove(fragment);
        }*/
        fragment = new SampleFragment();
        fragmentTransaction.replace(R.id.fragmentContainer,fragment,"demofragment");
        fragmentTransaction.addToBackStack("Add "+fragment.toString());
        fragmentTransaction.commit();
    }

    private void loadFragmentTwo(){

        Fragment fragment;
        fragmentTransaction = fragmentManager.beginTransaction();
        fragment = fragmentManager.findFragmentByTag("demofragment");
        /*if(fragment!=null){
            fragmentTransaction.remove(fragment);
        }*/
        fragment = new FragmentTwo();
        fragmentTransaction.replace(R.id.fragmentContainer,fragment,"demofragment");
        fragmentTransaction.addToBackStack("Add "+fragment.toString());
        fragmentTransaction.commit();
    }

    private void loadFragmentThree(){
        Fragment fragment;
        fragmentTransaction = fragmentManager.beginTransaction();
        fragment = fragmentManager.findFragmentByTag("demofragment");
        /*if(fragment!=null){
            fragmentTransaction.remove(fragment);
        }*/
        fragment = new FragmentThree();
        fragmentTransaction.replace(R.id.fragmentContainer,fragment,"demofragment");
        fragmentTransaction.addToBackStack("Add "+fragment.toString());
        fragmentTransaction.commit();
    }

    @Override
    public void onClick(View view) {
        switch (view.getId()){
            case R.id.buttonAddFragmentOne: addFragment(); break;
            case R.id.buttonPopFragment: fragmentManager.popBackStack("Add SampleFragment",FragmentManager.POP_BACK_STACK_INCLUSIVE); break;
            case R.id.buttonRemoveFragment:
                fragmentTransaction = fragmentManager.beginTransaction();
                Fragment fragment=fragmentManager.findFragmentById(R.id.fragmentContainer);
                if(fragment!=null){
                    fragmentTransaction.remove(fragment);
                    fragmentTransaction.addToBackStack("Remove "+fragment.toString());
                    fragmentTransaction.commit();
                }else{
                    Toast.makeText(this,"No Fragment to remove",Toast.LENGTH_SHORT).show();
                }
                break;
            default: break;
        }
    }
}
activity_main.xml
<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:app="http://schemas.android.com/apk/res-auto"
    xmlns:tools="http://schemas.android.com/tools"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:orientation="vertical"
    android:background="@color/pale_blue_200"
    tools:context=".MainActivity">

    <LinearLayout
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:orientation="horizontal"
        android:weightSum="3">

        <Button
            android:id="@+id/buttonAddFragmentOne"
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:layout_weight="1"
            android:text="Add" />

        <Button
            android:id="@+id/buttonPopFragment"
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:layout_weight="1"
            android:text="Pop" />

        <Button
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:id="@+id/buttonRemoveFragment"
            android:text="Remove"
            android:layout_weight="1"/>

    </LinearLayout>

    <TextView
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:textSize="20sp"
        android:textColor="@color/pale_green_200"
        android:id="@+id/textViewFragmentCount"
        android:gravity="center"/>

    <FrameLayout
        android:layout_width="match_parent"
        android:layout_height="match_parent"
        android:id="@+id/fragmentContainer"
        android:layout_margin="5dp" />

</LinearLayout>

Comments

Post a Comment

Popular posts from this blog

Android - Using KeyStore to encrypt and decrypt the data

-
import android.content.Context; import android.os.Build; import android.security.keystore.KeyGenParameterSpec; import android.security.keystore.KeyProperties; import android.support.annotation. RequiresApi ; import android.util.Base64; import java.io.UnsupportedEncodingException; import java.security.InvalidAlgorithmParameterException; import java.security.InvalidKeyException; import java.security.KeyStore; import java.security.KeyStoreException; import java.security.NoSuchAlgorithmException; import java.security.NoSuchProviderException; import java.security.UnrecoverableKeyException; import javax.crypto.BadPaddingException; import javax.crypto.Cipher; import javax.crypto.IllegalBlockSizeException; import javax.crypto.KeyGenerator; import javax.crypto.NoSuchPaddingException; import javax.crypto.SecretKey; import javax.crypto.spec.GCMParameterSpec; public class KeyStoreUtil { private static final String FIXED_IV = "467096543987" ; KeyStore keyStore ; Contex...
Read more

Stack and Queue

-
Image
  What is Stack? Stack is a linear data structure that follows the specific order to perform the operations. For example, if we want to access the element in the array we can do it any time but in the case of stack data structure, there is only one sequence to access the element. In the stack, we insert the element from one end with push operation and delete the element from the same end using pop operation. The end of the stack used to perform all the operations is called the top of the stack. Therefore, a stack follows the LIFO (Last In First Out) principle, which means the element that is inserted last will be the first element to come out of the stack. The most important thing to remember in the stack data structure is that it stores the elements of the same data type only.     Let us understand the condition to check whether the stack is empty for full: Condition to Check if Stack is Empty int Empty() { if (top ==- 1 ) return 1 ; else return 0 ; }   Con...
Read more

Java Reflection API

-
Java Reflection  is a process of examining or modifying the run time behavior of a class at run time The  java.lang.Class  class provides many methods that can be used to get metadata, examine and change the run time behavior of a class. The java.lang and java.lang.reflect packages provide classes for java reflection The java.lang.Class class performs mainly two tasks: provides methods to get the metadata of a class at run time. provides methods to examine and change the run time behavior of a class. How to get the object of Class class? There are 3 ways to get the instance of Class class. They are as follows: forName() method of Class class getClass() method of Object class the .class syntax 1) forName() method of Class class is used to load the class dynamically. returns the instance of Class class. It should be used if you know the fully qualified name of class.This cannot be used for primitive types. Let's see the simple example of forName() meth...
Read more