I can't replace my default fragment(home fragment) to other fragments using button click event?
<p>i'm new to Android and struggling with my fragments project, pls help me out!
here i cant replace my default fragment(containing three buttons) to other fragments using button click event. 
ps: => problem : my code works fine and compiles too, but button is not responding
here's my code</p>

<p>activity_main.xml </p>

<pre><code>   &lt;LinearLayout
        android:layout_width="match_parent"
        android:layout_height="match_parent"
        android:orientation="vertical"&gt;

    &lt;FrameLayout
        android:layout_width="match_parent"
        android:layout_height="match_parent"
        android:id="@+id/main_container"
        /&gt;


   &lt;Button
        android:layout_width="150dp"
        android:layout_height="wrap_content"
        android:text="ABOUT ME"
        android:id="@+id/bttn_about"
        android:layout_gravity="center_horizontal" /&gt;

    &lt;Button
        android:layout_width="150dp"
        android:layout_height="wrap_content"
        android:text="MY SKILLS"
        android:id="@+id/bttn_skills"
        android:layout_gravity="center_horizontal" /&gt;

    &lt;Button
        android:layout_width="150dp"
        android:layout_height="wrap_content"
        android:text="CONTACT ME"
        android:layout_below="@+id/bttn_skills"
        android:layout_gravity="center_horizontal" /&gt;
&lt;/LinearLayout&gt;
</code></pre>

<p>and here's my java file.</p>

<p>mainActivity.java</p>

<p>public class MainActivity extends AppCompatActivity {</p>

<pre><code>  Button bttn_about,bttn_skills,bttn_contact;
  FragmentTransaction fragmentTransaction;

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

    fragmentTransaction = getSupportFragmentManager().beginTransaction();
    fragmentTransaction.add(R.id.main_container,new HomeFragment());
    fragmentTransaction.commit();

    bttn_about=(Button)findViewById(R.id.bttn_about);
    bttn_skills=(Button)findViewById(R.id.bttn_skills);
    bttn_contact=(Button)findViewById(R.id.bttn_contact);

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

   //FragmentManager,Fragment Transaction..... same as above code
       }
    });

  }
</code></pre>

<p>and here's the second fragment </p>

<pre><code> &lt;FrameLayout 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"
  tools:context="com.example.AboutmeFragment"&gt;

&lt;!-- TODO: Update blank fragment layout --&gt;
 &lt;RelativeLayout
   android:layout_width="match_parent"
   android:layout_height="wrap_content"&gt;
  &lt;TextView
    android:layout_width="wrap_content"
    android:layout_height="wrap_content"
    android:layout_marginTop="80dp"
    android:textAppearance="?android:attr/textAppearanceLarge"
    android:text="@string/aboutme"
    android:id="@+id/textView2"
    android:layout_gravity="left|top" /&gt;
   &lt;/RelativeLayout&gt;
  &lt;/FrameLayout&gt;
</code></pre>