Using buttons in Android

Screen change using buttons

Create two activities.

Here I'm using MainActivity(1st Screen) and the FunctionActivity(2nd Screen).

Add a button to the splash activity layout and give a method name to the onClick action.

 <Button  
   android:layout_width="wrap_content"  
   android:layout_height="wrap_content"  
   android:text="Function"  
   android:id="@+id/button3"  
   android:layout_alignParentBottom="true"  
   android:layout_centerHorizontal="true"  
   android:width="150dp"  
   android:onClick="fdemo"/>  
 </Button>  

Then write the following method in the MainActivity

 public void fdemo (View v){  
   Intent i= new Intent(MainActivity.this, Function.class);  
   startActivity(i);  
 }  

Adding About message button(Using toast)

Add a button to the activity layout and give a method name to the onClick action

 <Button  
   android:layout_width="wrap_content"  
   android:layout_height="wrap_content"  
   android:text="About"  
   android:id="@+id/button"  
   android:onClick="about"  
   android:background="#e2dddd"  
   android:width="150dp"  
   android:layout_alignParentTop="true"  
   android:layout_alignLeft="@+id/button2"  
   android:layout_alignStart="@+id/button2"  
   android:layout_marginTop="171dp" />  
 <Button  

Then on the Activity write the following code inside the parent class

 public void about(View v){  
   Toast.makeText(this, "about",  
       Toast.LENGTH_LONG).show();  
 }  

Adding Exit button with a prompt message

Add a button to the activity layout and set the onClick action to "exit".

 <Button  
     android:layout_width="wrap_content"  
     android:layout_height="wrap_content"  
     android:text="exit"  
     android:id="@+id/button2"  
     android:onClick="exit"  
     android:layout_marginTop="77dp"  
     android:width="150dp"  
     android:background="#e2dddd"  
     android:layout_below="@+id/button"  
     android:layout_centerHorizontal="true" />  
 </Button>  




Then write the following code on the activity

 public void exit(View v){  
     AlertDialog.Builder builder = new AlertDialog.Builder(this);  
     builder.setMessage("Are you sure you want to exit?")  
         .setCancelable(false)  
         .setPositiveButton("Yes", new DialogInterface.OnClickListener() {  
           public void onClick(DialogInterface dialog, int id) {  
             Intent intent = new Intent(Intent.ACTION_MAIN);  
             intent.addCategory(Intent.CATEGORY_HOME);  
             intent.setFlags(Intent.FLAG_ACTIVITY_NEW_TASK);  
             startActivity(intent);  
           }  
         })  
         .setNegativeButton("No", new DialogInterface.OnClickListener() {  
           public void onClick(DialogInterface dialog, int id) {  
             dialog.cancel();  
           }  
         });  
     AlertDialog alert = builder.create();  
     alert.show();  
   }  

You can reduce the size of the above code by replacing "null" for the below part.

  new DialogInterface.OnClickListener() {   
       public void onClick(DialogInterface dialog, int id) {   
        dialog.cancel();   
       }   
      }  

Then the code will be as follows.

  public void exit(View v){   
    AlertDialog.Builder builder = new AlertDialog.Builder(this);   
    builder.setMessage("Are you sure you want to exit?")   
      .setCancelable(false)   
      .setPositiveButton("Yes", new DialogInterface.OnClickListener() {   
       public void onClick(DialogInterface dialog, int id) {   
        Intent intent = new Intent(Intent.ACTION_MAIN);   
        intent.addCategory(Intent.CATEGORY_HOME);   
        intent.setFlags(Intent.FLAG_ACTIVITY_NEW_TASK);   
        startActivity(intent);   
       }   
      })   
      .setNegativeButton("No", null);   
    AlertDialog alert = builder.create();   
    alert.show();   
   }   

Adding Exit button without a prompt message

Add a button to the activity layout and set the onClick action to "exit".

  <Button   
    android:layout_width="wrap_content"   
    android:layout_height="wrap_content"   
    android:text="exit"   
    android:id="@+id/button2"   
    android:onClick="exit"   
    android:layout_marginTop="77dp"   
    android:width="150dp"   
    android:background="#e2dddd"   
    android:layout_below="@+id/button"   
    android:layout_centerHorizontal="true" />   
  </Button>   

Then write the following code on the activity

 public void exit(DialogInterface dialog, int id) {  
   Intent intent = new Intent(Intent.ACTION_MAIN);  
   intent.addCategory(Intent.CATEGORY_HOME);  
   intent.setFlags(Intent.FLAG_ACTIVITY_NEW_TASK);  
   startActivity(intent);  
  }