How to prevent the activity from loading twice on pressing the button

Add this to your Activity definition in AndroidManifest.xml...

android:launchMode = "singleTop"

For example:

<activity
            android:name=".MainActivity"
            android:theme="@style/AppTheme.NoActionBar"
            android:launchMode = "singleTop"/>

In the button's event listener, disable the button and show another activity.

    Button b = (Button) view;
    b.setEnabled(false);

    Intent i = new Intent(this, AnotherActitivty.class);
    startActivity(i);

Override onResume() to re-enable the button.

@Override
    protected void onResume() {
        super.onResume();

        Button button1 = (Button) findViewById(R.id.button1);
        button1.setEnabled(true);
    }