Android – communication between tabactivity and embedded activity

I'm trying to find out the best communication practices between the activity and the child activities embedded in this activity

In my activity, there is a button. When I click this button, I want to update the sub activities embedded in this activity. I wrote the following code just to know if it is a good habit. Thank you

Mytabactivity.java

public class Mytabactivity extends tabactivity implements OnClickListener {
    private TabHost m_tabHost;

  public void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.ff_tab_activity);

    LayoutInflater inflater = (LayoutInflater) getSystemService(Context.LAYOUT_INFLATER_SERVICE);

    m_tabHost = getTabHost(); 
    TabHost.TabSpec spec; 
    Intent intent; 

    intent = new Intent().setClass(this, ChildActivity.class);
    spec = m_tabHost.newTabSpec("Tab 1");
    spec.setContent(intent);
    tabView = (TextView) inflater.inflate(R.layout.tab_indicator, null);
    spec.setIndicator(tabView);
    m_tabHost.addTab(spec);

    m_tabHost.setCurrentTab(0);
    ImageView nextButtonIv = (ImageView) findViewById(R.id.next_button);
    nextButtonIv.setOnClickListener(this);
  }

  @Override
  public void onClick(View v) {
    switch (v.getId()) {
    case R.id.next_button:
        synchronized (ChildActivity.class) {
            if (null != ChildActivity.s_childActivity) {
                ChildActivity.s_childActivity.changeUI();
            }
        }
        break;
    }
}

ChildActivity.java

public class ChildActivity extends Activity {
    public static ChildActivity s_childActivity;

    @Override
    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);

        synchronized (MatchupsActivity.class) {
            s_childActivity = this;
        }
        setContentView(R.layout.child_activity);
    }

    public void changeUi() {
        code that changes UI
    }

    protected void onDestroy() {
        super.onDestroy();

        synchronized (MatchupsActivity.class) {
            s_childActivity = null;
        }
}

resolvent:

It looks good. A few notes: – I don't think there's any reason to sync. – I'll change it

ChildActivity.s_childActivity.changeUI();

with

if(ChildActivity.s_childActivity != null){
    ChildActivity.s_childActivity.changeUI();
}

even to the extent that

try{
    ChildActivity.s_childActivity.changeUI();
} catch(Exception e){
    //log
}

Increased paranoid security