some code about fragment

//MainActivity.java
//-------------------------------------
package cn.micoder.myfragmenttest;

import android.support.v7.app.ActionBarActivity;
import android.os.Bundle;
import android.view.Menu;
import android.view.MenuItem;

public class MainActivity extends ActionBarActivity implements bottomfragment.getText {

@Override
public void gettext(String s) {
topfragment topFragment = (topfragment)getSupportFragmentManager().findFragmentById(R.id.fragment);
topFragment.settext(s);
}

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

}

@Override
public boolean onCreateOptionsMenu(Menu menu) {
// Inflate the menu; this adds items to the action bar if it is present.
getMenuInflater().inflate(R.menu.menu_main, menu);
return true;
}

@Override
public boolean onOptionsItemSelected(MenuItem item) {
// Handle action bar item clicks here. The action bar will
// automatically handle clicks on the Home/Up button, so long
// as you specify a parent activity in AndroidManifest.xml.
int id = item.getItemId();

//noinspection SimplifiableIfStatement
if (id == R.id.action_settings) {
return true;
}

return super.onOptionsItemSelected(item);
}

public void change(){

}

}
//-----------------------------------------
//topfragment.java
//-------------------------------
package cn.micoder.myfragmenttest;

//创建FRAGMENT须导入
import android.os.Bundle;
import android.support.v4.app.Fragment;
import android.view.LayoutInflater;
import android.view.View;
import android.view.ViewGroup;
import android.widget.TextView;

public class topfragment extends Fragment {

TextView toptext;

//棋覆写onCreaeView方法
@Override
public View onCreateView(LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState) {
View view = inflater.inflate(R.layout.topfragment,container,false);//将XML文件布局实例化
toptext = (TextView)view.findViewById(R.id.toptext);
return view;
}

protected void settext(String s){
toptext.setText(s);
}
}
//-------------------------
//bottomfragment.java
//----------------------------
package cn.micoder.myfragmenttest;

import android.app.Activity;
import android.os.Bundle;
import android.support.v4.app.Fragment;
import android.view.LayoutInflater;
import android.view.ViewGroup;
import android.view.View;

import android.widget.EditText;
import android.widget.Button;

public class bottomfragment extends Fragment {

EditText edittext;
Button mybutton;
getText getBottomText;//定义getText类型变量

//创建接口
public interface getText{
public void gettext(String s);
}

//FRAGMENT被加载到ACTIVITY时执行
@Override
public void onAttach(Activity activity) {
super.onAttach(activity);//调用父类的onAttach方法
try{
getBottomText = (getText)activity;//获得ACTIVITY实例，强转换成接口类型
}catch (ClassCastException e){
throw new ClassCastException(activity.toString());//如果ACTIVITY没有实现这个接口则抛出异常
}
}

@Override
public View onCreateView(LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState) {
View view = inflater.inflate(R.layout.bottomfragment,container,false);
mybutton = (Button)view.findViewById(R.id.mybutton);
edittext = (EditText)view.findViewById(R.id.myedittext);
mybutton.setOnClickListener(
new View.OnClickListener() {
@Override
public void onClick(View v) {
change();
}
}
);
return view;
}

public void change(){
getBottomText.gettext(edittext.getText().toString());
}
}