在MainActivity的内部静态类PlaceholderFragment 类中的onCreateView中获取fragment_main.xml中控件

package com.example.edittext;

import android.app.Activity;
import android.app.Fragment;
import android.os.Bundle;
import android.view.LayoutInflater;
import android.view.Menu;
import android.view.MenuItem;
import android.view.View;
import android.view.View.OnClickListener;
import android.view.ViewGroup;
import android.widget.Button;
import android.widget.EditText;
import android.widget.Toast;

public class MainActivity extends Activity {

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

if (savedInstanceState == null) {
getFragmentManager().beginTransaction()
.add(R.id.container, new PlaceholderFragment()).commit();
}

}

@Override
public boolean onCreateOptionsMenu(Menu menu) {

// Inflate the menu; this adds items to the action bar if it is present.
getMenuInflater().inflate(R.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();
if (id == R.id.action_settings) {
return true;
}
return super.onOptionsItemSelected(item);
}

/**
* A placeholder fragment containing a simple view.
*/
public static class PlaceholderFragment extends Fragment {
private EditText txtUserName = null;
private EditText txtPass = null;
private Button btnLogin = null;

public PlaceholderFragment() {
}
@Override
public View onCreateView(LayoutInflater inflater, ViewGroup container,
Bundle savedInstanceState) {
View rootView = inflater.inflate(R.layout.fragment_main, container,false);

txtUserName = (EditText)rootView.findViewById(R.id.txt_username);
txtPass = (EditText) rootView.findViewById(R.id.txt_pass);
btnLogin = (Button) rootView.findViewById(R.id.btn_login);

// 设置登录按钮点击事件
btnLogin.setOnClickListener(new OnClickListener() {

@Override
public void onClick(View arg0) {
String userName = txtUserName.getText().toString();
String passWord = txtPass.getText().toString();
String info = "用户名:" + userName + " 密码:" + passWord;
Toast.makeText(getActivity(), info, Toast.LENGTH_SHORT).show();

}
});
return rootView;
}

}

}