MainActivity 访问 fragment_main.xml 中的组件 空指针

最近开始学习Android开发，遇到MainActivity 访问 fragment_main.xml 中的组件空指针问题，各种查资料，没找到好的完整解决方法，只好自己写一个，Activity生命周期还没深入理解，可能存在问题，请大家见谅！最近学习感觉就像又开始搞web前台了-_-!

package com.example.translatedatabyintent;

import java.util.zip.Inflater;

import android.support.v7.app.ActionBarActivity;
import android.support.v7.app.ActionBar;
import android.support.v4.app.Fragment;
import android.text.StaticLayout;
import android.app.Activity;
import android.content.Context;
import android.content.Intent;
import android.os.Bundle;
import android.view.LayoutInflater;
import android.view.Menu;
import android.view.MenuItem;
import android.view.View;
import android.view.ViewGroup;
import android.widget.Button;
import android.os.Build;

public class MainActivity extends ActionBarActivity {

	private Button button;
	private static Fragment fragment;
	@Override
	protected void onStart(){
		super.onStart();
		button = (Button)fragment.getView().findViewById(R.id.button1);//根据id查找到某一视图
		//绑定事件
		button.setOnClickListener(new View.OnClickListener() {
			
			@Override
			public void onClick(View v) {
				// TODO Auto-generated method stub
			    Intent intent = new Intent(MainActivity.this,OtherActivity.class);
			    //意图中传递数据
			    intent.putExtra("name","张三");
			    intent.putExtra("age",23);
			    intent.putExtra("address","北京");
			    //启动意图
			    startActivity(intent);
			    
			}
		});
	}
	@Override
	protected void onCreate(Bundle savedInstanceState) {
		super.onCreate(savedInstanceState);
		setContentView(R.layout.activity_main);//加载布局文件
		//加载布局
		if (savedInstanceState == null) {
			fragment =new PlaceholderFragment();
			getSupportFragmentManager().beginTransaction()
					.add(R.id.container,fragment).commit();
		}
		//View rootView =Inflater.inflate()
	
	}

	@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.
	 */
	//加载碎片！
	public static class PlaceholderFragment extends Fragment {

		public PlaceholderFragment() {
		}

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

}