linearLayout在代码中的使用

package com.heima.student_manage;import java.io.File;import java.io.FileInputStream;import java.io.FileNotFoundException;import java.io.FileOutputStream;import java.util.ArrayList;import java.util.List;import org.xmlpull.v1.XmlPullParser;import org.xmlpull.v1.XmlSerializer;import com.heima.student_manage.entities.Student;import android.app.Activity;import android.os.Bundle;import android.os.Environment;import android.text.TextUtils;import android.util.Xml;import android.view.View;import android.view.View.OnClickListener;import android.widget.Button;import android.widget.EditText;import android.widget.LinearLayout;import android.widget.TextView;import android.widget.Toast;public class Student_manageActivity extends Activity implements OnClickListener{    /** Called when the activity is first created. */	private EditText name_mes;	private EditText sex_mes;	private EditText age_mes;	private Button add_student;	private Button save_student;	private Button restore_student;	LinearLayout llStudentList = null;	List
    
      studentlist = null;	String path = "";    @Override    public void onCreate(Bundle savedInstanceState) {        super.onCreate(savedInstanceState);        setContentView(R.layout.main);                //先根据id获取所有键        init();                  }	private void init() {		// TODO Auto-generated method stub		name_mes = (EditText) findViewById(R.id.name_mes);		sex_mes = (EditText) findViewById(R.id.sex_mes);		age_mes = (EditText) findViewById(R.id.age_mes);		add_student = (Button) findViewById(R.id.bt_add);		save_student = (Button) findViewById(R.id.btn_save);		restore_student = (Button) findViewById(R.id.btn_restore);		llStudentList = (LinearLayout) findViewById(R.id.ll_student_list);		  //为按钮设置监听器        add_student.setOnClickListener(this);        save_student.setOnClickListener(this);        restore_student.setOnClickListener(this);                studentlist = new ArrayList
     
      ();        path = Environment.getExternalStorageDirectory().getPath() + "/student.xml";	}	@Override	public void onClick(View v) {		// TODO Auto-generated method stub		switch (v.getId()) {		case R.id.bt_add:			addStudent();			break;		case R.id.btn_save:			if(studentlist.size()>0){				if(savetudent()){					Toast.makeText(this, "保存成功", 0).show();				}else{					Toast.makeText(this, "保存失败", 0).show();				}			}else{				Toast.makeText(this, "暂无数据", 0).show();			}			break;		case R.id.btn_restore:			if(restoreStudentFromLocal()) {				Toast.makeText(this, "恢复成功", 0).show();			} else {				Toast.makeText(this, "恢复失败", 0).show();			}			break;		default:			break;		}	}	private boolean restoreStudentFromLocal() {		// TODO Auto-generated method stub				try {			File file = new File(path);			FileInputStream fis = new FileInputStream(file);			studentlist.clear();			XmlPullParser parser = Xml.newPullParser();			parser.setInput(fis, "utf-8");			Student student = null;			int eventType = parser.getEventType();			String nodeName = "";			while(eventType != XmlPullParser.END_DOCUMENT) {				nodeName = parser.getName();				switch (eventType) {				case XmlPullParser.START_TAG:					if("student".equals(nodeName)) {						student = new Student();					} else if("name".equals(nodeName)) {						student.setName(parser.nextText());					} else if("sex".equals(nodeName)) {						student.setSex(parser.nextText());					} else if("age".equals(nodeName)) {						student.setAge(Integer.valueOf(parser.nextText()));					}					break;				case XmlPullParser.END_TAG:					if("student".equals(nodeName)) {						studentlist.add(student);					}					break;				default:					break;				}				eventType = parser.next();			}			refreshStudentList();						return true;								} catch (Exception e) {			// TODO Auto-generated catch block			e.printStackTrace();		}						return false;	}	private void refreshStudentList() {		// TODO Auto-generated method stub		//		llStudentList.removeAllViews();		TextView textview = null;		for(Student student : studentlist){			//添加到界面上			textview = new TextView(this);			textview.setText("　　" + student.getName() + "　　　　" + student.getSex() + "　　　　" + student.getAge());			llStudentList.addView(textview);		}	}	private boolean savetudent() {		// TODO Auto-generated method stub				try {			FileOutputStream fos = new FileOutputStream(path);						XmlSerializer serializer = Xml.newSerializer();			serializer.setOutput(fos, "utf-8");						serializer.startDocument("utf-8", true);			serializer.startTag(null, "infos");			for (Student stu : studentlist) {				serializer.startTag(null, "student");								serializer.startTag(null, "name");				serializer.text(stu.getName());				serializer.endTag(null, "name");				serializer.startTag(null, "sex");				serializer.text(stu.getSex());				serializer.endTag(null, "sex");				serializer.startTag(null, "age");				serializer.text(String.valueOf(stu.getAge()));				serializer.endTag(null, "age");								serializer.endTag(null, "student");			}			serializer.endTag(null, "infos");			serializer.endDocument();			return true;		} catch (Exception e) {			// TODO Auto-generated catch block			e.printStackTrace();		}						return false;	}	private void addStudent() {		// TODO Auto-generated method stub		String name = name_mes.getText().toString();		String sex = sex_mes.getText().toString();		String age = age_mes.getText().toString();				if(!TextUtils.isEmpty(name) && !TextUtils.isEmpty(sex) && !TextUtils.isEmpty(age)){			//添加到学生列表    			Student student = new Student(name, sex, Integer.valueOf(age));			studentlist.add(student);			//添加到界面上			TextView textview = new TextView(this);			textview.setText("　　" + name + "　　　　" + sex + "　　　　" + age);			llStudentList.addView(textview);		}else{			Toast.makeText(this, "请正确输入", 0).show();		}	}}