android（12）（简单学生管理系统，包括文件写入SD卡，pull解析xml文件等）

1.布局代码：
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:background="@android:color/white"
    android:orientation="vertical" >

    <TextView
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_gravity="center_horizontal"
        android:layout_marginTop="5dip"
        android:text="学生管理系统"
        android:textColor="#99CCFF"
        android:textSize="23sp" />

    <RelativeLayout
        android:layout_width="fill_parent"
        android:layout_height="wrap_content"
        android:layout_marginTop="5dip"
        android:padding="5dip" >

        <TextView
            android:id="@+id/tv_name"
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:paddingLeft="15dip"
            android:paddingRight="15dip"
            android:text="姓名"
            android:textSize="18sp" />

        <TextView
            android:id="@+id/tv_sex"
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:layout_marginLeft="5dip"
            android:layout_toRightOf="@id/tv_name"
            android:paddingLeft="15dip"
            android:paddingRight="15dip"
            android:text="性别"
            android:textSize="18sp" />

        <TextView
            android:id="@+id/tv_age"
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:layout_marginLeft="5dip"
            android:layout_toRightOf="@id/tv_sex"
            android:paddingLeft="15dip"
            android:paddingRight="15dip"
            android:text="年龄"
            android:textSize="18sp" />

        <EditText
            android:id="@+id/et_name"
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:layout_alignLeft="@id/tv_name"
            android:layout_alignRight="@id/tv_name"
            android:layout_below="@id/tv_name"
            android:singleLine="true" />

        <EditText
            android:id="@+id/et_sex"
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:layout_alignLeft="@id/tv_sex"
            android:layout_alignRight="@id/tv_sex"
            android:layout_below="@id/tv_sex"
            android:singleLine="true" />

        <EditText
            android:id="@+id/et_age"
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:layout_alignLeft="@id/tv_age"
            android:layout_alignRight="@id/tv_age"
            android:layout_below="@id/tv_age"
            android:inputType="number"
            android:singleLine="true" />

        <Button
            android:id="@+id/btn_add_student"
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:layout_alignBaseline="@id/et_age"
            android:layout_toRightOf="@id/et_age"
            android:text="添加学生"
            android:textSize="20sp" />
    </RelativeLayout>

    <ScrollView
        android:layout_width="fill_parent"
        android:layout_height="wrap_content"
        android:layout_weight="1" >

        <LinearLayout
            android:id="@+id/ll_student_list"
            android:layout_width="fill_parent"
            android:layout_height="fill_parent"
            android:layout_margin="1dip"
            android:orientation="vertical"
            android:padding="5dip" >
        </LinearLayout>
    </ScrollView>

    <LinearLayout
        android:layout_width="fill_parent"
        android:layout_height="wrap_content"
        android:layout_marginTop="5dip"
        android:orientation="horizontal" >

        <Button
            android:id="@+id/btn_save"
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:layout_weight="1"
            android:text="保存数据"
            android:textSize="20sp" />

        <Button
            android:id="@+id/btn_restore"
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:layout_weight="1"
            android:text="恢复数据"
            android:textSize="20sp" />
    </LinearLayout>

</LinearLayout>
entities类：
public class Student {

    private String name;
    private String sex;
    private Integer age;
    public Student(String name, String sex, Integer age) {
        super();
        this.name = name;
        this.sex = sex;
        this.age = age;
    }
    public Student() {
        super();
        // TODO Auto-generated constructor stub
    }
    public String getName() {
        return name;
    }
    public void setName(String name) {
        this.name = name;
    }
    public String getSex() {
        return sex;
    }
    public void setSex(String sex) {
        this.sex = sex;
    }
    public Integer getAge() {
        return age;
    }
    public void setAge(Integer age) {
        this.age = age;
    }
    @Override
    public String toString() {
        return "Student [name=" + name + ", sex=" + sex + ", age=" + age + "]";
    }
业务逻辑代码：
public class MainActivity extends Activity implements OnClickListener {

    private EditText etName;
    private EditText etSex;
    private EditText etAge;
    private LinearLayout llStudentList;
    private List<Student> studentList;
    private String filePath;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        //初始化操作
        init();
    }
     //初始化操作
    private void init() {
        etName = (EditText) findViewById(R.id.et_name);
        etSex = (EditText) findViewById(R.id.et_sex);
        etAge = (EditText) findViewById(R.id.et_age);

        llStudentList = (LinearLayout) findViewById(R.id.ll_student_list);

        findViewById(R.id.btn_save).setOnClickListener(this);
        findViewById(R.id.btn_restore).setOnClickListener(this);
        findViewById(R.id.btn_add_student).setOnClickListener(this);

        studentList = new ArrayList<Student>();
        filePath = Environment.getExternalStorageDirectory().getPath() + "/student.xml";//数据保存在SD卡的一个student的xml文件中。
    }
    //点击事件
    @Override
    public void onClick(View v) {
        switch (v.getId()) {
        case R.id.btn_save://如果点击的是保存数据按钮
            if(studentList.size() > 0) {
                if(saveStudent2Local()) {
                    Toast.makeText(this, "保存成功", 0).show();
                } else {
                    Toast.makeText(this, "保存失败", 0).show();
                }
            } else {
                Toast.makeText(this, "当前没有数据", 0).show();
            }
            break;
        case R.id.btn_restore://如果点击的是恢复数据的按钮
            if(restoreStudentFromLocal()) {
                Toast.makeText(this, "恢复成功", 0).show();
            } else {
                Toast.makeText(this, "恢复失败", 0).show();
            }
            break;
        case R.id.btn_add_student://如果点击的是添加学生的按钮。
            addStudent();
            break;
        default:
            break;
        }
    }
    //从本地恢复学生信息（xml解析）
    private boolean restoreStudentFromLocal() {
        try {
            XmlPullParser parser = Xml.newPullParser();
            parser.setInput(new FileInputStream(filePath), "utf-8");

            int eventType = parser.getEventType();

            studentList.clear();

            Student student = null;
            String nodeName = null;
            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) {
            e.printStackTrace();
        }
        return false;
    }
    //刷新学生集合（把添加的学生显示在ScrollView中）
    private void refreshStudentList() {
        llStudentList.removeAllViews();//先把屏幕上所有的数据移除
        TextView childView;
        for (Student student : studentList) {
            childView = new TextView(this);
            childView.setTextSize(23);
            childView.setTextColor(Color.BLACK);
            childView.setText("　　" + student.getName() + "　　" + student.getSex() + "　　" + student.getAge());
            llStudentList.addView(childView);
        }
    }
    //保存数据到SD卡。
    private boolean saveStudent2Local() {
        try {
            XmlSerializer serializer = Xml.newSerializer();
            serializer.setOutput(new FileOutputStream(filePath), "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) {
            e.printStackTrace();
        }
        return false;
    }
    //添加学生
    private void addStudent() {
        String name = etName.getText().toString();
        String sex = etSex.getText().toString();
        String age = etAge.getText().toString();

        if(!TextUtils.isEmpty(name) 
                && !TextUtils.isEmpty(sex) 
                && !TextUtils.isEmpty(age)) {
            studentList.add(new Student(name, sex, Integer.valueOf(age)));
            TextView childView = new TextView(this);
            childView.setTextSize(23);
            childView.setTextColor(Color.BLACK);
            childView.setText("　　" + name + "　　" + sex + "　　" + age);
            llStudentList.addView(childView);
        } else {
            Toast.makeText(this, "请正确输入", 0).show();
        }
    }