Android 数据存储汇总

Android 应用中常常会将一些数据保存到手机中，比如我们常见的偏好设置。将数据保存在本机，能够适配用户喜好，提供更好的用户体验。

Android 保存数据，有 4 种常见的方式：

1. 保存在内部的私有文件夹;
2. sharedPreference;
3. sd 卡的公共部分；
4. 存储到数据库中；

Android 的文件目录，分为以下几类：
1 system/app 系统自带的应用程序，无法删除。
2 data/app 用户程序安装的目录，有删除权限。安装时把apk文件复制到此目录。
3 data/data 存放应用程序的数据。Androd 会为每一个新安装的 App 生成一个目录，称为沙盒，用于保存应用程序运行时生成的数据。
4 data/dalvik-cache 将apk中的dex文件安装到 dalvik-cache 目录下(dex文件是dalvik虚拟机的可执行文件,其大小约为原始apk文件大小的四分之一)。

xml 数据的保存和读取

Android 中可以用 XmlSerializer 类生成 xml 文件格式的数据。

@Override
    public void onClick(View v) {
        String student_name = et_name.getText().toString().trim();
        String student_number = et_number.getText().toString().trim();

        int rg_id = rg_sex.getCheckedRadioButtonId();
        switch (rg_id){
            case R.id.rg_man:
                sex = "男";
                break;
            case R.id.rg_female:
                sex = "女";
                break;
            default:
                sex = "保密";
                    break;
        }

        if (TextUtils.isEmpty(student_name) || TextUtils.isEmpty(student_number) || TextUtils.isEmpty(sex)){
            Toast.makeText(this, "信息不能为空", Toast.LENGTH_SHORT).show();
            return;
        }

        XmlSerializer serializer = Xml.newSerializer();
        File file = new File(getFilesDir(), student_name+".xml");
        try {
            OutputStream os = new FileOutputStream(file);
            serializer.setOutput(os, "utf-8");

            serializer.startDocument("utf-8", true);
            serializer.startTag(null,"student");

            serializer.startTag(null, "name");
            serializer.text(student_name);
            serializer.endTag(null, "name");

            serializer.startTag(null, "sex");
            serializer.text(sex);
            serializer.endTag(null, "sex");

            serializer.startTag(null, "number");
            serializer.text(student_number);
            serializer.endTag(null, "number");

            serializer.endTag(null,"student");

            serializer.endDocument();
            os.close();
            Toast.makeText(this, "信息保存到文件成功", Toast.LENGTH_SHORT).show();
        } catch (Exception e) {
            e.printStackTrace();
        }
    }

其生成的文件内容为：

<?xml version='1.0' encoding='utf-8' standalone='yes' ?><student><name>uniapp</name><sex>男</sex><number>110</number></student>

通过XmlPullParser 类解析 xml 格式文件：

 public void onClick(View v){
        XmlPullParser pullParser = Xml.newPullParser();
        InputStream in = null;
        try {
            File file = new File(getFilesDir(), "uniapp.xml");
            pullParser.setInput(new FileInputStream(file), "utf-8");
            int eventType = pullParser.getEventType();

            Student st = null;
            while (eventType!=XmlPullParser.END_DOCUMENT){

                if (eventType== XmlPullParser.START_TAG){

                    if ("student".equals(pullParser.getName())){
                        st = new Student();
                    }
                    else if ("name".equals(pullParser.getName())){
                        String name = pullParser.nextText();
                        st.setName(name);
                    }else if ("sex".equals(pullParser.getName())){
                        String sex = pullParser.nextText();
                        st.setSex(sex);
                    }
                    else if ("number".equals(pullParser.getName())){
                        String number = pullParser.nextText();
                        st.setNumber(number);
                    }
                }

                eventType = pullParser.next();
            }

            if (st != null){
                Toast.makeText(this, st.toString(), Toast.LENGTH_LONG).show();
            }
        } catch (Exception e) {
            e.printStackTrace();
        }
    }

Android 中 SharedPreference 的存取

private SharedPreferences sp ;
    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_setting);

        LinearLayout layout_setting = findViewById(R.id.layout_setting);
        final CheckBox cb = findViewById(R.id.checkBox);
        SeekBar sb = findViewById(R.id.seekBar);
        sp =  getSharedPreferences("setting", 0);

        Boolean isChecked = sp.getBoolean("isCheck", false);
        cb.setChecked(isChecked);
        sb.setProgress(sp.getInt("progress", 0));
        layout_setting.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                cb.setChecked(!cb.isChecked());
                SharedPreferences.Editor et = sp.edit();
                et.putBoolean("isCheck", cb.isChecked());
                et.commit();
            }
        });

        sb.setOnSeekBarChangeListener(new SeekBar.OnSeekBarChangeListener() {
            @Override
            public void onProgressChanged(SeekBar seekBar, int progress, boolean fromUser) {

            }

            @Override
            public void onStartTrackingTouch(SeekBar seekBar) {

            }

            @Override
            public void onStopTrackingTouch(SeekBar seekBar) {
                sp =  getSharedPreferences("setting", 0);
                SharedPreferences.Editor et = sp.edit();
                et.putInt("progress", seekBar.getProgress());
                et.commit();
            }
        });
    }

Android 数据库的存取

Androi 中封装了 sqlitLite 数据库，继承至 SQLiteOpenHelper 即可找到使用接口：

public class StudentDbOpenHelper extends SQLiteOpenHelper {
    public StudentDbOpenHelper(Context context) {
        super(context, "student.db", null, 10);
    }

    @Override
    public void onCreate(SQLiteDatabase db) {
        db.execSQL("create table students (_id integer primary key autoincrement, _name vachar(30), " +
                "_sex varchar(10))");
    }

    @Override
    public void onUpgrade(SQLiteDatabase db, int oldVersion, int newVersion) {
//        db.execSQL("alter table students add _sex varchar(10)");
    }
}

将数据库的增删改查封装封装为操作类 StudentDao ：

public class StudentDao {


    StudentDbOpenHelper helper;

    public StudentDao(Context context) {
        helper = new StudentDbOpenHelper(context);

    }

    public void add(Student st){

        SQLiteDatabase db = helper.getWritableDatabase();
        db.execSQL("insert into students values(null,?,?)",
                new Object[]{st.getName(), st.getSex()});

//        ContentValues contentValues = new ContentValues();
//        contentValues.put("name", st.getName());
//        contentValues.put("sex", st.getSex());
//        db.insertOrThrow("students", null, contentValues)
    }
    public void delete(String id){
        SQLiteDatabase db = helper.getWritableDatabase();
        db.execSQL("delete from students where _id = ?", new Object[]{id});
    }
    public void update(Student st){
        SQLiteDatabase db = helper.getWritableDatabase();
        db.execSQL("update students set _name=?,_sex=? where _id=?", new Object[]{
            st.getName(),st.getSex(), st.getId()
        });
    }
    public Student find(String id){
        SQLiteDatabase db = helper.getReadableDatabase();
        Cursor cursor = db.rawQuery("select * from students where _id=?", new String[]{id});

        Boolean res = cursor.moveToNext();
        Student st = null;
        if (res){
             int id1 = cursor.getInt(0);
            String name = cursor.getString(1);
            String sex = cursor.getString(2);
            st = new Student(String.valueOf(id1), name, sex);
        }
        return st;
    }

    //查询所有学生信息
    public List<Student> getAll(){
        SQLiteDatabase db = helper.getReadableDatabase();
        Cursor cursor = db.rawQuery("select * from students" ,null);
        List<Student> list = new ArrayList<Student>();
        while (cursor.moveToNext()){
            Student st = new Student(String.valueOf(cursor.getInt(0)), cursor.getString(1),
                    cursor.getString(2));
            list.add(st);
        }
        return list;
    }
}

覆盖 Student 类的 toString 方法:

public class Student {
    private String id;
    private String name;
    private String sex;

    public Student(String id, String name, String sex) {
        this.id = id;
        this.name = name;
        this.sex = sex;
    }

    public String getId() {
        return id;
    }

    public void setId(String id) {
        this.id = id;
    }

    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;
    }

    @Override
    public String toString() {
        return this.getId() + " name: " + this.getName() + " sex: " + this.getSex();
    }
}

最后在 Activity 的 listView 中进行展示：

public class SqliteActivity extends AppCompatActivity {
    ListView listView;
    StudentDao sd;
    List<Student> list_students;
    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_sqlite);
        listView = findViewById(R.id.listView);
        sd = new StudentDao(this);
    }

    private MyAdapter myAdapter;
    public void onClick(View v){
        list_students = sd.getAll();
        if (myAdapter == null){
            myAdapter = new MyAdapter();
            listView.setAdapter(myAdapter);
        }else {
            myAdapter.notifyDataSetChanged();
        }

    }

    class MyAdapter extends BaseAdapter {

        @Override
        public int getCount() {
            return list_students.size();
        }

        @Override
        public Object getItem(int position) {
            return null;
        }

        @Override
        public long getItemId(int position) {
            return 0;
        }


        //position: 位置; convertView: 用于优化; parent: item 所在的父控件;
        @Override
        public View getView(int position, View convertView, ViewGroup parent) {
            View view;
            if (convertView!=null){
                view = convertView;
            }else {
                view = View.inflate(SqliteActivity.this, R.layout.item_student, null);
            }
            ImageView iv = view.findViewById(R.id.item_iv);
            TextView tv = view.findViewById(R.id.item_tv);
            final Student student = list_students.get(position);
            ImageView iv_delete = view.findViewById(R.id.iv_delete);
            iv_delete.setOnClickListener(new View.OnClickListener() {
                @Override
                public void onClick(View v) {
                    AlertDialog.Builder builder = new AlertDialog.Builder(SqliteActivity.this);
                    builder.setTitle("删除...");
                    builder.setMessage("删除吗?");
                    builder.setPositiveButton("删除", new DialogInterface.OnClickListener() {
                        @Override
                        public void onClick(DialogInterface dialog, int which) {
                            String id =  student.getId();
                            sd.delete(id);
                            Toast.makeText(SqliteActivity.this, "删除成功", Toast.LENGTH_SHORT).show();
                            SqliteActivity.this.onClick(null);
                        }
                    });
                    builder.setNegativeButton("取消", null);
                    builder.create();
                    builder.show();
                }
            });
            String sex = student.getSex();
            if ("男".equals(sex)){
                iv.setImageResource(R.drawable.nan1);
            }else {
                iv.setImageResource(R.drawable.nv);
            }
            tv.setText(position +  student.getName());
            return view;
        }
    }
}

Android 在存储数据工程中会出现的两种问题

1. oom ： 内存溢出，占用内存过高，被系统杀死；
2. memery leak: 内存泄漏，对象占用内存忘记释放；

Android 5 种进度条实现方式

//确认取消
    public void show1(View view){
        AlertDialog.Builder builder = new AlertDialog.Builder(this);
        builder.setTitle("新信息");
        builder.setMessage("约饭吗?");
        builder.setPositiveButton("约", new DialogInterface.OnClickListener() {
            @Override
            public void onClick(DialogInterface dialog, int which) {
                Toast.makeText(ListActivity.this, "可以", Toast.LENGTH_SHORT).show();
            }
        });

        builder.setNegativeButton("算了吧", null);
        builder.show();

    }
    //单选
    public void show2(View view){
        AlertDialog.Builder builder = new AlertDialog.Builder(this);
        builder.setTitle("单选");

        String[] items = {"小丽", "小红", "小芳"};
        builder.setSingleChoiceItems(items, -1, new DialogInterface.OnClickListener() {
            @Override
            public void onClick(DialogInterface dialog, int which) {
                Toast.makeText(ListActivity.this, "item is " + which, Toast.LENGTH_SHORT).show();
            }
        });
        builder.show();
    }
    //多选
    public void show3(View view){
        AlertDialog.Builder builder = new AlertDialog.Builder(this);
        builder.setTitle("单选");
        String[] items = {"小丽", "小红", "小芳"};
        final boolean[] checkdItems = {true, false, true};
        builder.setMultiChoiceItems(items, checkdItems, new DialogInterface.OnMultiChoiceClickListener() {
            @Override
            public void onClick(DialogInterface dialog, int which, boolean isChecked) {
//                checkdItems[which] = isChecked;
                Toast.makeText(ListActivity.this, "item is " + which + " " + isChecked, Toast.LENGTH_SHORT).show();
            }
        });
        builder.show();
    }
    //进度条
    public void show4(View view){
        final ProgressDialog dialog = new ProgressDialog(this);
        dialog.setMessage("正在加载中...");
        dialog.setProgressStyle(ProgressDialog.STYLE_HORIZONTAL);
        dialog.setMax(100);


        Thread t = new Thread(new Runnable() {

            @Override

            public void run() {

                try {
                    for (int i = 0; i <= 100; i=i+10){
                        Thread.sleep(1000);
                        dialog.setProgress(i);
                    }
                    //子线程沉睡
                    //让他显示10秒后，取消ProgressDialog
                } catch (InterruptedException e) {
                    e.printStackTrace();
                }
                dialog.dismiss();
            }
        });
        dialog.show();
        t.start();
    }
    //进度转盘
    public void show5(View view){

        final ProgressDialog dialog = ProgressDialog.show(this, "",

                "下载数据，请稍等 …", true, true);

        Thread t = new Thread(new Runnable() {

            @Override

            public void run() {

                try {
                    //子线程沉睡
                    Thread.sleep(10000);//让他显示10秒后，取消ProgressDialog

                } catch (InterruptedException e) {
                    e.printStackTrace();
                }
                dialog.dismiss();
            }
        });
        t.start();
    }

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