Android 数据存储方案

利用文件进行存取数据

写入文件数据

openFileOutput 是Context中提供的一个方法，用于将数据存储到指定的文件中，第一个参数是文件名，第二个参数是文件的操作模式。方法的返回一个FileOutputStream对象。

public void saveData(String input) {
    FileOutputStream fileOutputStream = null;
    BufferedWriter bufferedWriter = null;
    try {
        fileOutputStream = openFileOutput("data2022", Context.MODE_PRIVATE);
        bufferedWriter = new BufferedWriter(new OutputStreamWriter(fileOutputStream));
        bufferedWriter.write(input);
    } catch (IOException e) {
        e.printStackTrace();
    } finally {
        try {
            if (bufferedWriter != null) {
                bufferedWriter.close();
            }
        } catch (IOException e) {
            e.printStackTrace();
        }


    }
}

读取文件数据

openFileInput是Context中提供的一个方法，用于从文件中读取数据，只有一个参数（文件名称），系统会自动到/data/data//files/目录下加载这个文件，并返回一个FileInputStream对象。

public String load() {
    FileInputStream in = null;
    BufferedReader reader = null;
    StringBuilder sb = new StringBuilder();
    try {
        in = openFileInput("data2022");
        reader = new BufferedReader(new InputStreamReader(in));
        String line = "";
        while ((line = reader.readLine()) != null) {
            sb.append(line);
        }

    } catch (IOException e) {
        e.printStackTrace();
    } finally {
        if (reader != null) {
            try {
                reader.close();
            } catch (IOException e) {
                e.printStackTrace();
            }
        }
    }
    return sb.toString();
}

SharedPreferences存储

键值对存储数据

获取SharedPreferences对象：

1.Context 类中的getSharedPreferences()方法
2.Activity类中的getPreferences()方法
3.PreferenceManager类中的getDefaultSharedPreference()方法

文件生成在/data/data//shared_prefs/ 下，文件后缀是xml

findViewById(R.id.button2).setOnClickListener(v -> {
    SharedPreferences.Editor editor = getSharedPreferences("data", MODE_PRIVATE).edit();
    editor.putString("name", "Tom");
    editor.putInt("age", 28);
    editor.apply();
});

从生成的文件中取值

findViewById(R.id.button3).setOnClickListener(v -> {
    SharedPreferences preferences = getSharedPreferences("data", MODE_PRIVATE);
    String name = preferences.getString("name", "");
    int age = preferences.getInt("age", 0);
    Log.d("MainActivity", "name is :" + name);
    Log.d("MainActivity", "age is :" + age);
});

记住密码项目

SharedPreferences preferences1 = getSharedPreferences("re_data", MODE_PRIVATE);
SharedPreferences.Editor editor1 = getSharedPreferences("re_data", MODE_PRIVATE).edit();
EditText userView = findViewById(R.id.user);
EditText passView = findViewById(R.id.pass);
CheckBox check = findViewById(R.id.checkbox);


boolean rember_me = preferences1.getBoolean("rember_me", false);
if (rember_me) {
    user = preferences1.getString("user", "");
    pass = preferences1.getString("pass", "");
    editor1.putBoolean("rember_me", true);
    check.setChecked(true);
    userView.setText(user);
    passView.setText(pass);
}


findViewById(R.id.button4).setOnClickListener(v -> {
        user = userView.getText().toString();
        pass = passView.getText().toString();
    if ("admin".equals(user) && "123".equals(pass)) {
        if (check.isChecked()) {
            editor1.putString("user", user);
            editor1.putString("pass", pass);
            editor1.putBoolean("rember_me", true);
            editor1.apply();
        }else {
            editor1.putBoolean("rember_me", false);
            editor1.apply();
            // editor1.clear();
        }
        Toast.makeText(this, "已登录", Toast.LENGTH_SHORT).show();
    } else {
        userView.setText("");
        passView.setText("");
        editor1.putBoolean("rember_me", false);
        editor1.apply();
        Toast.makeText(this, "用户名或密码不对,请重新输入", Toast.LENGTH_SHORT).show();
    }


});

SQLite数据库储存

创建库

public class MydbHelper extends SQLiteOpenHelper {

public static final String CREATE_BOOK = "create table Book(id integer primary key autoincrement,author text,price real,pages integer,name text)";

@Override
public void onCreate(SQLiteDatabase db) {
    db.execSQL(CREATE_BOOK);
}

}

mydbHelper = new MydbHelper(this, "BookStore.db", null, 1);
findViewById(R.id.button).setOnClickListener(v -> {
    mydbHelper.getWritableDatabase();
});

更新

@Override
public void onUpgrade(SQLiteDatabase db, int oldVersion, int newVersion) {
    db.execSQL("drop table if exists Book");
    db.execSQL("drop table if exists Book1");
    onCreate(db);
}

增加数据

findViewById(R.id.button1).setOnClickListener(v -> {
   SQLiteDatabase db =  mydbHelper.getWritableDatabase();
   ContentValues values = new ContentValues();
    values.put("name","Thexxx");
    values.put("author","tttt");
    values.put("pages",900);
    values.put("price",10.99);
    db.insert("Book",null,values);
});

//也可以直接写SQL
db.execSQL("insert into Book (name,author,pages,price) values(?,?,?,?)",new String[]{"123","123","123","123"});

更新数据

findViewById(R.id.button2).setOnClickListener(v -> {
    SQLiteDatabase db =  mydbHelper.getWritableDatabase();
    ContentValues values = new ContentValues();
    values.put("author","tom");
   db.update("Book",values,"pages < ?",new String[]{"600"});

});
//也可以直接写SQL
db.execSQL("update Book set name =? where price = ?",new  String[]{"Tom","123"});

删除数据

findViewById(R.id.button3).setOnClickListener(v -> {
    SQLiteDatabase db =  mydbHelper.getWritableDatabase();
    db.delete("Book","pages < ?",new String[]{"600"});
});
//也可以直接写SQL
db.execSQL("delete from Book where pages < ?",new  String[]{"200"});

查询数据

findViewById(R.id.button4).setOnClickListener(v -> {
    SQLiteDatabase db =  mydbHelper.getWritableDatabase();
    Cursor cursor = db.query("Book", null, null, null, null, null, null);
    if(cursor.moveToFirst()){
        do{
             String name = cursor.getString(cursor.getColumnIndexOrThrow("name"));
            Log.d("MainActivity","book name is " + name);
        }while (cursor.moveToNext());
    }

    cursor.close();

});
//也可以直接写SQL
Cursor cursor = db.rawQuery("select * from Book", null);

LitePal操作数据库

** 依赖加载问题，后期补学 **