利用Android studio 文件存储

在Android Studio中存储文件有多种方式，包括内部存储、外部存储、SQLite数据库等。下面是一些常用的方法：

1. 内部存储

使用内部存储可以将文件保存在应用程序私有目录中，其他应用程序无法访问该目录。以下是一些示例代码：

- 写入文件：

String filename = "myfile";
String fileContents = "Hello world!";
try (FileOutputStream fos = openFileOutput(filename, Context.MODE_PRIVATE)) {
    fos.write(fileContents.getBytes());
} catch (IOException e) {
    e.printStackTrace();
}

- 读取文件：

String filename = "myfile";
try (FileInputStream fis = openFileInput(filename)) {
    InputStreamReader inputStreamReader = new InputStreamReader(fis);
    BufferedReader bufferedReader = new BufferedReader(inputStreamReader);
    StringBuilder stringBuilder = new StringBuilder();
    String line;
    while ((line = bufferedReader.readLine()) != null) {
        stringBuilder.append(line).append('\n');
    }
    String fileContents = stringBuilder.toString();
} catch (IOException e) {
    e.printStackTrace();
}

2. 外部存储

使用外部存储可以将文件保存在SD卡中，其他应用程序也可以访问该目录。以下是一些示例代码：

- 检查是否有权限：

if (ContextCompat.checkSelfPermission(this, Manifest.permission.WRITE_EXTERNAL_STORAGE)
        != PackageManager.PERMISSION_GRANTED) {
    ActivityCompat.requestPermissions(this, new String[]{Manifest.permission.WRITE_EXTERNAL_STORAGE}, 1);
}

- 写入文件：

File file = new File(Environment.getExternalStorageDirectory(), "myfile");
String fileContents = "Hello world!";
try (FileOutputStream fos = new FileOutputStream(file)) {
    fos.write(fileContents.getBytes());
} catch (IOException e) {
    e.printStackTrace();
}

- 读取文件：

File file = new File(Environment.getExternalStorageDirectory(), "myfile");
try (FileInputStream fis = new FileInputStream(file)) {
    InputStreamReader inputStreamReader = new InputStreamReader(fis);
    BufferedReader bufferedReader = new BufferedReader(inputStreamReader);
    StringBuilder stringBuilder = new StringBuilder();
    String line;
    while ((line = bufferedReader.readLine()) != null) {
        stringBuilder.append(line).append('\n');
    }
    String fileContents = stringBuilder.toString();
} catch (IOException e) {
    e.printStackTrace();
}

3. SQLite数据库

SQLite是一种轻量级的关系型数据库，常用于存储结构化的数据。以下是一些示例代码：

- 创建数据库：

public class MyDatabaseHelper extends SQLiteOpenHelper {
    private static final String DATABASE_NAME = "mydatabase.db";
    private static final int DATABASE_VERSION = 1;

    public MyDatabaseHelper(Context context) {
        super(context, DATABASE_NAME, null, DATABASE_VERSION);
    }

    @Override
    public void onCreate(SQLiteDatabase db) {
        db.execSQL("CREATE TABLE IF NOT EXISTS mytable (_id INTEGER PRIMARY KEY AUTOINCREMENT, name TEXT, age INTEGER)");
    }

    @Override
    public void onUpgrade(SQLiteDatabase db, int oldVersion, int newVersion) {
        db.execSQL("DROP TABLE IF EXISTS mytable");
        onCreate(db);
    }
}

- 插入数据：

MyDatabaseHelper dbHelper = new MyDatabaseHelper(this);
SQLiteDatabase db = dbHelper.getWritableDatabase();

ContentValues values = new ContentValues();
values.put("name", "John");
values.put("age", 25);
db.insert("mytable", null, values);

db.close();

- 查询数据：

MyDatabaseHelper dbHelper = new MyDatabaseHelper(this);
SQLiteDatabase db = dbHelper.getReadableDatabase();

String[] projection = {"_id", "name", "age"};
Cursor cursor = db.query("mytable", projection, null, null, null, null, null);

while (cursor.moveToNext()) {
    int id = cursor.getInt(cursor.getColumnIndex("_id"));
    String name = cursor.getString(cursor.getColumnIndex("name"));
    int age = cursor.getInt(cursor.getColumnIndex("age"));
}

cursor.close();
db.close();

希望这些示例代码能够帮助你在Android Studio中存储文件。