android 实现增删改查
时间: 2023-12-07 07:02:57 浏览: 30
Android 实现增删改查一般都是指对 SQLite 数据库的操作。下面是一个使用 SQLite 数据库实现增删改查的示例:
1. 创建数据库
在 `onCreate` 方法中创建数据库。
```java
public class DBHelper extends SQLiteOpenHelper {
private static final String DB_NAME = "my_database.db";
private static final int DB_VERSION = 1;
public DBHelper(Context context) {
super(context, DB_NAME, null, DB_VERSION);
}
@Override
public void onCreate(SQLiteDatabase db) {
String sql = "CREATE TABLE user ("
+ "id INTEGER PRIMARY KEY AUTOINCREMENT,"
+ "name TEXT,"
+ "age INTEGER)";
db.execSQL(sql);
}
@Override
public void onUpgrade(SQLiteDatabase db, int oldVersion, int newVersion) {
// 升级数据库
}
}
```
2. 增加数据
```java
public void addUser(String name, int age) {
SQLiteDatabase db = getWritableDatabase();
ContentValues values = new ContentValues();
values.put("name", name);
values.put("age", age);
db.insert("user", null, values);
}
```
3. 删除数据
```java
public void deleteUser(int id) {
SQLiteDatabase db = getWritableDatabase();
String whereClause = "id=?";
String[] whereArgs = {String.valueOf(id)};
db.delete("user", whereClause, whereArgs);
}
```
4. 修改数据
```java
public void updateUser(int id, String name, int age) {
SQLiteDatabase db = getWritableDatabase();
ContentValues values = new ContentValues();
values.put("name", name);
values.put("age", age);
String whereClause = "id=?";
String[] whereArgs = {String.valueOf(id)};
db.update("user", values, whereClause, whereArgs);
}
```
5. 查询数据
```java
public List<User> queryUser() {
SQLiteDatabase db = getReadableDatabase();
String[] columns = {"id", "name", "age"};
String selection = null;
String[] selectionArgs = null;
String groupBy = null;
String having = null;
String orderBy = null;
Cursor cursor = db.query("user", columns, selection, selectionArgs, groupBy, having, orderBy);
List<User> userList = new ArrayList<>();
while (cursor.moveToNext()) {
int id = cursor.getInt(cursor.getColumnIndex("id"));
String name = cursor.getString(cursor.getColumnIndex("name"));
int age = cursor.getInt(cursor.getColumnIndex("age"));
User user = new User(id, name, age);
userList.add(user);
}
cursor.close();
return userList;
}
```
以上是一个简单的示例,具体实现方式可能因项目需求而有所不同。