Andorid基础--------数据处理

数据持久化

有些信息需要保存在本地

三种方法  
1.保存在文件中，需要的时候进行读写   io 比较复杂麻烦 不推荐使用
2.保存在SharedPreFerence中
3.保存在数据库中SQLite


第一种方法是java中的方法，利用流将要保存的数据写入到某个目录下的文件中，在需要的时候进行读写。
Android 中提供了一种openFileoutput()的方法  用这种方法可以将流写入指定文件中


第二种方法 是保存在SharedPreFrence
SharedPrefrenc是android 提供的一种 存储方式  使用较为简单

这里提供一个工具类可以更好的使用


 public static class UserInfoSpUtils{
        public final static String SP_NAME = "userinfo";
        private static SharedPreferences sp;

        public static void saveBoolean(Context context, String key, boolean value) {
            if (sp == null)
                sp = context.getSharedPreferences(SP_NAME, 0);
            sp.edit().putBoolean(key, value).commit();
        }

        public static void saveInt(Context context, String key, int value) {
            if (sp == null)
                sp = context.getSharedPreferences(SP_NAME, 0);
            sp.edit().putInt(key, value).commit();
        }

        public static void saveLong(Context context, String key, Long value) {
            if (sp == null)
                sp = context.getSharedPreferences(SP_NAME, 0);
            sp.edit().putLong(key, value).commit();
        }

        public static void saveString(Context context, String key, String value) {
            if (sp == null)
                sp = context.getSharedPreferences(SP_NAME, 0);
            sp.edit().putString(key, value).commit();
        }

        public static int getInt(Context context, String key, int defValue) {
            if (sp == null)
                sp = context.getSharedPreferences(SP_NAME, 0);
            return sp.getInt(key, defValue);
        }

        public static String getString(Context context, String key, String defValue) {
            if (sp == null)
                sp = context.getSharedPreferences(SP_NAME, 0);
            return sp.getString(key, defValue);
        }

        public static boolean getBoolean(Context context, String key,
                                         boolean defValue) {
            if (sp == null)
                sp = context.getSharedPreferences(SP_NAME, 0);
            return sp.getBoolean(key, defValue);
        }

        public static Long getLong(Context context, String key, Long defValue) {
            if (sp == null)
                sp = context.getSharedPreferences(SP_NAME, 0);
            return sp.getLong(key, defValue);
        }
    }


第三种  数据库 SQLite

android 中提供了一个SQLiteOpenHelper 类用来创建数据库  


代码

public class StatOpenHelper extends SQLiteOpenHelper {
    //部门数据库表格
    private final  String departmentSQL = "CREATE TABLE IF NOT EXISTS DepartmentFee(" +
            "amount TEXT," +//金额
            "accountName TEXT," +//报销科目
            "expenseId  TEXT," +//单据id
            "accountId TEXT," +//科目id
            "month TEXT," +//月
            "year TEXT," +//年
            "departmentId TEXT," +// ID
            "departmentCode TEXT," +//code
            "departmentName TEXT," +//部门名称
            "date TEXT," +//时间
            "type TEXT" +//统计类型
            ")";
    //事业部数据库表格
    private final String businessUnitSQL = "CREATE TABLE IF NOT EXISTS BusinessUnitFee(" +
            "amount TEXT," +
            "businessUnitCode  TEXT," +
            "expenseId  TEXT," +
            "accountName   TEXT," +
            "accountId  TEXT," +
            "businessUnitName  TEXT," +
            "businessUnitId  TEXT," +
            "month  TEXT," +
            "year  TEXT," +
            "date  TEXT," +
            "type  TEXT" +
            ")";
    //客户数据库表格
    private final String clientSQL = "CREATE TABLE IF NOT EXISTS ClientFee(" +
            "amount TEXT," +
            "accountName  TEXT," +
            "accountId   TEXT," +
            "clientCode  TEXT," +
            "clientName  TEXT," +
            "month  TEXT," +
            "year  TEXT," +
            "date  TEXT," +
            "type  TEXT," +
            "clientId  TEXT" +
            ")";
    //项目数据库表格
    private final String projectSQL = "CREATE TABLE IF NOT EXISTS ProjectFee(" +
            "amount TEXT," +
            "accountName  TEXT," +
            "accountId   TEXT," +
            "projectCode  TEXT," +
            "month  TEXT," +
            "year  TEXT," +
            "projectId  TEXT," +
            "date  TEXT," +
            "type  TEXT," +
            "projectName  TEXT" +
            ")";

    public StatOpenHelper(Context context, String name, SQLiteDatabase.CursorFactory factory, int version) {
        super(context, name, factory, version);
    }

    public StatOpenHelper(Context context, String name, SQLiteDatabase.CursorFactory factory, int version, DatabaseErrorHandler errorHandler) {
        super(context, name, factory, version, errorHandler);
    }

    @Override
    public void onCreate(SQLiteDatabase db) {

        String sql=
              "CREATE TABLE IF NOT EXISTS DepartmentFee(amount TEXT,accountName TEXT,expenseId  TEXT,accountId TEXT,month TEXT,year TEXT,departmentId TEXT,departmentCode TEXT,departmentName TEXT,date TEXT,type TEXT)"
      
        db.execSQL(sql);
    }

    //该方法用于数据库升级时使用
    @Override
    public void onUpgrade(SQLiteDatabase db, int oldVersion, int newVersion) {
       
    }
}




基本增删改查  

增 insert方法  
 
ContentValues cv = new ContentValues();//实例化一个ContentValues用来装载待插入的数据cv.put("username","Jack Johnson");//添加用户名
cv.put("password","iLovePopMusic"); //添加密码
db.insert("user",null,cv);//执行插入操作


删 delete

String whereClause = "username=?";//删除的条件
String[] whereArgs = {"Jack Johnson"};//删除的条件参数
db.delete("user",whereClause,whereArgs);//执行删除

改
ContentValues cv = new ContentValues();//实例化ContentValues
cv.put("password","iHatePopMusic");//添加要更改的字段及内容
String whereClause = "username=?";//修改条件
String[] whereArgs = {"Jack Johnson"};//修改条件的参数
db.update("user",cv,whereClause,whereArgs);//执行修改

查

数据查询相对前面几种方法就复杂一些了，因为查询会带有很多条件

通过query实现查询的

public Cursor query(String table, String[] columns, String selection, String[] selectionArgs, String groupBy, String having, String orderBy, String limit)

各参数说明：

    table：表名称
    colums：列名称数组
    selection：条件子句，相当于where
    selectionArgs：条件语句的参数数组
    groupBy：分组
    having：分组条件
    orderBy：排序类
    limit：分页查询的限制
    Cursor：返回值，相当于结果集ResultSet


使用数据库的时候最好开启事务
db.beginTransaction()
开启事务
db.setTransactionSuccessful()
成功
db.endTransaction  
结束事务

事务一定要结束 最好使用try{}catch{}finally{}的方式 让结束事务在finally中


升级数据库  

 sqldrop = "DROP TABLE SearchRecord";
            db.execSQL(sqldrop);


删掉之前的表

数据库升级最佳写法

@Override
public void onUpgrade(SQLiteDatabase db, int oldVersion, int newVersion) {
    switch (oldVersion) {
        case 1:
            db.execSQL(CREATE_CATEGORY);
        case 2:
            db.execSQL("alter table Book add column category_id integer");
        default:
    }
}

注意 上述数据库升级方法中的switch方法中没有写break 并不是忘记写，而是要保证内部的方法都执行到  预防跨版本升级的问题