零基础学鸿蒙编程-轻量级数据库

什么是轻量级数据库

轻量级数据库是一种以键值对形式保存数据的存储方式.每条数据都需要指定一个唯一键名来进行区分.可以存储布尔型、整型、字符串等基础数据类型.其特点为简单、轻量,适合保存少量简单类型的数据,不适合保存大批量或复杂类型的数据.

基础样例

1. 写入和读取数据

1. java代码

public class MainAbilitySlice extends AbilitySlice {
    private Preferences preferences;

    @Override
    public void onStart(Intent intent) {
        super.onStart(intent);
        super.setUIContent(ResourceTable.Layout_ability_main);

        DatabaseHelper databaseHelper = new DatabaseHelper(getContext());
        String filename = "pdb";
        preferences = databaseHelper.getPreferences(filename);

        findComponentById(ResourceTable.Id_writeText).setClickedListener(component -> write());
        findComponentById(ResourceTable.Id_readText).setClickedListener(component -> read());
        findComponentById(ResourceTable.Id_modifyText).setClickedListener(component -> modify());
        findComponentById(ResourceTable.Id_delText).setClickedListener(component -> del());
    }

    private void write() {
        preferences.putString("name", "花生皮编程");
        preferences.flush();
    }

    private void read() {
        String name = preferences.getString("name", "数据不存在");
        new ToastDialog(getContext()).setText(name).show();
    }

    private void modify() {
        preferences.putString("name", "花生皮编程2");
        preferences.flush();
    }

    private void del() {
        preferences.delete("name");
    }
}

2. 对应页面布局文件:

<?xml version="1.0" encoding="utf-8"?>
<DirectionalLayout
    xmlns:ohos="http://schemas.huawei.com/res/ohos"
    ohos:height="match_parent"
    ohos:width="match_parent"
    ohos:alignment="center"
    ohos:orientation="vertical">

    <Text
        ohos:id="$ id:writeText"
        ohos:height="match_content"
        ohos:width="match_content"
        ohos:text="写数据"
        ohos:text_size="20fp"/>

    <Text
        ohos:id="$ id:readText"
        ohos:height="match_content"
        ohos:width="match_content"
        ohos:text="读数据"
        ohos:text_size="20fp"/>

    <Text
        ohos:id="$ id:modifyText"
        ohos:height="match_content"
        ohos:width="match_content"
        ohos:text="修改数据"
        ohos:text_size="20fp"/>

    <Text
        ohos:id="$ id:delText"
        ohos:height="match_content"
        ohos:width="match_content"
        ohos:text="删除数据"
        ohos:text_size="20fp"/>
</DirectionalLayout>

常用函数说明

完整源代码

https://gitee.com/hspbc/harmonyos_demos/tree/master/preferenceDemo

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