HarmonyOS 鸿蒙Next 元服务对JSON的读写操作示例

import dataPreferences from '@ohos.data.preferences';  
import { BusinessError } from '@ohos.base';  
/**

JSON数据操作服务类

*/

export class JsonStorageService {

private static instance: JsonStorageService;

private preferences: dataPreferences.Preferences | null = null;

private static readonly PREFERENCES_NAME = ‘app_storage’;

// 单例模式  
private constructor() {}
public static getInstance(): JsonStorageService {

if (!JsonStorageService.instance) {

JsonStorageService.instance = new JsonStorageService();

}

return JsonStorageService.instance;

}
/**

初始化存储服务
@param context 上下文
@returns Promise<void>

*/

public async initialize(context: Context): Promise<void> {

try {

if (!this.preferences) {

this.preferences = await dataPreferences.getPreferences(context, JsonStorageService.PREFERENCES_NAME);

console.log(‘Storage service initialized successfully’);

}

} catch (error) {

console.error(‘Failed to initialize storage service:’, error);

throw error;

}

}

/**


存储JSON数据


@param key 键


@param value 值


@returns Promise<void>

*/

public async putJson<T>(key: string, value: T): Promise<void> {

try {

if (!this.preferences) {

throw new Error(‘Storage service not initialized’);

}
// 将对象转换为JSON字符串  
const jsonString = JSON.stringify(value);

await this.preferences.put(key, jsonString);

await this.preferences.flush();

console.log(Successfully stored data <span class="hljs-keyword">for</span> key: ${key});

} catch (error) {

console.error(Failed to store data <span class="hljs-keyword">for</span> key ${key}:, error);

throw error;

}

}


/**


读取JSON数据


@param key 键


@param defaultValue 默认值


@returns Promise<T>

*/

public async getJson<T>(key: string, defaultValue: T): Promise<T> {

try {

if (!this.preferences) {

throw new Error(‘Storage service not initialized’);

}
const jsonString = await this.preferences.get(key, JSON.stringify(defaultValue));

return JSON.parse(jsonString as string) as T;

} catch (error) {

console.error(Failed to retrieve data <span class="hljs-keyword">for</span> key ${key}:, error);

return defaultValue;

}

}


/**


删除指定键的数据


@param key 键


@returns Promise<void>

*/

public async delete(key: string): Promise<void> {

try {

if (!this.preferences) {

throw new Error(‘Storage service not initialized’);

}
await this.preferences.delete(key);

await this.preferences.flush();

console.log(Successfully deleted data <span class="hljs-keyword">for</span> key: ${key});

} catch (error) {

console.error(Failed to <span class="hljs-keyword">delete</span> data <span class="hljs-keyword">for</span> key ${key}:, error);

throw error;

}

}


/**


清除所有数据


@returns Promise<void>

*/

public async clear(): Promise<void> {

try {

if (!this.preferences) {

throw new Error(‘Storage service not initialized’);

}
await this.preferences.clear();

await this.preferences.flush();

console.log(‘Successfully cleared all data’);

} catch (error) {

console.error(‘Failed to clear data:’, error);

throw error;

}

}


/**


检查键是否存在


@param key 键


@returns Promise<boolean>

*/

public async hasKey(key: string): Promise<boolean> {

try {

if (!this.preferences) {

throw new Error(‘Storage service not initialized’);

}
return await this.preferences.has(key);

} catch (error) {

console.error(Failed to check key ${key}:, error);

return false;

}

}

}


// 使用示例  
@Entry

@Component

struct Index {

private storage: JsonStorageService = JsonStorageService.getInstance();

@State userData: UserData = { name: ‘’, age: 0 };
// 示例数据接口  
interface UserData {

name: string;

age: number;

}
async aboutToAppear() {

try {

// 初始化存储服务  
await this.storage.initialize(getContext(this));
  <span class="hljs-comment">// 存储示例数据  </span>
  <span class="hljs-keyword">const</span> testData: UserData = {  
    name: <span class="hljs-string">"张三"</span>,  
    age: <span class="hljs-number">25</span>  
  };  
  await <span class="hljs-keyword">this</span>.storage.putJson(<span class="hljs-string">'user_data'</span>, testData);  

  <span class="hljs-comment">// 读取数据  </span>
  <span class="hljs-keyword">this</span>.userData = await <span class="hljs-keyword">this</span>.storage.getJson&lt;UserData&gt;(<span class="hljs-string">'user_data'</span>, { name: <span class="hljs-string">''</span>, age: <span class="hljs-number">0</span> });  
} <span class="hljs-keyword">catch</span> (error) {  
  console.error(<span class="hljs-string">'Failed to initialize or operate storage:'</span>, error);  
}  
}
build() {

Column() {

// 显示存储的数据  
Text(姓名: ${<span class="hljs-keyword">this</span>.userData.name})

.fontSize(20)

.margin(10)
  Text(`年龄: ${<span class="hljs-keyword">this</span>.userData.age}`)  
    .fontSize(<span class="hljs-number">20</span>)  
    .margin(<span class="hljs-number">10</span>)  

  <span class="hljs-comment">// 存储新数据的按钮  </span>
  Button(<span class="hljs-string">'保存新数据'</span>)  
    .onClick(async () =&gt; {  
      <span class="hljs-keyword">const</span> newData: UserData = {  
        name: <span class="hljs-string">"李四"</span>,  
        age: <span class="hljs-number">30</span>  
      };  
      await <span class="hljs-keyword">this</span>.storage.putJson(<span class="hljs-string">'user_data'</span>, newData);  
      <span class="hljs-keyword">this</span>.userData = await <span class="hljs-keyword">this</span>.storage.getJson&lt;UserData&gt;(<span class="hljs-string">'user_data'</span>, { name: <span class="hljs-string">''</span>, age: <span class="hljs-number">0</span> });  
    })  
    .margin(<span class="hljs-number">10</span>)  

  <span class="hljs-comment">// 清除数据的按钮  </span>
  Button(<span class="hljs-string">'清除数据'</span>)  
    .onClick(async () =&gt; {  
      await <span class="hljs-keyword">this</span>.storage.clear();  
      <span class="hljs-keyword">this</span>.userData = { name: <span class="hljs-string">''</span>, age: <span class="hljs-number">0</span> };  
    })  
    .margin(<span class="hljs-number">10</span>)  
}  
.width(<span class="hljs-string">'100%'</span>)  
.height(<span class="hljs-string">'100%'</span>)  
.justifyContent(FlexAlign.Center)  
}

}

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