如何将List <Object>保存到SharedPreferences？

Question

我有一个产品列表,我从webservice检索,当应用程序第一次打开时,应用程序从webservice获取产品列表.我想将此列表保存到共享首选项.

    List<Product> medicineList = new ArrayList<Product>();

产品类是:

public class Product {
    public final String productName;
    public final String price;
    public final String content;
    public final String imageUrl;

    public Product(String productName, String price, String content, String imageUrl) {
        this.productName = productName;
        this.price = price;
        this.content = content;
        this.imageUrl = imageUrl;
    }
}

我如何保存此列表不是每次都从webservice请求？

Answer 1

它只能使用原始类型,因为首选项保留在内存中.但你可以使用的是将你的类型用Gson序列化为json并将字符串放入首选项:

private static SharedPreferences sharedPreferences = context.getSharedPreferences(STORE_FILE_NAME, Context.MODE_PRIVATE);

private static SharedPreferences.Editor editor = sharedPreferences.edit();

public <T> void setList(String key, List<T> list) {
    Gson gson = new Gson();
    String json = gson.toJson(list);

    set(key, json);
}

public static void set(String key, String value) {
    editor.putString(key, value);
    editor.commit();
}

Answer 2

您可以使用GSON转换对象 - > JSON(.toJSON)和JSON - >对象(.fromJSON).

• 您想要定义标签(例如):

  private static final String PREFS_TAG = "SharedPrefs";
  private static final String PRODUCT_TAG = "MyProduct";
  

• 获取这些标记的sharedPreference

  private List<Product> getDataFromSharedPreferences(){
      Gson gson = new Gson();
      List<Product> productFromShared = new ArrayList<>();
      SharedPreferences sharedPref = getApplicationContext().getSharedPreferences(PREFS_TAG, Context.MODE_PRIVATE);
      String jsonPreferences = sharedPref.getString(PRODUCT_TAG, "");    
  
      Type type = new TypeToken<List<Product>>() {}.getType();
      productFromShared = gson.fromJson(jsonPreferences, type);
  
      return preferences;
  }
  

• 设置您的sharedPreferences

  private void setDataFromSharedPreferences(Product curProduct){
      Gson gson = new Gson();
      String jsonCurProduct = gson.toJson(curProduct);
  
      SharedPreferences sharedPref = getApplicationContext().getSharedPreferences(PREFS_TAG, Context.MODE_PRIVATE);
      SharedPreferences.Editor editor = sharedPref.edit();
  
      editor.putString(PRODUCT_TAG, jsonCurProduct);
      editor.commit();
  }
  

• 如果要保存一系列产品.你做这个:

  private void addInJSONArray(Product productToAdd){
  
      Gson gson = new Gson();
      SharedPreferences sharedPref = getApplicationContext().getSharedPreferences(PREFS_TAG, Context.MODE_PRIVATE);
  
      String jsonSaved = sharedPref.getString(PRODUCT_TAG, "");
      String jsonNewproductToAdd = gson.toJson(productToAdd);
  
      JSONArray jsonArrayProduct= new JSONArray();
  
      try {
          if(jsonSaved.length()!=0){
              jsonArrayProduct = new JSONArray(jsonSaved);
          }
          jsonArrayProduct.put(new JSONObject(jsonNewproductToAdd));
      } catch (JSONException e) {
          e.printStackTrace();
      }
  
      //SAVE NEW ARRAY
      SharedPreferences.Editor editor = sharedPref.edit();
      editor.putString(PRODUCT_TAG, jsonArrayProduct);
      editor.commit();
  }
  

Answer 3

SharedPreferences mPrefs = getPreferences(MODE_PRIVATE);

为了保存

Editor prefsEditor = mPrefs.edit();
Gson gson = new Gson();
String json = gson.toJson(myObject);
prefsEditor.putString("MyObject", json);
prefsEditor.commit();

为了得到

Gson gson = new Gson();
String json = mPrefs.getString("MyObject", "");
MyObject obj = gson.fromJson(json, MyObject.class);

Answer 4

As said in accepted answer we can save list of objects like:

public <T> void setList(String key, List<T> list) {
        Gson gson = new Gson();
        String json = gson.toJson(list);
        set(key, json);
    }

    public void set(String key, String value) {
        if (setSharedPreferences != null) {
            SharedPreferences.Editor prefsEditor = setSharedPreferences.edit();
            prefsEditor.putString(key, value);
            prefsEditor.commit();
        }
    }

Get it by using:

public List<Company> getCompaniesList(String key) {
    if (setSharedPreferences != null) {

        Gson gson = new Gson();
        List<Company> companyList;

        String string = setSharedPreferences.getString(key, null);
        Type type = new TypeToken<List<Company>>() {
        }.getType();
        companyList = gson.fromJson(string, type);
        return companyList;
    }
    return null;
}