I have an ArrayList with custom objects. Each custom object contains a variety of strings and numbers. I need the array to stick around even if the user leaves the activity and then wants to come back at a later time, however I don't need the array available after the application has been closed completely. I save a lot of other objects this way by using the SharedPreferences but I can't figure out how to save my entire array this way. Is this possible? Maybe SharedPreferences isn't the way to go about this? Is there a simpler method?


当前回答

最好的方法是使用GSON转换为JSOn字符串并保存此字符串到SharedPreference。 我还使用这种方式缓存响应。

其他回答

    public  void saveUserName(Context con,String username)
    {
        try
        {
            usernameSharedPreferences= PreferenceManager.getDefaultSharedPreferences(con);
            usernameEditor = usernameSharedPreferences.edit();
            usernameEditor.putInt(PREFS_KEY_SIZE,(USERNAME.size()+1)); 
            int size=USERNAME.size();//USERNAME is arrayList
            usernameEditor.putString(PREFS_KEY_USERNAME+size,username);
            usernameEditor.commit();
        }
        catch(Exception e)
        {
            e.printStackTrace();
        }

    }
    public void loadUserName(Context con)
    {  
        try
        {
            usernameSharedPreferences= PreferenceManager.getDefaultSharedPreferences(con);
            size=usernameSharedPreferences.getInt(PREFS_KEY_SIZE,size);
            USERNAME.clear();
            for(int i=0;i<size;i++)
            { 
                String username1="";
                username1=usernameSharedPreferences.getString(PREFS_KEY_USERNAME+i,username1);
                USERNAME.add(username1);
            }
            usernameArrayAdapter = new ArrayAdapter<String>(this, android.R.layout.simple_dropdown_item_1line, USERNAME);
            username.setAdapter(usernameArrayAdapter);
            username.setThreshold(0);

        }
        catch(Exception e)
        {
            e.printStackTrace();
        }
    }

该方法用于存储/保存数组列表:-

 public static void saveSharedPreferencesLogList(Context context, List<String> collageList) {
            SharedPreferences mPrefs = context.getSharedPreferences("PhotoCollage", context.MODE_PRIVATE);
            SharedPreferences.Editor prefsEditor = mPrefs.edit();
            Gson gson = new Gson();
            String json = gson.toJson(collageList);
            prefsEditor.putString("myJson", json);
            prefsEditor.commit();
        }

该方法用于检索数组列表:-

public static List<String> loadSharedPreferencesLogList(Context context) {
        List<String> savedCollage = new ArrayList<String>();
        SharedPreferences mPrefs = context.getSharedPreferences("PhotoCollage", context.MODE_PRIVATE);
        Gson gson = new Gson();
        String json = mPrefs.getString("myJson", "");
        if (json.isEmpty()) {
            savedCollage = new ArrayList<String>();
        } else {
            Type type = new TypeToken<List<String>>() {
            }.getType();
            savedCollage = gson.fromJson(json, type);
        }

        return savedCollage;
    }

我使用相同的方式保存和检索字符串,但这里我使用HashSet作为数组列表的中介

使用HashSet保存arrayList到SharedPreferences:

1-我们创建SharedPreferences变量(在数组发生变化的地方)

2 -我们将数组列表转换为HashSet

3 -然后放入stringSet并应用

4 -你在HashSet中获取stringset并重新创建ArrayList来设置HashSet。

public class MainActivity extends AppCompatActivity {
    ArrayList<String> arrayList = new ArrayList<>();

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);

        SharedPreferences prefs = this.getSharedPreferences("com.example.nec.myapplication", Context.MODE_PRIVATE);

        HashSet<String> set = new HashSet(arrayList);
        prefs.edit().putStringSet("names", set).apply();


        set = (HashSet<String>) prefs.getStringSet("names", null);
        arrayList = new ArrayList(set);

        Log.i("array list", arrayList.toString());
    }
}

嘿,朋友们,我没有使用Gson库就得到了上述问题的解决方案。我在这里发布源代码。

1.变量声明,即

  SharedPreferences shared;
  ArrayList<String> arrPackage;

2.变量初始化,即

 shared = getSharedPreferences("App_settings", MODE_PRIVATE);
 // add values for your ArrayList any where...
 arrPackage = new ArrayList<>();

3.使用packagesharedPreferences()将值存储到sharedPreference:

 private void packagesharedPreferences() {
   SharedPreferences.Editor editor = shared.edit();
   Set<String> set = new HashSet<String>();
   set.addAll(arrPackage);
   editor.putStringSet("DATE_LIST", set);
   editor.apply();
   Log.d("storesharedPreferences",""+set);
 }

4.使用retriveSharedValue()检索sharedPreference的值:

 private void retriveSharedValue() {
   Set<String> set = shared.getStringSet("DATE_LIST", null);
   arrPackage.addAll(set);
   Log.d("retrivesharedPreferences",""+set);
 }

我希望这对你有帮助…

最好的方法是使用GSON转换为JSOn字符串并保存此字符串到SharedPreference。 我还使用这种方式缓存响应。