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

正如@nirav所说,最好的解决方案是使用Gson实用工具类将其作为json文本存储在sharedpreferences中。下面是示例代码:

//Retrieve the values
Gson gson = new Gson();
String jsonText = Prefs.getString("key", null);
String[] text = gson.fromJson(jsonText, String[].class);  //EDIT: gso to gson


//Set the values
Gson gson = new Gson();
List<String> textList = new ArrayList<String>(data);
String jsonText = gson.toJson(textList);
prefsEditor.putString("key", jsonText);
prefsEditor.apply();

其他回答

为什么不把数组列表放在应用程序类上呢?它只有在应用被杀死时才会被销毁,所以,只要应用可用,它就会一直存在。

我已经阅读了上面所有的答案。这都是正确的,但我找到了一个更简单的解决方案如下:

Saving String List in shared-preference>> public static void setSharedPreferenceStringList(Context pContext, String pKey, List<String> pData) { SharedPreferences.Editor editor = pContext.getSharedPreferences(Constants.APP_PREFS, Activity.MODE_PRIVATE).edit(); editor.putInt(pKey + "size", pData.size()); editor.commit(); for (int i = 0; i < pData.size(); i++) { SharedPreferences.Editor editor1 = pContext.getSharedPreferences(Constants.APP_PREFS, Activity.MODE_PRIVATE).edit(); editor1.putString(pKey + i, (pData.get(i))); editor1.commit(); } } and for getting String List from Shared-preference>> public static List<String> getSharedPreferenceStringList(Context pContext, String pKey) { int size = pContext.getSharedPreferences(Constants.APP_PREFS, Activity.MODE_PRIVATE).getInt(pKey + "size", 0); List<String> list = new ArrayList<>(); for (int i = 0; i < size; i++) { list.add(pContext.getSharedPreferences(Constants.APP_PREFS, Activity.MODE_PRIVATE).getString(pKey + i, "")); } return list; }

这里的常数。APP_PREFS是要打开的文件的名称;不能包含路径分隔符。

这应该可以工作:

public void setSections (Context c,  List<Section> sectionList){
    this.sectionList = sectionList;

    Type sectionListType = new TypeToken<ArrayList<Section>>(){}.getType();
    String sectionListString = new Gson().toJson(sectionList,sectionListType);

    SharedPreferences.Editor editor = getSharedPreferences(c).edit().putString(PREFS_KEY_SECTIONS, sectionListString);
    editor.apply();
}

他们,要抓住它才:

public List<Section> getSections(Context c){

    if(this.sectionList == null){
        String sSections = getSharedPreferences(c).getString(PREFS_KEY_SECTIONS, null);

        if(sSections == null){
            return new ArrayList<>();
        }

        Type sectionListType = new TypeToken<ArrayList<Section>>(){}.getType();
        try {

            this.sectionList = new Gson().fromJson(sSections, sectionListType);

            if(this.sectionList == null){
                return new ArrayList<>();
            }
        }catch (JsonSyntaxException ex){

            return new ArrayList<>();

        }catch (JsonParseException exc){

            return new ArrayList<>();
        }
    }
    return this.sectionList;
}

这对我很管用。

在SharedPreferences中保存数组:

public static boolean saveArray()
{
    SharedPreferences sp = PreferenceManager.getDefaultSharedPreferences(this);
    SharedPreferences.Editor mEdit1 = sp.edit();
    /* sKey is an array */
    mEdit1.putInt("Status_size", sKey.size());  

    for(int i=0;i<sKey.size();i++)  
    {
        mEdit1.remove("Status_" + i);
        mEdit1.putString("Status_" + i, sKey.get(i));  
    }

    return mEdit1.commit();     
}

从SharedPreferences加载数组数据

public static void loadArray(Context mContext)
{  
    SharedPreferences mSharedPreference1 =   PreferenceManager.getDefaultSharedPreferences(mContext);
    sKey.clear();
    int size = mSharedPreference1.getInt("Status_size", 0);  

    for(int i=0;i<size;i++) 
    {
     sKey.add(mSharedPreference1.getString("Status_" + i, null));
    }

}

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());
    }
}