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

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));
    }

}

其他回答

对于String, int, boolean,最好的选择是sharedPreferences。

如果你想存储数组列表或任何复杂的数据。最好的选择是Paper library。

添加依赖关系

implementation 'io.paperdb:paperdb:2.6'

初始化文件

应该在Application.onCreate()中初始化一次:

Paper.init(context);

Save

List<Person> contacts = ...
Paper.book().write("contacts", contacts);

加载数据

如果对象在存储中不存在,请使用默认值。

List<Person> contacts = Paper.book().read("contacts", new ArrayList<>());

给你。

https://github.com/pilgr/Paper

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。

您可以将其转换为Map Object来存储它,然后在检索SharedPreferences时将值更改回ArrayList。

下面的代码是公认的答案,为新手(我)多写几行,例如。说明了如何将set类型对象转换回arrayList,并提供了关于`之前操作的附加指导。putStringSet'和。getstringset '。(谢谢你邪恶)

// shared preferences
   private SharedPreferences preferences;
   private SharedPreferences.Editor nsuserdefaults;

// setup persistent data
        preferences = this.getSharedPreferences("MyPreferences", MainActivity.MODE_PRIVATE);
        nsuserdefaults = preferences.edit();

        arrayOfMemberUrlsUserIsFollowing = new ArrayList<String>();
        //Retrieve followers from sharedPreferences
        Set<String> set = preferences.getStringSet("following", null);

        if (set == null) {
            // lazy instantiate array
            arrayOfMemberUrlsUserIsFollowing = new ArrayList<String>();
        } else {
            // there is data from previous run
            arrayOfMemberUrlsUserIsFollowing = new ArrayList<>(set);
        }

// convert arraylist to set, and save arrayOfMemberUrlsUserIsFollowing to nsuserdefaults
                Set<String> set = new HashSet<String>();
                set.addAll(arrayOfMemberUrlsUserIsFollowing);
                nsuserdefaults.putStringSet("following", set);
                nsuserdefaults.commit();

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());
    }
}