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
您可以将其转换为JSON字符串,并将字符串存储在SharedPreferences中。
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();
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());
}
}
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));
}
}
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