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
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。
其他回答
还有Kotlin:
fun SharedPreferences.Editor.putIntegerArrayList(key: String, list: ArrayList<Int>?): SharedPreferences.Editor {
putString(key, list?.joinToString(",") ?: "")
return this
}
fun SharedPreferences.getIntegerArrayList(key: String, defValue: ArrayList<Int>?): ArrayList<Int>? {
val value = getString(key, null)
if (value.isNullOrBlank())
return defValue
return ArrayList (value.split(",").map { it.toInt() })
}
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();
以防有人需要保存列表的列表,即list < list < String > >。我是这样做的:
序列化
Gson gson = new Gson();
// Save the size of the array
sharedPreferencesEditor.putInt("ArraySize", myArray.size());
for (int i=0; i<myArray.size(); i++) {
String key = "Array"+i;
String json = gson.toJson(myArray.get(i));
sharedPreferencesEditor.putString(key, json);
}
sharedPreferencesEditor.commit();
反序列化
// Get the size of the array to be deserialized. In my case, the default number should be 3
int arraySize = sharedPreferences.getInt("ArraySize",3);
myArray = new ArrayList<List<String>>();
for (int i=0; i<arraySize; i++) {
String key = "Array"+i;
String json = sharedPreferences.getString(key, null);
List<String> arrayTemp= gson.fromJson(json, List.class);
myArray.add(arrayTemp);
}
// My array may also include components with empty strings.
// Gson makes them null values and it is not possible
// to deserialize them as empty strings.
// The following takes care of that:
for (int i=0; i<myArray.size();i++) {
if (myArray.get(i) == null) {
List<String> emptyComponent = new ArrayList<String>() {
{ add(""); }
};
myArray.set(i,emptyComponent);
}
}
您可以将其转换为JSON字符串,并将字符串存储在SharedPreferences中。
你可以使用Gson库保存字符串和自定义数组列表。
首先你需要创建一个函数来保存数组列表到SharedPreferences。
public void saveListInLocal(ArrayList<String> list, String key) {
SharedPreferences prefs = getSharedPreferences("AppName", Context.MODE_PRIVATE);
SharedPreferences.Editor editor = prefs.edit();
Gson gson = new Gson();
String json = gson.toJson(list);
editor.putString(key, json);
editor.apply(); // This line is IMPORTANT !!!
}
你需要创建一个函数来从SharedPreferences获取数组列表。
public ArrayList<String> getListFromLocal(String key)
{
SharedPreferences prefs = getSharedPreferences("AppName", Context.MODE_PRIVATE);
Gson gson = new Gson();
String json = prefs.getString(key, null);
Type type = new TypeToken<ArrayList<String>>() {}.getType();
return gson.fromJson(json, type);
}
如何调用保存和检索数组列表函数。
ArrayList<String> listSave=new ArrayList<>();
listSave.add("test1"));
listSave.add("test2"));
saveListInLocal(listSave,"key");
Log.e("saveArrayList:","Save ArrayList success");
ArrayList<String> listGet=new ArrayList<>();
listGet=getListFromLocal("key");
Log.e("getArrayList:","Get ArrayList size"+listGet.size());
不要忘记在你的应用级别build.gradle中添加gson库。
实现“com.google.code.gson: gson: 2.8.2”
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