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
您还可以将数组列表转换为String并优先保存
private String convertToString(ArrayList<String> list) {
StringBuilder sb = new StringBuilder();
String delim = "";
for (String s : list)
{
sb.append(delim);
sb.append(s);;
delim = ",";
}
return sb.toString();
}
private ArrayList<String> convertToArray(String string) {
ArrayList<String> list = new ArrayList<String>(Arrays.asList(string.split(",")));
return list;
}
您可以使用convertToString方法将数组列表转换为字符串后保存它,并使用convertToArray方法检索字符串并将其转换为数组
在API 11之后,你可以直接保存设置到SharedPreferences !!:)
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。
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);
}
}
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() })
}
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();
}
}
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