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
嘿,朋友们,我没有使用Gson库就得到了上述问题的解决方案。我在这里发布源代码。
1.变量声明,即
SharedPreferences shared;
ArrayList<String> arrPackage;
2.变量初始化,即
shared = getSharedPreferences("App_settings", MODE_PRIVATE);
// add values for your ArrayList any where...
arrPackage = new ArrayList<>();
3.使用packagesharedPreferences()将值存储到sharedPreference:
private void packagesharedPreferences() {
SharedPreferences.Editor editor = shared.edit();
Set<String> set = new HashSet<String>();
set.addAll(arrPackage);
editor.putStringSet("DATE_LIST", set);
editor.apply();
Log.d("storesharedPreferences",""+set);
}
4.使用retriveSharedValue()检索sharedPreference的值:
private void retriveSharedValue() {
Set<String> set = shared.getStringSet("DATE_LIST", null);
arrPackage.addAll(set);
Log.d("retrivesharedPreferences",""+set);
}
我希望这对你有帮助…
其他回答
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();
}
}
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。
使用Kotlin,对于简单的数组和列表,你可以这样做:
class MyPrefs(context: Context) {
val prefs = context.getSharedPreferences("x.y.z.PREFS_FILENAME", 0)
var listOfFloats: List<Float>
get() = prefs.getString("listOfFloats", "").split(",").map { it.toFloat() }
set(value) = prefs.edit().putString("listOfFloats", value.joinToString(",")).apply()
}
然后轻松访问首选项:
MyPrefs(context).listOfFloats = ....
val list = MyPrefs(context).listOfFloats
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();
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。
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