///缓存管理类
class HiCache {
SharedPreferences? prefs;

HiCache._() {
init();
}

static HiCache? _instance;

HiCache._pre(SharedPreferences prefs) {
this.prefs = prefs;
}

///预初始化，防止在使用get时，prefs还未完成初始化
static Future preInit() async {
if (_instance == null) {
var prefs = await SharedPreferences.getInstance();
_instance = HiCache._pre(prefs);//这里没有返回任何东西 为何能对_instance赋值 不是null吗
}
return _instance!;
}

static HiCache getInstance() {
if (_instance == null) {
instance = HiCache.();
}
return _instance!;
}

void init() async {
if (prefs == null) {
prefs = await SharedPreferences.getInstance();
}
}

setString(String key, String value) {
prefs?.setString(key, value);
}

setDouble(String key, double value) {
prefs?.setDouble(key, value);
}

setInt(String key, int value) {
prefs?.setInt(key, value);
}

setBool(String key, bool value) {
prefs?.setBool(key, value);
}

setStringList(String key, List value) {
prefs?.setStringList(key, value);
}

remove(String key) {
prefs?.remove(key);
}

T? get(String key) {
var result = prefs?.get(key);
if (result != null) {
return result as T;
}
return null;
}
}