我刚开始在我当前的Android应用程序中使用Realm，到目前为止它很棒。 不幸的是我遇到了一个问题：
在我的应用程序中，用户可以添加不同类型的条目（他今天吃了什么？他有什么饮料？等等）到他的日记中。 一个DiaryEntry对象表示给定日期所有条目的总和（例如，21.05.2017等）。
public class DiaryEntry extends RealmObject {
// ID of the day this diary entry represents
@PrimaryKey private Integer dateId;
private RealmList<MealEntry> mealEntries;
private RealmList<DrinkEntry> drinkEntries;
private RealmList<SymptomEntry> symptomEntries;
private RealmList<MedicineEntry> medicineEntries;
public void addMealEntry(MealEntry mealEntry) {
mealEntries.add(mealEntry);
}
public RealmList<MealEntry> getMealEntries() {
return mealEntries;
}
public void addDrinkEntry(DrinkEntry drinkEntry) {
drinkEntries.add(drinkEntry);
}
public RealmList<DrinkEntry> getDrinkEntries() {
return drinkEntries;
}
public void addSymptomEntry(SymptomEntry symptomEntry) {
symptomEntries.add(symptomEntry);
}
public RealmList<SymptomEntry> getSymptomEntries() {
return symptomEntries;
}
public void addMedicineEntry(MedicineEntry medicineEntry) {
medicineEntries.add(medicineEntry);
}
public RealmList<MedicineEntry> getMedicineEntries() {
return medicineEntries;
}
}
要在日记中显示特定日期的此数据，应按用户创建条目的时间对所有条目进行排序。 因此，每个条目对象都包含一个字段'time'。
private int time;
我想出了一个解决我问题的临时解决方案，但这远非完美。 以下代码在UI线程上执行，这显然是不好的做法。
List<RealmObject> entryList = new ArrayList<>();
OrderedRealmCollectionSnapshot<MealEntry> mealEntries = diaryEntry.getMealEntries().createSnapshot();
OrderedRealmCollectionSnapshot<DrinkEntry> drinkEntries = diaryEntry.getDrinkEntries().createSnapshot();
OrderedRealmCollectionSnapshot<MedicineEntry> medicineEntries = diaryEntry.getMedicineEntries().createSnapshot();
OrderedRealmCollectionSnapshot<SymptomEntry> symptomEntries = diaryEntry.getSymptomEntries().createSnapshot();
entryList.addAll(mealEntries);
entryList.addAll(drinkEntries);
entryList.addAll(medicineEntries);
entryList.addAll(symptomEntries);
Collections.sort(entryList, entryComparator);
对条目列表进行排序的代码通过调用time字段的getter方法来使用反射：
public int compare(RealmObject entry1, RealmObject entry2) {
try {
Method timeGetter1 = entry1.getClass().getMethod("getTime");
Method timeGetter2 = entry2.getClass().getMethod("getTime");
int time1 = (Integer) timeGetter1.invoke(entry1);
int time2 = (Integer) timeGetter2.invoke(entry2);
return time1 - time2;
} catch (NoSuchMethodException e) {
e.printStackTrace();
Timber.d("No such method 'getTime'.");
}
// Other catch clauses
正如我之前所说，所有这些都发生在UI线程上。
我知道我无法通过线程传递RealmObject s，RealmList和RealmResult，因此我真的很难为此提出异步解决方案。我想到了一个后台线程，并在那里创建RealmList对象内所有DiaryEntry的副本。然后合并这个非托管列表并对其进行排序 - 所有这些都在后台线程中。
所以我的问题：是否有任何首选策略可以合并多个RealmList并对合并列表进行排序 - 所有这些都是以异步方式进行的？我上面描述的尝试会起作用吗？
答案 0 :(得分：1)
谢谢@EpicPandaForce
我完全按照你所描述的方式解决了它，它就像一个魅力 - 现在我甚至拥有实时功能，无需手动刷新数据，很好：）
如果有人遇到同样的问题，我会在这里发布一些代码片段，说明我是如何在代码中解决的。
public class Entry extends RealmObject {
private static final int ENTRY_MEAL = 0;
private static final int ENTRY_DRINK = 1;
private static final int ENTRY_SYMPTOM = 2;
private static final int ENTRY_MEDICINE = 3;
/** The tag describes what kind of entry it represents */
private int tag;
/* Only one of these can be set, according to what this entry represents. */
@Nullable private MealEntry mealEntry;
@Nullable private DrinkEntry drinkEntry;
@Nullable private SymptomEntry symptomEntry;
@Nullable private MedicineEntry medicineEntry;
/** The time value this entry was created at */
/** Format: hours + minutes * 60 */
private int time;
public int getTime() {
return time;
}
/* Can only be accessed from within the 'data' package */
void setTime(int time) {
this.time = time;
}
/**
* Creates a new entry object in the realm database and tags it as 'MEAL'
*
* @param realm not null
* @param mealEntry the {@link MealEntry} object to map this entry to, not null
*
* @return the newly created entry
*/
static Entry createEntryAsMeal(@NonNull final Realm realm, @NonNull final MealEntry mealEntry) {
if(realm == null) {
throw new IllegalArgumentException("'realm' may not be null");
}
if(mealEntry == null) {
throw new IllegalArgumentException("'mealEntry' may not be null");
}
Entry entry = realm.createObject(Entry.class);
entry.tag = ENTRY_MEAL;
entry.mealEntry = mealEntry;
return entry;
}
/* Same methods for other tag types ... */
在MealEntry.class中：
public class MealEntry extends RealmObject {
@PrimaryKey @Required private String id;
@Required private String title;
/** The entry objects this meal-entry is added to */
Entry entry;
/** This time value describes when the user consumed this meal **/
private int time;
// other fields
/**
* Creates a new MealEntry object in the realm.
* <p>
* Note: It is important to use this factory method for creating {@link MealEntry} objects in realm.
* Under the hood, a {@link Entry} object is created for every MealEntry and linked to it.
* </p>
*
* @param realm not null
*
* @return new MealEntry object which has been added to the <code>realm</code>
*/
public static MealEntry createInRealm(@NonNull Realm realm) {
if(realm == null) {
throw new IllegalArgumentException("'realm' may not be null");
}
MealEntry mealEntry = realm.createObject(MealEntry.class, UUID.randomUUID().toString());
mealEntry.entry = Entry.createEntryAsMeal(realm, mealEntry);
return mealEntry;
}
“时间”字段存在于Entry.class和MealEntry.class中，因此如果后者更改，则必须相应地更新条目：
/**
* Sets the time value for the <code>mealEntry</code> to the specified value.
* <p>
* Note: This method is necessary in order to sync the new time value with the underlying
* {@link Entry} object that is connected with the <code>mealEntry</code>.
* </p>
*
* @param mealEntry the {@link MealEntry} object to set the time for, not null
*
* @param time the new time value, must be in range of [0, 24*60] because of the format: hours*60 + minutes
*
*/
public static void setTimeForMealEntry(@NonNull MealEntry mealEntry, @IntRange(from=0, to=24*60) int time) {
if(mealEntry == null) {
throw new IllegalArgumentException("'mealEntry' may not be null");
}
mealEntry.setTime(time);
Entry entry = mealEntry.entry;
if(entry == null) {
throw new IllegalStateException("'mealEntry' contains no object of type 'Entry'! Something went wrong on creation of the 'mealEntry'");
}
/* Syncs the entries time value with the time value for this MealEntry. */
/* That´s important for sorting a list of all entries. */
entry.setTime(time);
}
注意：我只能在MealEntry中存储相应Entry对象的ID，反之亦然，Entry对象将ID存储到相应的MealEntry对象。但是，我不知道这样做的性能有何不同，所以我采用了上述方法。 另一种方法的一个原因是我不必将'time'字段存储两次，一次存入Entry.class，一次存放在MealEntry.class中，因为在Entry.class中我可以得到时间通过ID找到相应的MealEntry对象，然后获取时间。