java - 房间类型转换器不工作

Question

我遇到 Room 无法识别我的转换器的问题。错误:

Cannot figure out how to save this field into database. You can consider adding a type converter for it.  

我需要在数据库中存储一些 map 和集合。我究竟做错了什么？ room 不喜欢接口(interface)或泛型吗？
代码:(抱歉所有字段和类名，它们是英语和捷克语的混合体，与某些 java 类名称不同):
转换器(仅部分)

public class MyConverter {
/**
 * makes a string like 1;2;3;5;4;8;1;6;8;4 from a collection of integers.
 */
@TypeConverter
public static @NonNull String toString(@NonNull Collection<Integer> c) {
    StringBuilder sb = new StringBuilder();
    for (Integer item : c) {
        sb.append(item.toString() + ";");
    }
    sb.delete(sb.length()-1,sb.length()-1);
    return sb.toString();
}

/**
 * makes a Set<Integer> from string like 1;2;3;4;5;6
 * @throws NumberFormatException on incorrect input
 */
@TypeConverter
public static@NonNull  Set<Integer> toIntegerSet(@NonNull String s) {
    Set<Integer> set = new LinkedHashSet<>();
    String[] split = s.split(";");
    try {
        for (String item : split) {
            set.add(Integer.parseInt(item));
        }
    }catch (NumberFormatException e){
        throw new NumberFormatException("Could not make set of integers (like 1;2;3;8;7) from \"" + s +"\"");
    }
    return set;
}
}  

数据库:

@Database(entities = {SQLUkol.class,SQLPredmet.class,SQLList.class},version = 1)
@TypeConverters({MyConverter.class})
public abstract class AppDatabase extends RoomDatabase {
    public abstract MojeDAO mojeDao();
}  

实体之一(不包括 getter、setter 和构造函数):

    @Entity(primaryKeys = {"id", "list_id"},
        indices = {@Index("list_id")},
        foreignKeys = @ForeignKey(entity = SQLList.class, parentColumns = "id", 
childColumns = "list_id", onDelete = ForeignKey.CASCADE),
        tableName = "ukols")
public class SQLUkol implements Comparable<SQLUkol> {
    @ColumnInfo(name = "list_id")
    private final int listID;
    private final int id;
    private String title;
    @ColumnInfo(name = "title_changed")
    private boolean titleChanged = false;
    private String notes;
    @ColumnInfo(name = "notes_changed")
    private boolean notesChanged = false;
    private boolean completed;
    @ColumnInfo(name = "completed_changed")
    private boolean completedChanged = false;
    private LocalDate date;
    @ColumnInfo(name = "date_changed")
    private boolean dateChanged = false;
    @Embedded
    private final SQLData data;
}

Answer 1

Room 不太喜欢泛型。我必须这样做:

@TypeConverter
public static String toString1(Map<String, String> m){
    ...
}

@TypeConverter
public static String toString2(Map<Integer, String> m){
    ...
}

@TypeConverter
public static String toString3(Set<Integer> s){
    ...
}

@TypeConverter
public static String toString4(List<Integer> l){
    ...
}

不只是

@TypeConverter
public static String toString(Map m){
    ...
}

@TypeConverter
public static String toString(Collection<Integer> c){
    ...
}