Android Room TypeConverters无法识别

Question

我正在努力实现一个DateConverter持久的日期.它非常通用,但我一直得到:

无法弄清楚如何将此字段保存到数据库中.您可以考虑为其添加类型转换器.

我仔细检查并在数据库级别和字段级别定义了注释,它仍然无法解决为字段定义的类型转换器.

我的成绩文件依赖项:

compile('android.arch.persistence.room:runtime:1.0.0-alpha3') {
    exclude group: 'com.google.code.gson'
}
compile('android.arch.persistence.room:rxjava2:1.0.0-alpha3') {
    exclude group: 'com.google.code.gson'
}
testCompile('android.arch.persistence.room:testing:1.0.0-alpha3') {
    exclude group: 'com.google.code.gson'
}
annotationProcessor('android.arch.persistence.room:compiler:1.0.0-alpha3') {
    exclude group: 'com.google.code.gson'
}

在我的AppDatabase中:

@Database(entities = {Location.class, Room.class, Amenity.class, UserModel.class, EventModel.class}, version =1, exportSchema = false)
@TypeConverters({DateConverter.class})
public abstract class AppDatabase extends RoomDatabase {

    public abstract RoomDao getRoomDao();
    public abstract LocationDao getLocationDao();
    public abstract AmenityDao getAmenityDao();
    public abstract UserDao getUserDao();
    public abstract EventDao getEventDao();

}

然后我的DateConverter班级看起来像这样:

public class DateConverter {

    @TypeConverter
    public static Date toDate(Long timestamp) {
        return timestamp == null ? null : new Date(timestamp);
    }

    @TypeConverter
    public static long toTimestamp(Date date) {
        return date == null ? null : date.getTime();
    }
}

我的实体看起来像这样:

@Entity(tableName = "event")
@TypeConverters({DateConverter.class})
public class EventModel {

    @PrimaryKey
    private String uuid;

    @ColumnInfo(name = "subject")
    private String subject;

    @TypeConverters({DateConverter.class})
    private Date start;

    @TypeConverters({DateConverter.class})
    private Date end;

    @ColumnInfo(name = "confirmed")
    private Boolean confirmed;

    public String getUuid() {return uuid;}
    public void setUuid(String uuid) {this.uuid = uuid;}

    public String getSubject() {return subject;}
    public void setSubject(String subject) {
        this.subject = subject;
    }

    public Date getStart() {return start;}
    public void setStart(Date date) {this.start = date;}

    public Date getEnd() {return end;}
    public void setEnd (Date end) {
        this.end = end;

    }

    public Boolean getConfirmed() {return confirmed;}

    public void setConfirmed(Boolean confirmed) {
        this.confirmed = confirmed;
    }

}

我还遗失了什么吗？谢谢!

Answer 1

尝试改变：

public static long toTimestamp(Date date)

到：

public static Long toTimestamp(Date date)

或者，将另一个人的参数更改为long。IOW，让他们使用相同的类型。

例如，在这个示例项目中，我使用了以下类，它工作正常：

/***
 Copyright (c) 2017 CommonsWare, LLC
 Licensed under the Apache License, Version 2.0 (the "License"); you may not
 use this file except in compliance with the License. You may obtain    a copy
 of the License at http://www.apache.org/licenses/LICENSE-2.0. Unless required
 by applicable law or agreed to in writing, software distributed under the
 License is distributed on an "AS IS" BASIS,    WITHOUT WARRANTIES OR CONDITIONS
 OF ANY KIND, either express or implied. See the License for the specific
 language governing permissions and limitations under the License.

 Covered in detail in the book _Android's Architecture Components_
 https://commonsware.com/AndroidArch
 */

package com.commonsware.android.room;

import android.arch.persistence.room.TypeConverter;
import java.util.Date;

public class TypeTransmogrifier {
  @TypeConverter
  public static Long fromDate(Date date) {
    if (date==null) {
      return(null);
    }

    return(date.getTime());
  }

  @TypeConverter
  public static Date toDate(Long millisSinceEpoch) {
    if (millisSinceEpoch==null) {
      return(null);
    }

    return(new Date(millisSinceEpoch));
  }
}

Answer 2

Kotlin中的等效项是：（至少我正在使用的那个）

class DateConverter {
    @TypeConverter
    fun toDate(timestamp: Long?): Date? {
        return when (timestamp) {
            null -> null
            else -> Date(timestamp)
        }
    }

    @TypeConverter
    fun toTimestamp(date: Date?): Long? {
        return date?.time
    }
}

然后，您将拥有数据库：

@Database(entities = arrayOf(MyObject::class), version = 1)
@TypeConverters(DateConverter::class)
abstract class MyObjectDb : RoomDatabase() {
    abstract fun myObjectDao(): MyObjectDao
}