Android 架构组件之Room数据库 处理Schema export Error

在使用 Android Room数据库的时候，虽然项目可以运行起来。

但是，却报以下error:

Error:(22, 17) 警告: Schema export directory is not provided to the annotation processor so we cannot export the schema.

You can either provide `room.schemaLocation` annotation processor argument OR set exportSchema to false.

实际上，上面已经提示了开发者应该怎么处理，给出了两种方案。

解决方式一：

给RoomDatabase设置exportSchema注解为false。

@Database(entities = { YourEntity.class }, version = 1, exportSchema = false)
public abstract class MovieDatabase extends RoomDatabase {

...

}

解决方案二：

在项目中gradle中通过 annotationProcessorOptions 注解，为

room.schemaLocation

指定schemas的子文件夹。

android {
compileSdkVersion 26
buildToolsVersion "26.0.2"
defaultConfig {
applicationId "com.xingen.architecturecomponents"
minSdkVersion 15
targetSdkVersion 26
versionCode 1
versionName "1.0"
testInstrumentationRunner "android.support.test.runner.AndroidJUnitRunner"

//指定room.schemaLocation生成的文件路径
javaCompileOptions {
annotationProcessorOptions {
arguments = ["room.schemaLocation": "$projectDir/schemas".toString()]
}
}
}

}

当执行项目后，在Android Studio 的Project视图下，查看项目，会发现Module生成了一个schemas的文件夹，如下图所示：



其中，会生成版本1的Json文件,这里可以查看Room数据库的配置情况：

{
"formatVersion": 1,
"database": {
"version": 1,
"identityHash": "8240057b6178b803a0bf9915edf969ef",
"entities": [
{
"tableName": "movies",
"createSql": "CREATE TABLE IF NOT EXISTS `${TABLE_NAME}` (`id` INTEGER PRIMARY KEY AUTOINCREMENT NOT NULL, `year` TEXT, `title` TEXT, `image` TEXT)",
"fields": [
{
"fieldPath": "id",
"columnName": "id",
"affinity": "INTEGER",
"notNull": true
},
{
"fieldPath": "year",
"columnName": "year",
"affinity": "TEXT",
"notNull": false
},
{
"fieldPath": "title",
"columnName": "title",
"affinity": "TEXT",
"notNull": false
},
{
"fieldPath": "image",
"columnName": "image",
"affinity": "TEXT",
"notNull": false
}
],
"primaryKey": {
"columnNames": [
"id"
],
"autoGenerate": true
},
"indices": [],
"foreignKeys": []
}
],
"setupQueries": [
"CREATE TABLE IF NOT EXISTS room_master_table (id INTEGER PRIMARY KEY,identity_hash TEXT)",
"INSERT OR REPLACE INTO room_master_table (id,identity_hash) VALUES(42, \"8240057b6178b803a0bf9915edf969ef\")"
]
}
}

以上项目案例的连接： https://github.com/13767004362/ArchitectureComponentsDemo

资源参考：

https://stackoverflow.com/questions/44322178/room-schema-export-directory-is-not-provided-to-the-annotation-processor-so-we