我可以使用以下代码从主应用程序活动中打开数据库,但是一旦将其包装到一个单例对象中,它就会不断抛出空对象错误:
object CommonClass {
fun openSQLDatabase(): SQLiteDatabase? {
var dbase: SQLiteDatabase? = null
try {
dbase = openOrCreateDatabase(
"dbfile.sqlite",
Context.MODE_PRIVATE, null
)
} catch (e: SQLException) {
println(e.message)
}
return dbase
}
}
我假设主AppCompatActivity应该以某种方式将其上下文传递给该对象,但是我无法找到有效的模型。
to Swayangjit
Android Studio突出显示Context.MODE_PRIVATE参数并将其标记为:
Type mismatch.
Required: SQLiteDatabase.CursorFactory?
Found: Int
但是当我将AppCompatActivity实现到单例对象并从主活动传递Context.MODE_PRIVATE时,它会运行,但会引发此错误:
java.lang.NullPointerException: Attempt to invoke virtual method 'android.database.sqlite.SQLiteDatabase android.content.Context.openOrCreateDatabase(java.lang.String, int, android.database.sqlite.SQLiteDatabase$CursorFactory)' on a null object reference
我相信以下内容会起作用:-
object CommonClass {
fun openSQLDatabase(context: Context): SQLiteDatabase? {
var dbase: SQLiteDatabase? = null
if (dbase == null) {
try {
dbase = openOrCreateDatabase(context.getDatabasePath("dbfile.sqlite"), null)
} catch (e: SQLException) {
println(e.message)
}
}
return dbase
}
}
data/data/the_package_name/databases/dbfile.sqlite
您可以使用类似:-]的方法来调用/调用它
val mydb = CommonClass.openSQLDatabase(this)