我正在学习google的一个例子，这个例子在java但是当我用kotlin重写它时，我不能实例化这个类。我正在学习viewmodel。我很怀疑我是否搞砸了kotlin代码的语法。
https://github.com/googlecodelabs/android-room-with-a-view
// private lateinit var mWordViewModel: WordViewModel //not works
private var mWordViewModel: WordViewModel? = null //not works
private var wordListAdapter: WordListAdapter?= null
override fun onCreate(savedInstanceState: Bundle?) {
super.onCreate(savedInstanceState)
setContentView(R.layout.activity_main)
setSupportActionBar(toolbar)
try {
mWordViewModel = ViewModelProviders.of(this@MainActivity).get(WordViewModel::class.java)
}catch (e: Exception){
e.printStackTrace()
}
...
class WordViewModel(application: Application): AndroidViewModel(application) {
// super(application)
private var mRepository: WordRepository? = null
private var mAllWords: LiveData<List<Word>>? = null
init {
mRepository = WordRepository(application)
mAllWords = mRepository?.getAllWords()
}
...
class WordRepository(application: Application) {
private var mWordDao: WordDao? = null
private var mAllWords: LiveData<List<Word>>? = null
init {
val db = WordRoomDatabase.getDatabase(application)
mWordDao = db.wordDao()
mAllWords = mWordDao!!.getAlphabetizeWords()
}
...
@Database(entities = arrayOf(Word::class), version = 1)
abstract class WordRoomDatabase: RoomDatabase(){
abstract fun wordDao(): WordDao
companion object {
@JvmStatic
private var INSTANCE: WordRoomDatabase? = null
fun getDatabase(context: Context): WordRoomDatabase {
if (INSTANCE == null) {
synchronized(WordRoomDatabase::class.java) {
if (INSTANCE == null) {
INSTANCE = Room.databaseBuilder(context.applicationContext, WordRoomDatabase::class.java, "word_database")
.fallbackToDestructiveMigration()
.addCallback(sRoomDatabaseCallback)
.build()
}
}
}
return INSTANCE!!
}
@zunjae
错误
1-语法代码koltin。
2-项目配置。
class MainActivity: AppCompatActivity() {
mWordViewModel = ViewModelProviders.of(this@MainActivity).get(WordViewModel(application)::class.java)
...
class WordViewModel constructor (application: Application): AndroidViewModel(application){
...
class WordRepository constructor(application: Application) {
...
添加应用build. gradle
apply plugin: 'kotlin-kapt'
kapt "android.arch.lifecycle:extensions:$rootProject.archLifecycleVersion"
kapt "android.arch.persistence.room:compiler:$rootProject.roomVersion"
不过，我在JAVA中遇到了同样的问题。使用ViewModelFactory解决了我的问题，如下所示：
public class MyViewModelFactory implements ViewModelProvider.Factory {
private Application mApplication;
public MyViewModelFactory(Application application) {
mApplication = application;
}
@Override
public <T extends ViewModel> T create(Class<T> modelClass) {
return (T) new BookViewModel(mApplication);
}
在调用ViewModel的地方，将其更改为：
mBookViewModel = new ViewModelProvider(this, new MyViewModelFactory
(this.getApplication())).get(BookViewModel.class);
您可以从教程的Github问题页面查看此问题的链接：https://github.com/googlecodelabs/android-room-with-a-view/issues
