我已经使用如下简单的 Room 测试代码测试了一些测试用例。 “dao.getAll().observeForever()”在主要 Activity 恢复后不起作用。 正确插入新词,但仅观察不起作用。 如果我使用 dao.getAll().observe(),它总是能正常工作。 不允许在 Activity 的 onCreate() 方法上使用 observeForever?
应用数据库.java
@Database(entities = {Word.class}, version = 2)
public abstract class AppDatabase extends RoomDatabase {
private static AppDatabase sInstance;
public abstract WordDao wordDao();
public static AppDatabase getInstance(Context context) {
if (sInstance == null) {
synchronized (AppDatabase.class) {
if (sInstance == null) {
sInstance = Room.databaseBuilder(context.getApplicationContext(),
AppDatabase.class, "word.db").addMigrations(new Migration(1, 2) {
@Override
public void migrate(@NonNull SupportSQLiteDatabase database) {
}
}).build();
}
}
}
return sInstance;
}
Word.java
@Entity
public class Word {
@PrimaryKey(autoGenerate = true)
public int uid;
public String word;
public Word(String word) {
this.word = word;
}
WordDao.java
@Dao
public interface WordDao {
@Query("Select * from word")
LiveData<List<Word>> getAll();
@Update
void update(Word word);
@Insert
void insert(Word word);
主 Activity .java
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
TextView tv = findViewById(R.id.textview);
WordDao dao = AppDatabase.getInstance(this).wordDao();
dao.getAll().observeForever(wordlist -> {
StringBuilder builder = new StringBuilder();
for (Word w : wordlist ) {
builder.append(w.word).append(", ");
}
tv.setText(builder.toString());
});
findViewById(R.id.add).setOnClickListener(view -> new Thread(() -> {
dao.insert(new Word("haha"));
}).start());
}
构建.gradle
dependencies {
def lifecycle_version = "1.1.1"
implementation "android.arch.lifecycle:extensions:$lifecycle_version"
implementation "android.arch.lifecycle:common-java8:$lifecycle_version"
testImplementation "android.arch.core:core-testing:$lifecycle_version"
def room_version = "1.1.1"
implementation "android.arch.persistence.room:runtime:$room_version"
annotationProcessor "android.arch.persistence.room:compiler:$room_version"
testImplementation "android.arch.persistence.room:testing:$room_version"
}
最佳答案
永远不要使用那样的架构组件。您应该使用 MVVM,因为它们旨在解决这个问题。模型应包含您关于哪个房间可以使用的数据。然后你的 View 应该只包含演示和对第三个组件 View 模型的引用。您的代码中缺少 ViewModel,它是这样的:
public class WordViewModel extends ViewModel {
private MutableLiveData<List<Word>> mWords;
private AppDatabase mDb;
public WordViewModel(@NonNull Application application) {
super(application);
mWords = new MutableLiveData<List<Word>>();
mDb = AppDatabase.getInstance(application.getApplicationContext());
}
public LiveData<List<User>> getWords() {
loadWords();
return words;
}
private void loadWords() {
return mDb.wordDao().getAll();
}
}
然后你的Activity会变成
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
final TextView tv = findViewById(R.id.textview);
WordViewModel viewModel = ViewModelProviders.of(this).get(WordViewModel.class);
viewModel.getWords().observe(this, new Observer<List<Word>>() {
@Override
public void onChanged(@Nullable ResponseDataList resp) {
StringBuilder builder = new StringBuilder();
for (Word w : wordlist ) {
builder.append(w.word).append(", ");
}
tv.setText(builder.toString());
}
});
}
如果评论中有任何不清楚的地方,请告诉我
关于android - 房间 Livedata.observeforever 在 Activity 恢复后无法正常工作,我们在Stack Overflow上找到一个类似的问题: https://stackoverflow.com/questions/51027275/