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[英]android room query method returning list but is wrongfully treated as LiveData
[英]Android Room query not returning the LiveData
我想從Android Room返回LiveData。 我將結果作為LiveData返回時遇到問題。
這是Dao
的摘錄
@Query("SELECT * FROM transaction_table")
LiveData<List<MyTransaction>> getAllTransactions();
@Query("SElECT * FROM transaction_table")
List<MyTransaction> getMyTransaction();
getAllTransactions()
調用在沒有異常的情況下運行,但不返回結果。 另一方面, getMyTransactions()
返回選擇查詢結果。
SDK Version: 23
Room Version: 2.1.0-beta01
編輯:
我在初始化時填充數據庫以進行測試。 這是代碼
private static class PopulateDbAsync extends AsyncTask<Void, Void, Void> {
private static final String TAG = "PopulateDbAsync";
private final TransactionDao mDao;
PopulateDbAsync(TransactionDatabase db) {
mDao = db.transactionDao();
}
@Override
protected Void doInBackground(Void... voids) {
mDao.deleteAll();
MyTransaction transaction = new MyTransaction();
transaction.setCardNumber("0123023403450456");
long result = mDao.insert(transaction);
Log.d(TAG, "doInBackground: " + String.format(Locale.US, "Result %d", result));
transaction = new MyTransaction();
transaction.setCardNumber("0123023403450457");
result = mDao.insert(transaction);
Log.d(TAG, "doInBackground: " + String.format(Locale.US, "Result %d", result));
LiveData<List<MyTransaction>> currentTransactions = mDao.getAllTransactions();
List<MyTransaction> txns = currentTransactions.getValue();
List<MyTransaction> transactions = mDao.getMyTransaction();
if(transactions != null) {
Log.d(TAG, "doInBackground: " + String.format(Locale.US, "Size = %d", transactions.size()));
}
return null;
}
}
如果不觀察LiveData,則無法檢索它。 這就是為什么以下代碼根本不起作用的原因。
LiveData<List<MyTransaction>> currentTransactions = mDao.getAllTransactions();
要使其工作首先觀察LiveData,然后監聽數據更改:
mDao.getAllTransactions().observe(this, new Observer<List<MyTransaction>>() {
@Override
public void onChanged(List<MyTransaction> myTransactionList) {
}
});
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