我正在android中开发一个电子商务应用程序，我必须在其中创建多个表，在其上插入数据并从该表中获取活动/片段中的数据（在Spinner中加载值，基于运行条件的子查询等）。为此，我宣布了2张桌子。地址，银行如下
bank.Java
@Entity
public class Bank {
@PrimaryKey(autoGenerate = true)
public int id;
public String bankId;
public String bankName;
public String bankType;
public Bank() {
}
public String getBankId() {
return bankId;
}
public String getBankName() {
return bankName;
}
public String getBankType() {
return bankType;
}
}
address.Java
@Entity
public class Address {
@PrimaryKey(autoGenerate = true)
public int id;
public String state;
public String district;
public String block;
public String id_panchayat;
public String panchayat;
public Address() {
}
public String getState() {
return state;
}
public String getDistrict() {
return district;
}
public String getBlock() {
return block;
}
public String getId_panchayat() {
return id_panchayat;
}
public String getPanchayat() {
return panchayat;
}
}
这两个表的Dao类是：
bank DAO.Java
@Dao
public interface BankDao {
@Insert(onConflict = REPLACE)
void insertSingleBank (Bank bank);
@Insert(onConflict = REPLACE)
void insertMultipleBank (List<Bank> bankList);
@Query("SELECT * FROM Bank")
LiveData<List<Bank>> getAllBank();
@Query("SELECT bankName FROM Bank")
List<String> getAllBankData ();
@Query("SELECT * FROM Bank WHERE bankName = :bankName")
Bank getBankSubData (String bankName);
@Query("DELETE FROM Bank")
void deleteBank();
}
address DAO.Java
@Dao
public interface AddressDao {
@Insert(onConflict = REPLACE)
void insertSingleAddress(Address address);
@Insert(onConflict = REPLACE)
void insertMultipleAddress(List<Address> addressList);
@Query("SELECT * FROM Address")
LiveData<List<Address>> getAllAddress();
@Query("SELECT state FROM Address")
List<String> getAllStateList();
@Query("SELECT district FROM Address WHERE state = :state")
List<String> getDistrictListAll(String state);
@Query("SELECT block FROM Address WHERE state = :state AND district = :district")
List<String> getBlockListAll(String state, String district);
@Query("SELECT panchayat FROM Address WHERE state = :state AND district = :district AND block = :block")
List<String> getPanchayatListAll(String state, String district, String block);
@Query("DELETE FROM Address")
void deleteAddress();
}
而这两个类的ViewModel是
address model.Java
public class AddressModel extends AndroidViewModel {
private RoomDatabaseHelper roomDatabase;
private final LiveData<List<Address>> getAllAddress;
public AddressModel(Application application) {
super(application);
roomDatabase = RoomDatabaseHelper.getInstance(this.getApplication());
getAllAddress = roomDatabase.daoAddress().getAllAddress();
}
public void insertSingleAddress(Address address) {
new InsertSingleAddressAsyncTask(roomDatabase).execute(address);
}
private static class InsertSingleAddressAsyncTask extends AsyncTask<Address, Void, Void> {
private RoomDatabaseHelper db;
InsertSingleAddressAsyncTask(RoomDatabaseHelper userDatabase) {
db = userDatabase;
}
@Override
protected Void doInBackground(Address...params) {
db.daoAddress().insertSingleAddress(params[0]);
return null;
}
}
public void insertMultipleAddress(List<Address> registrationList) {
new InsertMultipleAddressAsyncTask(roomDatabase).execute(registrationList);
}
private static class InsertMultipleAddressAsyncTask extends AsyncTask<List<Address>, Void, Void> {
private RoomDatabaseHelper db;
InsertMultipleAddressAsyncTask(RoomDatabaseHelper userDatabase) {
db = userDatabase;
}
@Override
protected Void doInBackground(List<Address>...params) {
db.daoAddress().insertMultipleAddress(params[0]);
return null;
}
}
public LiveData<List<Address>> getAllAddress() {
return getAllAddress;
}
}
bank model.Java
public class BankModel extends AndroidViewModel {
private RoomDatabaseHelper roomDatabase;
private final LiveData<List<Bank>> getAllBank;
public BankModel(Application application) {
super(application);
roomDatabase = RoomDatabaseHelper.getInstance(this.getApplication());
getAllBank = roomDatabase.daoBank().getAllBank();
}
public void insertSingleBank(Bank bank) {
new InsertSingleBankAsyncTask(roomDatabase).execute(bank);
}
private static class InsertSingleBankAsyncTask extends AsyncTask<Bank, Void, Void> {
private RoomDatabaseHelper db;
InsertSingleBankAsyncTask(RoomDatabaseHelper userDatabase) {
db = userDatabase;
}
@Override
protected Void doInBackground(Bank...params) {
db.daoBank().insertSingleBank(params[0]);
return null;
}
}
public void insertMultipleBank(List<Bank> registrationList) {
new InsertMultipleBankAsyncTask(roomDatabase).execute(registrationList);
}
private static class InsertMultipleBankAsyncTask extends AsyncTask<List<Bank>, Void, Void> {
private RoomDatabaseHelper db;
InsertMultipleBankAsyncTask(RoomDatabaseHelper userDatabase) {
db = userDatabase;
}
@Override
protected Void doInBackground(List<Bank>...params) {
db.daoBank().insertMultipleBank(params[0]);
return null;
}
}
public LiveData<List<Bank>> getAllBank() {
return getAllBank;
}
}
RoomDatabase类是
room database helper.Java
@Database(entities = {Address.class, Bank.class}, version = 1, exportSchema = false)
public abstract class RoomDatabaseHelper extends RoomDatabase {
private static RoomDatabaseHelper sInstance;
public static synchronized RoomDatabaseHelper getInstance(Context context) {
if (sInstance == null) {
sInstance = Room.databaseBuilder(context.getApplicationContext(), RoomDatabaseHelper.class, "DemoTable").build();
}
return sInstance;
}
public abstract AddressDao daoAddress();
public abstract BankDao daoBank();
}
在我的片段中：
BankModel bankModel = ViewModelProviders.of(this).get(BankModel.class);
AddressModel addressModel = ViewModelProviders.of(this).get(AddressModel.class);
现在根据文档从两个Model类访问getAllBank()和getAllAddress()我必须像这样定义
addressModel.getAllAddress().observe(mActivity, new Observer<List<Address>>() {
@Override
public void onChanged(List<Address> addressList) {
}
});
addressModel.getAllBank().observe(mActivity, new Observer<List<Bank>>() {
@Override
public void onChanged(final List<Bank> bankList) {
}
});
现在这两种方法都是AsyncTask之类的东西。所以在活动负载上，我无法改变与UI相关的事情。我必须将整个用户界面放在onChange下。我怎样才能同时访问两个观察者。导致嵌套观察者不是正确的解决方案。而且我还需要许多复杂的数据库查询。因此，我必须定义这么多的观察者，或者还有其他任何解决方案。
首先，ViewModels应该用作片段或活动的帮助程序，以检索和处理视图所需的数据。因此，一个Activity / Fragment应该有一个viewmodel。在这里，您将它们用作某种存储库。
如果你还想那样使用它们：How can I access both observer at the same
在onChanged上调用像tryUpdateUi()这样的方法，你检查getAllBank().getValue()和getAllAddress().getValue()是否都不为空。如果是这样，您可以进行更新/计算等。
虽然我更喜欢在ViewModel中进行此检查和数据处理，但使用另一个LiveData将处理后的模型传递给Fragment。它可以通过MediatorLiveData，docs来实现