Java POJO Object
public class Section {
@ColumnInfo(name="section_id")
public int mSectionId;
@ColumnInfo(name="section_name")
public String mSectionName;
public int getSectionId() {
return mSectionId;
}
public void setSectionId(int mSectionId) {
this.mSectionId = mSectionId;
}
public String getSectionName() {
return mSectionName;
}
public void setSectionName(String mSectionName) {
this.mSectionName = mSectionName;
}
}
My Query method
@Query("SELECT * FROM section")
LiveData<List<Section>> getAllSections();
Accessing DB
final LiveData<List<Section>> sections = mDb.sectionDAO().getAllSections();
On the next line I am checking sections.getValue()
which is always giving me null although I have data in the DataBase and later I am getting the value in the onChanged()
method.
sections.observe(this, new Observer<List<Section>>() {
@Override
public void onChanged(@Nullable List<Section> sections){
}
});
But when I omit LiveData from the query I am getting the data as expected. Query Method:
@Query("SELECT * FROM section")
List<Section> getAllSections();
Accessing DB:
final List<Section> sections = mDb.sectionDAO().getAllSections();
I solve this problem through this approach
private MediatorLiveData<List<Section>> mSectionLive = new MediatorLiveData<>();
.
.
.
@Override
public LiveData<List<Section>> getAllSections() {
final LiveData<List<Section>> sections = mDb.sectionDAO().getAllSections();
mSectionLive.addSource(sections, new Observer<List<Section>>() {
@Override
public void onChanged(@Nullable List<Section> sectionList) {
if(sectionList == null || sectionList.isEmpty()) {
// Fetch data from API
}else{
mSectionLive.removeSource(sections);
mSectionLive.setValue(sectionList);
}
}
});
return mSectionLive;
}