I am following this tutorial by Raywenderlich on paging-library-for-android-with-kotlin on how to use android paging library. This is one of the easiest tutorials on the net and I have followed it thoroughly. However, I would like to make some changes so that I can intelligently switch between online data and offline data.
That is, I have old some posts in my database. Initially I have internet connection. So I load latest data from internet, then insert it into my database. Finally, I show this latest data in my recyclerView / PagedListAdapter.
If for some reason, there is no internet connection after sometime, I should show the old posts from database.
How can I do this?
My attempts:
This is my code on github repository.
Here, I tried to create a factory pattern. It checks if initially I have internet, the factory returns pagedList from online dataSource. ELse, the factory returns pagedList from offline dataSource.
But this doesnot intelligently switch between the 2 states.
I tried some random codes such as creating a boundary callback. But I am not sure how to make the necessary changes.
I am not adding codes here (at least for now) to keep it short and precise.
Can anyone help me?
Edit:
To be specific, I am loading paged data primarily from network. If there is a network error, I don't want to show the user an error. Instead I load paged data from cache / database and continuously show it to my user as long as possible. If the network is back,switch back to network paged data. (that's what instagram / facebook does I think). What is the appropriate way to implement this? See my code / attemp in the answer.
Okay, so after trying out some codes for 2 days, this is what I came up with. However, I really don't know if this is a good pratice or not. So I am open to any acceptable answers.
Explanation:
Since I have multiple data sources(network and database), I created ProfilePostDataSource: PageKeyedDataSource<Pair<Long, Long>, ProfilePost> here the key is a pair, the 1st one for network pagination, the 2nd one is for database pagination.
I used kotlin's Coroutine to write some asynchronous codes in a simple if-else like manner. So we can write it in a psudo-code like this:
Database db;
Retrofit retrofit;
inside loadInitial/loadBefore / loadAfter:
currNetworkKey = params.key.first;
currDBKey = params.key.second;
ArrayList<Model> pagedList;
coroutine{
ArrayList<Model> onlineList = retrofit.getNetworkData(currNetworkKey); // <-- we primarily load data from network
if(onlineList != null) {
pagedList = onlineList;
db.insertAll(onlineList); // <-- update our cache
}else{
ArrayList<Model> offlineList = db.getOfflineData(currDBKey); // <-- incase the network fails, we load cache from database
if(offlineList !=null){
pagedList = offlineList;
}
}
if(pagedList != null or empty) {
nextNetworkKey = // update it accordingly
nextDBKey = // update it accordingly
Pair<int, int> nextKey = new Pair(nextNetworkKey, nextDBKey);
pagingLibraryCallBack.onResult(pagedList, nextKey); // <-- submit the data to paging library via callback. this updates your adapter, recyclerview etc...
}
}
So in apps like facebook, instagram etc, we see them primarily loading data from network. But if the network is down, they show you a cashed data. We can intelligently make this switch like this code.
Here is a relevant code snippet, the PageKeyedDataSource written in kotlin:
ProfilePostDataSource.kt
/** #brief: <Key, Value> = <Integer, ProfilePost>. The key = pageKey used in api. Value = single item data type in the recyclerView
*
* We have a situation. We need a 2nd id to fetch profilePosts from database.
* Change of plan: <Key, Value> = < Pair<Int, Int>, ProfilePost>. here the
*
* key.first = pageKey used in api. <-- Warning: Dont switch these 2!
* Key.second = db last items id
* used as out db page key
*
* Value = single item data type in the recyclerView
*
* */
class ProfilePostDataSource: PageKeyedDataSource<Pair<Long, Long>, ProfilePost> {
companion object{
val TAG: String = ProfilePostDataSource::class.java.simpleName;
val INVALID_KEY: Long = -1;
}
private val context: Context;
private val userId: Int;
private val liveLoaderState: MutableLiveData<NetworkState>;
private val profilePostLocalData: ProfilePostLocalDataProvider;
public constructor(context: Context, userId: Int, profilePostLocalData: ProfilePostLocalDataProvider, liveLoaderState: MutableLiveData<NetworkState>) {
this.context = context;
this.userId = userId;
this.profilePostLocalData = profilePostLocalData;
this.liveLoaderState = liveLoaderState;
}
override fun loadInitial(params: LoadInitialParams<Pair<Long, Long>>, pagingLibraryCallBack: LoadInitialCallback<Pair<Long, Long>, ProfilePost>) {
val initialNetworkKey: Long = 1L; // suffix = networkKey cz later we'll add dbKey
var nextNetworkKey = initialNetworkKey + 1;
val prevNetworkKey = null; // cz we wont be using it in this case
val initialDbKey: Long = Long.MAX_VALUE; // dont think I need it
var nextDBKey: Long = 0L;
GlobalScope.launch(Dispatchers.IO) {
val pagedProfilePosts: ArrayList<ProfilePost> = ArrayList(); // cz kotlin emptyList() sometimes gives a weird error. So use arraylist and be happy
val authorization : String = AuthManager.getInstance(context).authenticationToken;
try{
setLoading();
val res: Response<ProfileServerResponse> = getAPIService().getFeedProfile(
sessionToken = authorization, id = userId, withProfile = false, withPosts = true, page = initialNetworkKey.toInt()
);
if(res.isSuccessful && res.body()!=null) {
pagedProfilePosts.addAll(res.body()!!.posts);
}
}catch (x: Exception) {
Log.e(TAG, "Exception -> "+x.message);
}
if(pagedProfilePosts.isNotEmpty()) {
// this means network call is successfull
Log.e(TAG, "key -> "+initialNetworkKey+" size -> "+pagedProfilePosts.size+" "+pagedProfilePosts.toString());
nextDBKey = pagedProfilePosts.last().id;
val nextKey: Pair<Long, Long> = Pair(nextNetworkKey, nextDBKey);
pagingLibraryCallBack.onResult(pagedProfilePosts, prevNetworkKey, nextKey);
// <-- this is paging library's callback to a pipeline that updates data which inturn updates the recyclerView. There is a line: adapter.submitPost(list) in FeedProfileFragment. this callback is related to that line...
profilePostLocalData.insertProfilePosts(pagedProfilePosts, userId); // insert the latest data in db
}else{
// fetch data from cache
val cachedList: List<ProfilePost> = profilePostLocalData.getProfilePosts(userId);
pagedProfilePosts.addAll(cachedList);
if(pagedProfilePosts.size>0) {
nextDBKey = cachedList.last().id;
}else{
nextDBKey = INVALID_KEY;
}
nextNetworkKey = INVALID_KEY; // <-- probably there is a network error / sth like that. So no need to execute further network call. thus pass invalid key
val nextKey: Pair<Long, Long> = Pair(nextNetworkKey, nextDBKey);
pagingLibraryCallBack.onResult(pagedProfilePosts, prevNetworkKey, nextKey);
}
setLoaded();
}
}
override fun loadBefore(params: LoadParams<Pair<Long, Long>>, pagingLibraryCallBack: LoadCallback<Pair<Long, Long>, ProfilePost>) {} // we dont need it in feedProflie
override fun loadAfter(params: LoadParams<Pair<Long, Long>>, pagingLibraryCallBack: LoadCallback<Pair<Long, Long>, ProfilePost>) {
val currentNetworkKey: Long = params.key.first;
var nextNetworkKey = currentNetworkKey; // assuming invalid key
if(nextNetworkKey!= INVALID_KEY) {
nextNetworkKey = currentNetworkKey + 1;
}
val currentDBKey: Long = params.key.second;
var nextDBKey: Long = 0;
if(currentDBKey!= INVALID_KEY || currentNetworkKey!= INVALID_KEY) {
GlobalScope.launch(Dispatchers.IO) {
val pagedProfilePosts: ArrayList<ProfilePost> = ArrayList(); // cz kotlin emptyList() sometimes gives a weird error. So use arraylist and be happy
val authorization : String = AuthManager.getInstance(context).authenticationToken;
try{
setLoading();
if(currentNetworkKey!= INVALID_KEY) {
val res: Response<ProfileServerResponse> = getAPIService().getFeedProfile(
sessionToken = authorization, id = userId, withProfile = false, withPosts = true, page = currentNetworkKey.toInt()
);
if(res.isSuccessful && res.body()!=null) {
pagedProfilePosts.addAll(res.body()!!.posts);
}
}
}catch (x: Exception) {
Log.e(TAG, "Exception -> "+x.message);
}
if(pagedProfilePosts.isNotEmpty()) {
// this means network call is successfull
Log.e(TAG, "key -> "+currentNetworkKey+" size -> "+pagedProfilePosts.size+" "+pagedProfilePosts.toString());
nextDBKey = pagedProfilePosts.last().id;
val nextKey: Pair<Long, Long> = Pair(nextNetworkKey, nextDBKey);
pagingLibraryCallBack.onResult(pagedProfilePosts, nextKey);
setLoaded();
// <-- this is paging library's callback to a pipeline that updates data which inturn updates the recyclerView. There is a line: adapter.submitPost(list) in FeedProfileFragment. this callback is related to that line...
profilePostLocalData.insertProfilePosts(pagedProfilePosts, userId); // insert the latest data in db
}else{
// fetch data from cache
// val cachedList: List<ProfilePost> = profilePostLocalData.getProfilePosts(userId);
val cachedList: List<ProfilePost> = profilePostLocalData.getPagedProfilePosts(userId, nextDBKey, 20);
pagedProfilePosts.addAll(cachedList);
if(pagedProfilePosts.size>0) {
nextDBKey = cachedList.last().id;
}else{
nextDBKey = INVALID_KEY;
}
nextNetworkKey = INVALID_KEY; // <-- probably there is a network error / sth like that. So no need to execute further network call. thus pass invalid key
val nextKey: Pair<Long, Long> = Pair(nextNetworkKey, nextDBKey);
pagingLibraryCallBack.onResult(pagedProfilePosts, nextKey);
setLoaded();
}
}
}
}
private suspend fun setLoading() {
withContext(Dispatchers.Main) {
liveLoaderState.value = NetworkState.LOADING;
}
}
private suspend fun setLoaded() {
withContext(Dispatchers.Main) {
liveLoaderState.value = NetworkState.LOADED;
}
}
}
Thank you for reading this far. If you have a better solution, feel free to let me know. I'm open to any working solutions.
Some background:
I have a map where I allow the user to click and select a place. Then I am getting the address from the place where they clicked.
What I want to do: Using that address, which is a String, I want to get details about that place by using the new Google Map Places API.
I'm attempting to do this with the code below
//Make the Autocomplete request builder with the String address
FindAutocompletePredictionsRequest.Builder requestBuilder =
FindAutocompletePredictionsRequest.builder()
.setQuery(address)
.setTypeFilter(TypeFilter.ADDRESS);
placesClient = Places.createClient(getApplicationContext());
//Create the Autocomplete Task
Task<FindAutocompletePredictionsResponse> task =
placesClient.findAutocompletePredictions(requestBuilder.build());
task.addOnSuccessListener(new OnSuccessListener<FindAutocompletePredictionsResponse>() {
#Override
public void onSuccess(final FindAutocompletePredictionsResponse findAutocompletePredictionsResponse) {
//Use the response to get a list of Predictions
List<AutocompletePrediction> list = findAutocompletePredictionsResponse.getAutocompletePredictions();
if (list.isEmpty() || list == null) {
} else {
//Get the first Autocomplete prediction and later, it's ID.
AutocompletePrediction ap = list.get(0);
//Provide a list of Place Fields that I want to retrieve.
List<Place.Field> placeFields = Arrays.asList(Place.Field.ID, Place.Field.NAME, Place.Field.ADDRESS);
//Make the request to fetch the place using the Place ID obtained from the Autocomplete prediction.
FetchPlaceRequest request = FetchPlaceRequest.builder(ap.getPlaceId(), placeFields).build();
placesClient = Places.createClient(getApplicationContext());
//Using the Place ID from the Autocomplete prediction, make a request to fetch places.
placesClient.fetchPlace(request).addOnSuccessListener(new OnSuccessListener<FetchPlaceResponse>() {
#Override
public void onSuccess(FetchPlaceResponse fetchPlaceResponse) {
//Use the response to get the Place Object
Place place = fetchPlaceResponse.getPlace();
//Display the results from the Place Object
displayResults("\n-----------------\nName: " + place.getName() + "\nAddress: " + place.getAddress());
}
}).addOnFailureListener(new OnFailureListener() {
//......
});
}
}
});
task.addOnFailureListener(new OnFailureListener() {
//......
});
Problem: The problem is that when I do this and use place.getName(), instead of displaying the location's name, as it should, it displays the first part of the address like the street number and name. Additionally, other Fields like the phone number and opening hours are null.
Does anybody know how I can get the Place Object from the String address?
Getting details about the place where the user clicks is the most important feature of my Android app.
I am using the new Places API since the Place Details and Place Picker are now deprecated.
before voting down please read my question , which I have searched a lot but I couldn't find the answer yet, so I would appreciate if you give me hand to overcome the problem.
Actually I need to update a tuple in a table named "Demographics". But it seems my code does not work correctly, and in fact after running the app , I got the result "0" for updating which means nothing get updated.
12-21 12:34:54.190 2351-2367/? D/Update Result:: =0
I guess my problem is due to not pointing to the right row of the table based on Primary key. Actually when a user Register to my app the following things should happen:
1- Create a tuple in "Demographics" table --> username, password and email will be inserted. An auto increment primary key also constructed and inserted.
2- user logins , then he can complete rest of information in "Demographics" table. --> this MODIFICATION is the "update" process which I', asking.
Would you please tell me if the following codes are wrong or have any implicit error?
DemographicsCRUD.java
public long UpdateDemographics(Demographics_to demoId) {
//SQLiteDatabase db = dbHelper.getWritableDatabase();
ContentValues values = new ContentValues();
values.put(DataBaseHelper.lastName, demoId.getD_lastName());
values.put(DataBaseHelper.firstName, demoId.getD_firstName());
values.put(DataBaseHelper.dateOfBirth, demoId.getD_dateOfBirth())
long result = database.update(dbHelper.Demographics_Table, values,
WHERE_ID_EQUALS,
new String[]{String.valueOf(demoId.getD_patientID())});
Log.d("Update Result:", "=" + result);
// db.close();
return result;
}
here is where I call the above code:
private void updateDemographicsTable()
{
ep_demoId = new Demographics_to();
String ep_na = ep_name.getText().toString();
String ep_fa = ep_family.getText().toString();
.
.
.
ep_demoId.setD_dateOfBirth(ep_bd);
ep_demoId.setD_firstName(ep_na);
ep_demoId.setD_lastName(ep_fa);
}
#Override
protected Long doInBackground(Void... arg0) {
long result = ep_demoCRUD.UpdateDemographics(ep_demoId);
return result;
}
#Override
protected void onPostExecute(Long result) {
if (activityWeakRef.get() != null
&& !activityWeakRef.get().isFinishing()) {
if (result != -1)
Toast.makeText(activityWeakRef.get(), "Information Updated!",
Toast.LENGTH_LONG).show();
}}
Looks like whatever you are passing in as the patientID does not have a matching record in the database or the dataobject "Demographics_to" has the patient ID set incorrectly.
I need to batch elements that have similar client id (String type, but at the moment only numeric values, like "12345", "235134", etc.)
Map<String, List<Client>> _batched = new HashMap<String, List<Client>>();
for (Client c : _Clients)
{
String id = c.getIdClient();
List<Client> clients = _batched.get(id);
if(_clients == null){
clients = new ArrayList<Client>();
_batched.put(id, clients);
}
clients.add(c);
}
The problem is that when I compare this function with the results of Excel (=SUM(IF(FREQUENCY(C2:C618,C2:C618)>0,1))), then I get different results, i.e. 526 and 519.
Is something wrong with my code?
Your problem is here:
String id = c.getIdClient();
List<Client> _clients = _batched.get(id);
if(_clients == null){
pois = new ArrayList<Client>();
_batched.put(id, _clients);
}
_clients.add(c);
You create a new array into a variable called pois but then put the contents of the variable _clients into _batched. What happens with the value put into pois?
I don't understand how that doesn't null pointer exception actually.
I can't seem to update an existing record in my table using a strongly-typed dataset. I can add a new record, but if I make changes to an existing record it doesn't work.
Here is my code:
private void AddEmplMaster()
{
dsEmplMast dsEmpMst = new dsEmplMast();
SqlConnection cn = new SqlConnection();
cn.ConnectionString = System.Configuration.ConfigurationSettings.AppSettings["cn.ConnectionString"];
SqlDataAdapter da1 = new SqlDataAdapter("SELECT * FROM UPR00100", cn);
SqlCommandBuilder cb1 = new SqlCommandBuilder(da1);
da1.Fill(dsEmpMst.UPR00100);
DataTable dtMst = UpdateEmpMst(dsEmpMst);
da1.Update(dsEmpMst.UPR00100);
}
This procedure is called from above to assign the changed fields to a record:
private DataTable UpdateEmpMst(dsEmplMast dsEmpMst)
{
DataTable dtMst = new DataTable();
try
{
dsEmplMast.UPR00100Row empRow = dsEmpMst.UPR00100.NewUPR00100Row();
empRow.EMPLOYID = txtEmplId.Text.Trim();
empRow.LASTNAME = txtLastName.Text.Trim();
empRow.FRSTNAME = txtFirstName.Text.Trim();
empRow.MIDLNAME = txtMidName.Text.Trim();
empRow.ADRSCODE = "PRIMARY";
empRow.SOCSCNUM = txtSSN.Text.Trim();
empRow.DEPRTMNT = ddlDept.SelectedValue.Trim();
empRow.JOBTITLE = txtJobTitle.Text.Trim();
empRow.STRTDATE = DateTime.Today;
empRow.EMPLOYMENTTYPE = "1";
dsEmpMst.UPR00100.Rows.Add(empRow);
}
catch { }
return dtMst;
}
Thank you
UPDATE:
Ok I figured it out. In my UpdateEmpMst() procedure I had to check if the record exists then to retrieve it first. If not then create a new record to add. Here is what I added:
try
{
dsEmplMast.UPR00100Row empRow;
empRow = dsEmpMst.UPR00100.FindByEMPLOYID(txtEmplId.Text.Trim());
if (empRow == null)
{
empRow = dsEmpMst.UPR00100.NewUPR00100Row();
dsEmpMst.UPR00100.Rows.Add(empRow);
}
then I assign my data to the new empRow I created and updates fine.
In order to edit an existing record in a dataset, you need to access a particular column of data in a particular row. The data in both typed and untyped datasets can be accessed via the following:
With the indices of the tables, rows, and columns collections.
By passing the table and column names as strings to their respective collections.
Although typed datasets can use the same syntax as untyped datasets, there are additional advantages to using typed datasets. For more information, see the "To update existing records using typed datasets" section below.
To update existing records in either typed or untyped datasets
Assign a value to a specific column within a DataRow object.
The table and column names of untyped datasets are not available at design time and must be accessed through their respective indices.