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.
Related
I want to replace cosmos batch with Stored Proc as my requirement is to upsert 100+ records which cosmos batch does not support. I am adding 2 java objects and 1 CosmosPatchOperations
in List and passing to below method.Whenver I am adding cosmos patch object no rows got inserted/updated otherwise it is working fine.I want to perform both insertion and patch operation in same transaction. Can somebody please guide how to modify SP so that it supports both insert and patch operation.
String rowsUpserted = "";
try
{
rowsUpserted = container
.getScripts()
.getStoredProcedure("createEvent")
.execute(Arrays.asList(listObj), options)
.getResponseAsString();
}catch(Exception e){
e.printStackTrace();
}
Stored Proc
function createEvent(items) {
var collection = getContext().getCollection();
var collectionLink = collection.getSelfLink();
var count = 0;
if (!items) throw new Error("The array is undefined or null.");
var numItems = items.length;
if (numItems == 0) {
getContext().getResponse().setBody(0);
return;
}
tryCreate(items[count], callback);
function tryCreate(item, callback) {
var options = { disableAutomaticIdGeneration: false };
var isAccepted = collection.upsertDocument(collectionLink, item, options, callback);
if (!isAccepted) getContext().getResponse().setBody(count);
}
function callback(err, item, options) {
if (err) throw err;
count++;
if (count >= numItems) {
getContext().getResponse().setBody(count);
} else {
tryCreate(items[count], callback);
}
}
}
Patching doesn't appear to be supported by the Collection type in the Javascript stored proc API. I suspect this was done as it's more an optimisiation for remote calls and SP execute locally so it's not really neccessary.
API reference is here: http://azure.github.io/azure-cosmosdb-js-server/Collection.html
upsertDocument is expecting the full document.
I'm implement an TextInputEditText with RxBinding.
Problem: When I do some math operation on first TextInputEditText and set the result to another TextInputEditText, The screen is not responding. When I start to type another digit, its not displayed in the edit text. I know why this happened, but don't know how to fix. For more detail, please check the code below.
Code:
class NumberSystemFragment : Fragment() {
override fun onCreateView() { ... }
override fun onViewCreated() {
binding?.run {
// It still ok if just observe a single edit text
etBinary.observeInput().subscribe {
val dec = it.fold(0L) { acc, el ->
(acc * 2) + el.digitToInt(radix = 2)
}
val oct = dec.toString(8)
val hex = dec.toString(16)
etDecimal.setText(dec.toString())
etOctal.setText(oct)
etHexadecimal.setText(hex)
}
// But, when I add more EditText, the screen will not responding.
// I know why this can happen, because when I set the result from operation above,
// and display it to another EditTexts, then the other EditText will begin to observe its input too.
// Then the racing condition or whatever it is, will occur.
etDecimal.observeInput().subscribe {
val bin = it.toLong().toString(2)
val oct = it.toLong().toString(8)
val hex = it.toLong().toString(16)
etBinary.setText(bin)
etOctal.setText(oct)
etHexadecimal.setText(hex)
}
}
}
private fun <T : EditText> T.observeInput() =
RxTextView.textChanges(this)
.skipInitialValue()
.subscribeOn(Schedulers.io())
.observeOn(AndroidSchedulers.mainThread())
.map(CharSequence::toString)
.publish()
.refCount()
}
Sorry, I'm new with RxJava, RxBinding, etc.
Two issues.
You have created a feedback loop by setting text on the other editors, which then trigger updates on the current editor.
If your code crashes, it will stop listening to values.
First of all, make these extension method changes:
private fun <T: EditText> T.observeInput() =
RxTextView.textChanges(this)
.skipInitialValue()
.map(CharSequence::toString) // <------------------ order matters
.distinctUntilChanged() // <----------------------- order matters
.observeOn(AndroidSchedulers.mainThread())
.publish()
.refCount()
private fun TextInputEditText.setText(text: CharSequence, onlyIfChanged: Boolean) {
if (onlyIfChanged) {
if (Objects.equals(this.text.toString(), text.toString())) {
return;
}
}
this.setText(text);
}
Then, update your onNext handlers:
// etBinary
// store calculation data
try {
Log.d("XYZ-etBinary", t);
val decResult = t.fold(0L) { acc, element ->
(acc * 2) + element.digitToInt(2)
}
val octResult = decResult.toString(8)
val hexResult = decResult.toString(16).uppercase()
// and display the results to another edit text which corresponds with their radix representation
etDecimal.setText(decResult.toString(), true)
etOctal.setText(octResult, true)
etHexadecimal.setText(hexResult, true)
} catch (e: Throwable) {
Log.e("XYZ-etBinary", e.message.toString())
}
// etDecimal
// store calculation data
try {
Log.d("XYZ-etDecimal", t);
val binResult = t.toLong().toString(2)
val octResult = t.toLong().toString(8)
val hexResult = t.toLong().toString(16).uppercase()
// and display the results to another edit text which corresponds with their radix representation
etBinary.setText(binResult, true)
etOctal.setText(octResult, true)
etHexadecimal.setText(hexResult, true)
} catch (e: Throwable) {
Log.e("XYZ-etDecimal", e.message.toString())
}
Also posted it as a Pull Request on your repo: https://github.com/dansampl/EditTextWithRxJavaSampleApp/pull/1/files
I have an AccountCreator class with a create method that takes a DTO with the data needed to create an account. At the beginning there is an attempt to create 2 value objects (UserName and Password), then validate the uniqueness of the user name, create the Account entity which takes these 2 value objects in the constructor and save it in the repo. Of course, errors such as incorrect password length, etc. may be returned. I used Eithers for this and now the question is whether this code is ok or maybe it can be written somehow better?
public Either<Error, AccountDto> create(AccountCreateDto accountCreateDto) {
var errorType = ErrorType.ACCOUNT_PERSISTENCE_ERROR;
var errorMessage = "Not unique user name: " + accountCreateDto.userName;
var error = new Error(errorType, errorMessage);
return UserName
.create(accountCreateDto.userName)
.flatMap(userName ->
userNameUniquenessChecker.isUnique(userName.text) ?
Password
.create(accountCreateDto.password)
.flatMap(password -> {
var createdAccount = new Account(
userName,
password,
AccountStatus.OPEN,
LocalDateTime.now(),
new ArrayList<>()
);
var addedAccount = accountRepository.add(createdAccount);
var accountDto = new AccountDto(
addedAccount.userName.text,
addedAccount.password.text,
addedAccount.status,
addedAccount.creationDate,
(long) addedAccount.tasks.size()
);
return Either.right(accountDto);
}) : Either.left(error));
}
The customary FP approach would be to use a Validation style applicative functor - there's one in Vavr called Validation. You can use Validation.combine to combine multiple Validation values into one, e.g.:
public Validation<Seq<<Error>, AccountDto> create(AccountCreateDto accountCreateDto) {
Validation<Seq<<Error>, Account> validAcc =
Validation.combine(
UserName.create(accountCreateDto.userName),
Password.create(accountCreateDto.password)
).ap((un, pw) -> new Account(
un,
pw,
AccountStatus.OPEN,
LocalDateTime.now()
);
Validation<Seq<<Error>, Account> validAcc2 =
validAcc.flatMap(acc -> validateUserIdIsUnique(acc));
Validation<<Seq<Error>, AccountDto> validAccDto =
validAcc2.map(accountRepository::add)
.map(addedAccount ->
new AccountDto(
addedAccount.userName.text,
addedAccount.password.text,
addedAccount.status,
addedAccount.creationDate,
(long) addedAccount.tasks.size()
)
);
}
return validAccDto;
}
private static final var errorType = ErrorType.ACCOUNT_PERSISTENCE_ERROR;
private static final var errorMessage = "Not unique user name: " + accountCreateDto.userName;
private static final var error = new Error(errorType, errorMessage);
Validation<Seq<Error>, Account> validateUserIdIsUnique(Account acc) {
return userNameUniquenessChecker.isUnique(acc.userName.text) ?
Validation.valid(userName) :
Validation.invalid(error);
}
You can elide the temporaries - validAcc, validAcc2 & validAccDto, however I left them in for clarity.
(caveat emptor - haven't tested that this code works, or even compiles)
I have a application which useds TFS JAVA SDK 14.0.3 .
I have a shared query on my tfs , how can i run the shared query and get the response back using TFS SDK 14.0.3
Also I could see that the query url will expire in every 90 days , so any better way to execute the shared query?
Now I have a method to run a query , i want method to run shared query also.
public void getWorkItem(TFSTeamProjectCollection tpc, Project project){
WorkItemClient workItemClient = project.getWorkItemClient();
// Define the WIQL query.
String wiqlQuery = "Select ID, Title,Assigned from WorkItems where (State = 'Active') order by Title";
// Run the query and get the results.
WorkItemCollection workItems = workItemClient.query(wiqlQuery);
System.out.println("Found " + workItems.size() + " work items.");
System.out.println();
// Write out the heading.
System.out.println("ID\tTitle");
// Output the first 20 results of the query, allowing the TFS SDK to
// page
// in data as required
final int maxToPrint = 5;
for (int i = 0; i < workItems.size(); i++) {
if (i >= maxToPrint) {
System.out.println("[...]");
break;
}
WorkItem workItem = workItems.getWorkItem(i);
System.out.println(workItem.getID() + "\t" + workItem.getTitle());
}
}
Shared query is a query which has been run and saved, so what you need should be getting a a shared query, not run a shared query. You could refer to case Access TFS Team Query from Client Object API:
///Handles nested query folders
private static Guid FindQuery(QueryFolder folder, string queryName)
{
foreach (var item in folder)
{
if (item.Name.Equals(queryName, StringComparison.InvariantCultureIgnoreCase))
{
return item.Id;
}
var itemFolder = item as QueryFolder;
if (itemFolder != null)
{
var result = FindQuery(itemFolder, queryName);
if (!result.Equals(Guid.Empty))
{
return result;
}
}
}
return Guid.Empty;
}
static void Main(string[] args)
{
var collectionUri = new Uri("http://TFS/tfs/DefaultCollection");
var server = new TfsTeamProjectCollection(collectionUri);
var workItemStore = server.GetService<WorkItemStore>();
var teamProject = workItemStore.Projects["TeamProjectName"];
var x = teamProject.QueryHierarchy;
var queryId = FindQuery(x, "QueryNameHere");
var queryDefinition = workItemStore.GetQueryDefinition(queryId);
var variables = new Dictionary<string, string>() {{"project", "TeamProjectName"}};
var result = workItemStore.Query(queryDefinition.QueryText,variables);
}
By the way, you could also check the REST API in the following link:
https://learn.microsoft.com/en-us/rest/api/vsts/wit/queries/get
I've got a list of futures that perform data deletion for given list of studentIds from cassandra:
val studentIds: List<String> = getStudentIds(...)
val boundStatements: List<BoundStatement> = studentIds.map(bindStudentDelete(it))
val deleteFutures = boundStatements.map { session.executeAsync(it) }
deleteFutures.forEach {
// callback that will send metrics for monitoring
Futures.addCallback(it, MyCallback(...))
}
Above I have registered a callback MyCallback(...) for each future for sending metrics. Then I do:
Futures.inCompletionOrder(deleteFutures).forEach { it.get() }
to wait for the completion of all the deletes. If for any reason that some of the futures end up failing (cancelled, something else goes wrong, etc.), I want to return the list of studentIds so that I can deal with it later.
What is the best way to achieve that?
EDIT
The callback could be a way to mutate a state to track success/failure of all the deletions.
class MyCallback(
private val statsDClient: StatsdClient,
private val tags: Array<String>,
val failures: MutableList<String>
) : FutureCallback<Any> {
override fun onSuccess(result: Any?) {
//send success metrics
...
}
override fun onFailure(t: Throwable) {
// send failure metrics
...
// do something here to get the associated studentId
val currId = ...
failures.add(currId)
}
}
Similarly, I could mutate a state in Futures.inCompletionOrder(deleteFutures).forEach block with a try/catch:
val failedDeletes = mutableListOf<String>()
Futures.inCompletionOrder(deleteFutures).forEach {
try {
it.get()
} catch (e: Exception) {
// do something to get the studentId for this future
val currId = ...
failedDeletes.add(currId)
}
}
However, there are 2 things I don't like/know about it. One is that it's mutating a state that we have to define outside. The other is that I still don't know how to get the studentId from the point of failure (in onFailure or catch block).
I have added a code snippet below in JAVA. This is blocking procedure.
ResultSet getUninterruptibly()
Waits for the query to return and return its result. This method is
usually more convenient than Future.get() because it:
Waits for the result uninterruptibly, and so doesn't throw InterruptedException.
Returns meaningful exceptions, instead of having to deal with ExecutionException.
As such, it is the preferred way to get the future result.
Check this link:
Interface ResultSetFuture
List<ResultSetFuture> futures = new ArrayList<>();
List<Long> futureStudentIds = new ArrayList<>();
// List<Long> successfullIds = new ArrayList<>();
List<Long> unsuccessfullIds = new ArrayList<>();
for (long studentid : studentids) {
futures.add(session.executeAsync(statement.deleteStudent(studentid)));
futureStudentIds.add(studentid);
}
for (int index = 0; index < futures.size(); index++) {
try {
futures.get(index).getUninterruptibly();
// successfullIds.add(futureStudentIds.get(index));
} catch (Exception e) {
unsuccessfullIds.add(futureStudentIds.get(index));
LOGGER.error("", e);
}
}
return unsuccessfullIds;
For Non-blocking you can use ListenableFuture.
Asynchronous queries with the Java driver