I'm managing my UI list with RealmRecyclerViewAdapter. I'd like to add a "pending" item to the collection that will display immediately while simultaneously posting the new item to the server. In case of failure, I will remove it from the display. Similar to a chat feature; I display the chat when they hit send, and if for some reason the post fails I can remove it and alert the user.
The problem is that with a regular RecyclerView adapter, I can just add one item to the end of the collection without an id, and remove it as needed. But since RealmRecyclerViewAdapter uses managed RealmResults, I can't add a new item without an id.
Can someone suggest a way to handle the situation I'm describing with RealmRecyclerViewAdapter?
Without knowing what your data model looks like. It is hard to give concrete advice, but it sounds like all your have ID's, so something like this should work:
1) It must be possible to generate ID's offline. The standard solution for that is GUIDs: https://en.wikipedia.org/wiki/Universally_unique_identifier
2) Have a boolean on your model class: "syncedWithServer" or something similar. Then you can render all items not yet synced as "pending".
public class ChatEntry extends RealmObject {
#PrimaryKey
private String id = UUID.randomUUID().toString();
private String entry;
private boolean syncedWithServer;
}
Related
I already have a list adapter that works properly. But I want to divide the object in the list into sections according to the date they were created. Something like this:
I found something called "sectioned recycler view" but couldn't find any documentation on that. I read all the related questions, but they all are either outdated or use a third-party library. What's the native way of implementing this feature?
There are a couple of approaches you could use. First the easy one:
make the header part of your item layout, but with GONE visibility by default
in onBindViewHolder, decide whether the header should be VISIBLE or GONE
The logic there depends on what you want, but it could be as simple as
val visible = position == 0 || items[position].date != items[position - 1].date
Basically you just need to work out what the condition is that would cause an item to be in a different "group" than the previous item, and then if it's met, show the header over that item.
The approach MarkL is talking about is more complex, but it's also more robust - by having separate Item and Header elements, you can treat them differently, and even do stuff like having the header collapse/show its children, select them all etc. You can do that with the other approach, but it requires more code since you're not really treating things as groups, it's more of a trick when it comes to displaying stuff.
Basically, ignoring the how for now, you need a list of headers and items. A sealed class is a good way to represent that:
sealed class ListElement {
data class Header(val date: Date) : ListElement()
data class Item(val itemData: YourItem) : ListElement()
}
I've made Item a wrapper class that holds your actual data object inside, since that's probably coming from elsewhere and you can't define it as part of this sealed class hierarchy - so sticking it inside one of the subclasses like this allows you to do that.
So now you can have a List<ListElement> containing Headers and Items in display order. Since you've mentioned creating the ViewHolders in a comment I won't explain all that, but basically when you're getting the item type for a position, you just need to check is Header or is Item and then handle it from there.
As for creating that list, there are lots of ways to do it - you could use groupBy to generate a Map of dates to lists of items, map each of those entries to a list of Header, Item, Item..., and flatten the whole thing into a single list:
items.map { Item(it) }
.groupBy { it.itemData.date }
.entries
.flatMap { (date, items) -> listOf(Header(date)) + items }
The advantage with a map like this is it's an actual grouped structure, so you can keep it around to generate flat lists for display - e.g. hiding a group's contents by only including the header in the list.
Or you could just build the list yourself, similar to the logic I mentioned in the first example - if the date has changed from the previous item, insert a Header first:
val list = mutableListOf<ListElement>().apply {
for (item in items) {
// add a header if the date changed - this handles the first header
// in an empty list too (where lastOrNull returns null, so the date is null)
val previousItemDate = (lastOrNull() as? Item)?.itemData?.date
if (previousItemDate != item.date) add(Header(item.date))
add(Item(item))
}
}
Or you could use fold. Don't forget to sort stuff!
You could create 2 types of view holders:
header which holds the date
data container which holds the other information.
And then create a list of objects which contain something like this:
listToBind = (header, data, data, header, data, data)
For your case, where header & info is the same object, you can do something like this:
take your object you receive from backend (example)
YourObject(val header: String, val info:InfoObject)
create 2 display objects, both inheriting from a type that your adapter accepts (say - AdapterDisplayEntity)
HeaderDisplayEntity(val header: String): AdapterDisplayEntity
InfoDisplayEntity(val info: InfoObject): AdapterDisplayEntity
now you can use your list that contains these items and submit to your adapter.
Use nested recycler view for this instead. You can check the example here.
Best solution for this scenario so far.
If you are using Jetpack Compose you can use the stickyHeader() as documented in the documentation
This question is about Couchbase lite (no Sync Gateway).
I'm new to Couchbase, I managed to use the demo app, but I don't understand it completely.
It contains this code which (as far as I understand, since I'm not native English speaker) retrieve views to populate a listview with the indexes:
// This code can be found in ListsActivity.java
// in the setupViewAndQuery() method
com.couchbase.lite.View listsView = mDatabase.getView("list/listsByName");
if (listsView.getMap() == null) {
listsView.setMap(new Mapper() {
#Override
public void map(Map<String, Object> document, Emitter emitter) {
String type = (String) document.get("type");
if ("task-list".equals(type)) {
emitter.emit(document.get("name"), null);
}
}
}, "1.0");
}
listsLiveQuery = listsView.createQuery().toLiveQuery();
Could anyone give me a hand with what each part is doing?
In which step is the listview populated
Can I change "list/listsByName" in the code (line 3)? What would happen?
Can I emit more than one element?
The code is a little bit convoluted. Let's answer the easy parts first.
Can I change "list/listsByName" in the code (line 3)?
Yes. That's just the name of the Couchbase View. You choose the View name. Unfortunately the terms used in Couchbase and Android overlap some. A Couchbase View is a kind of static index of your database.
Can I emit more than one element?
Yes. You can emit most anything you want. Take a look at the documentation here
Now, tracing how the Android ListView gets updated:
In ListsActivity.java notice in the onCreate method a ListAdapter instance gets added to the ListView. This ListAdapter is a private inner class that extends LiveQueryAdapter.
LiveQueryAdapter is in the utils subpackage. If you look at its constructor, you'll see it adds a change listener to the query passed in. When triggered, this change listener sets an enumerator equal to the rows passed back by the live query, then calls notifyDataSetChanged to tell the list to refresh itself. That, in turn, causes getView in ListAdapter to get called. That's where the data is pulled from the database and used to populate a list entry.
I'm new to Android programming, and still teaching myself to code.
Currently I'm teaching myself about GridViews and still coding that project with tutorials so I have nothing to show right now, but the basic idea is the following...
If I have images of groceries in GridView in the first activity and when you click an image you will be able to open a new activity with a larger image and you could input the number how many you things you need, like 5 apples or whatever.
All of that is more or less clear to me how to do.
But how would I send the number and image to a new (third) activity with a ListView that would list all the items you need to buy at the grocery store? How would I be able to fill the list only with items after you enter the number on the previous activity with the large picture and click an "OK" or "Add" button or whatever and not list absolutely everything?
Thanks!
It's difficult at first, but you can use an SQLiteDatabase to store the data.
It's not a quick solution for you, but definitely worth learning about if you're serious to learn android. Here's a link to the official stuff:
https://developer.android.com/reference/android/database/sqlite/SQLiteDatabase.html
I personally used this tutorial:
http://www.androidwarriors.com/2016/02/android-sqlite-database-tutorial-sqlite.html?m=1
Sharing some data between multiple activities or fragments is a very common situation. One way around it is implementing a Singleton Pattern.
In your case you can design some kind of data structure for your purpose and manage it inside shared singleton class. For example something like this:
public class ShoppingListManager {
private static ShoppingListManager instance = new ShoppingListManager();
private List<ShoppingItem> shoppingList;
public static ShoppingListManager getInstance() {
return instance;
}
public List<ShoppingItem> getShoppingList() {
return shoppingList;
}
public void addShoppingItem(ShoppingItem item) {
this.shoppingList.add(item);
}
...
// Make the constructor private so that this class cannot be instantiated
private ShoppingListManager(){
shoppingList = new ArrayList<String>();
}
}
Then you can access your data anywhere in your code and manage shared data in any way you'd like.
ShoppingListManager.getInstance().getShoppingList();
// You can add items in any activity
ShoppingListManager.getInstance().addShoppingItem(item);
One point to remember never store context in singleton classes as it will lead to memory leaks.
I have a class called Person one of the variables is a realm list called clothes:
public class Person extends RealmObject{
private RealmList<Clothing> clothes;
}
Clothes is used to display in a RecyclerView wherein the contents can be edited such as quantity, color of clothing, or cloth type.
When I edit the clothing values:
public void setCloth(int i, Cloth cloth) {
realmInstance.beginTransaction();
clothes.set(i, cloth);
realmInstance.commitTransaction();
}
Of course, the record is saved. My problem is what if the user, cancels the editing of the WHOLE Person object. Then the clothes list change will persist.
Please help.
I'm sure you would be a great fan of nested transactions (https://github.com/realm/realm-java/issues/1509).
In the next release of Realm, a new method copyFromRealm() will be introduced. You should copy the clothes list and use copyToRealmOrUpdate() when you commit the Person object.
I have now solved the issue:
The solution is if you're using a fragment or an activity, and displaying the realm object and it's relationship through widgets, begin transaction immediately.
Realm realmInstance = Realm.getInstance(this);
realmInstance.beginTransaction();
This way, changes done directly on the realm object whether a relationship or a plain variable will be allowed.
To cancel the changes done simply use:
realmInstance.cancelTransaction();
This code can be invoked by overriding onBackPressed or any means of canceling the editing.
After canceling the transaction, any changes done including the RealmList objects will be forfeited.
More Info:
I was displaying the clothes list array in a recyleview through an adapter with editing controls (etc. setting the qty, changing cloth type). This solution can also be used in that scenario.
Hope this helps.
Say I have a List<User>. Now I can wrap this list in an ArrayAdapter.
List<User> users = Users.getAll();
ArrayAdapter<User> = new ArrayAdapter<User>(this, android.R.layout.simple_list_item_1, users);
I then bind the adapter to a listview to display the list of Users.
Users.getAll() uses Sugar ORM to query the database and return a list of users. Items can be added to the user list from the activity that displays the user list. I am wondering how do I keep the listview updated.
Option 1
One way is to manually update the users as a I add to the database and then call adapter.notifyDataSetChanged(). This works, but it doesn't feel right because I am maintaining a "fake" list that represents what is in the database.
Option 2
I am wondering how bad is it if I just clear the items in users, update it with the results of a new database query and then call adapter.notifyDataSetChanged()?
Will all the child views be thrown away and be re-rendered? Or does it call the equals() method to see if the models bound to each child is the same and then update only what is new?
Other Info
Since I am using SugarORM, I don't think I can get access to the Cursor to do something more efficient. However if there is a better way to keep the list synced with SugarORM, I am happy to hear that as well.
In answer to your option 2: No, it doesnt call equals, because the adapter works in conjunction with the widget to re-use the views, it doens't create a new view foreach item in the list, it create a view foreach visible item and as you scroll re-uses view that left the screen.
The best option here is to create your own adapter, creating a class extending BaseAdapter and creating your own logic inside it requerying the database and notifying the change to the listview (or gridview)..
On the other hand doing what you said here:
I am wondering how bad is it if I just clear the items in users, update it with the results of a new database query and then call adapter.notifyDataSetChanged()?
isn't bad either.
Create a DAO class that extends Observable, then have your Adapter implement Observer. Now every time you add or remove a SugarRecord, do through the DAO class and whoever is register as the Observer will get notified through the following method:
#Override
public void update(Observable observable, Object o)
You can more about Observable/Observer pattern here. This is just one of the many examples and tutorials out there.