I have stored in shared_preferences key value pairs like below....
item_001 = 'some data'
item_103 = 'some data'
item_007 = 'some data'
item_059 = 'some data'
I am trying get all the stored values begins with item_***
I know how to read and write with single key (example below)... but I am trying to get a list of items from shared_preferences where the key name begins with item_.
string
read: final myString = prefs.getString('my_string_key') ?? '';
write: prefs.setString('my_string_key', 'hello');
stringList
read: final myStringList = prefs.getStringList('my_string_list_key') ?? [];
write: prefs.setStringList('my_string_list_key', ['horse', 'cow', 'sheep']);
due to some reason, I don't want to store all the items in one list.... I want to store each item with separate key.
I searched in google and in stackoverflow, unfortunately no where found proper answer....
also I looked into this one, but not understood how to implement partial key search...
esetintis got to this first but I doodled this code so I guess I'll share it. But yes, you have to first get all of the keys in the shared preferences and then get the value for matching keys.
SharedPreferences prefs = await SharedPreferences.getInstance();
Set<String> keys = prefs.getKeys().where((key)=>key.startsWith('item_'));
for (String key in keys) {
String value = prefs.getString(key); // Throws an error if you store something other than a String
// Do your thing
}
I don't think there is a way to make such query. However, you can tackle the issue with some extra steps.
1 step :
Get all keys from SharedPreferences with prefs.getKeys() method. This will return a Set of keys. Now you can assign a List<String> keys = prefs.getKeys().where((k)=>k.startsWith('item_')) which will have the keys you want to get from the Storage.
2nd :
Iterate the filtered array and get the values you want by calling SharedPreferences, and save them to some variable.
Assuming that you have all the keys in a list, for example:
List<String> keys = ['item_001', 'item_103', 'item_007', 'item_059', 'other_key', 'blablabla'];
Now, you could iterate through all of them and checking the ones that starts with "item_", like this:
var itemKeys = [];
for(var i=0;i<keys.length;i++){
if (keys[i].startsWith('item_')) {
itemKeys.add(keys[i]);
}
}
print(itemKeys); // [item_001, item_103, item_007, item_059]
In the above example, itemKeys contains all the needed keys for you. What you could also do is to add the proper logic to fetch values from the shared preferences inside the if statement in the loop:
var result = [];
for(var i=0;i<keys.length;i++){
if (keys[i].startsWith('item_')) {
result.add(prefs.getString(keys[i]) ?? '');
}
}
result should contain what are you looking for.
I am making a search request on the List with the Provider pattern.
List<Device> _devices = [
Device(one: 'Apple', two: 'iphone'),
Device(one: 'Samsung', two: 'Galaxy')
];
And Query is like this
List<Device> queryQuery(String value) {
return _devices
.where((device) => device.one.toLowerCase().contains(value.toLowerCase()))
.toList();
the result I expect to get is iphone when I passed the value Apple.
But the result on the screen that I got is [instance of ‘Device’]
when I code like this
child: Text('${deviceData.getDevice('Apple')}'
I do know I should be using some kind of key using two... but I have no idea :-(
You serialized the wrong object.
What you did end-up being similar to:
Text(Device(one: 'Apple', two: 'iphone').toString());
But you don't want to do Device.toString(). What you want instead is to pass Device.two to your Text.
As such your end result is:
Text('${chordData.chordExpand('Apple').two}')
By the look of [Instance of 'Device'], it seems the function is returning a list so it is a good idea to check if the list is empty or not. if it is not empty, one of the elements is still needed to be selected. I guess it should be Text('${chordData.chordExpand('Apple')[0].two}') in case the list is not empty.
To summarize, use something like this to handle the case when list is empty
// Inside your build method before returning the widget
var l = chordData.chordExpand('Apple'); // Returns a list of devices
String textToWrite; // Here we will store the text that needs to be written
if(l.isEmpty) textToWrite = 'No results'; // If the filter resulted in an empty list
else textToWrite = l[0].two; // l[0] is an instance of a device which has a property called two. You can select any instance from the list provided it exists
return <Your Widget>(
.....
Text(textToWrite),
.....
);
I am writing a test which should iterate until a partial matching text is found . Once found , it should do some thing. Here is my code.
let getName = await $$('.button').getText();
if (getName === 'New name') {
// do something here
}
My test doesn't iterate even though there exists a matching name. It should also consider partials tests, for instance New name 1.
Appreciate your suggestions.
My answer is a shot in a dark due to lack of details in your question, but I'll try to guess your problem.
$$().getText() returns array of strings, thus your code must be
let names = await $$('.button').getText();
for (let i=0; i<names.length; i++) {
if (names[i].includes('New name')) {
// do something here
}
}
But when you await $$().getText(), and there are more than ~10 elements, be ready to face this error Random occurrences of Failed: ECONNREFUSED connect ECONNREFUSED 127.0.0.1 when running protractor tests
Actually, I must include another guess here based on an assumption you'll need to interact with the first element that matches condition
let $newNameElement = await $$('.button').filter( $elem =>
(await $elem.getText()).toLowerCase().includes('new name');
).get(0);
// do whatever you want with your $newNameElement
I'm trying to test out Firebase to allow users to post comments using push. I want to display the data I retrieve with the following;
fbl.child('sell').limit(20).on("value", function(fbdata) {
// handle data display here
}
The problem is the data is returned in order of oldest to newest - I want it in reversed order. Can Firebase do this?
Since this answer was written, Firebase has added a feature that allows ordering by any child or by value. So there are now four ways to order data: by key, by value, by priority, or by the value of any named child. See this blog post that introduces the new ordering capabilities.
The basic approaches remain the same though:
1. Add a child property with the inverted timestamp and then order on that.
2. Read the children in ascending order and then invert them on the client.
Firebase supports retrieving child nodes of a collection in two ways:
by name
by priority
What you're getting now is by name, which happens to be chronological. That's no coincidence btw: when you push an item into a collection, the name is generated to ensure the children are ordered in this way. To quote the Firebase documentation for push:
The unique name generated by push() is prefixed with a client-generated timestamp so that the resulting list will be chronologically-sorted.
The Firebase guide on ordered data has this to say on the topic:
How Data is Ordered
By default, children at a Firebase node are sorted lexicographically by name. Using push() can generate child names that naturally sort chronologically, but many applications require their data to be sorted in other ways. Firebase lets developers specify the ordering of items in a list by specifying a custom priority for each item.
The simplest way to get the behavior you want is to also specify an always-decreasing priority when you add the item:
var ref = new Firebase('https://your.firebaseio.com/sell');
var item = ref.push();
item.setWithPriority(yourObject, 0 - Date.now());
Update
You'll also have to retrieve the children differently:
fbl.child('sell').startAt().limitToLast(20).on('child_added', function(fbdata) {
console.log(fbdata.exportVal());
})
In my test using on('child_added' ensures that the last few children added are returned in reverse chronological order. Using on('value' on the other hand, returns them in the order of their name.
Be sure to read the section "Reading ordered data", which explains the usage of the child_* events to retrieve (ordered) children.
A bin to demonstrate this: http://jsbin.com/nonawe/3/watch?js,console
Since firebase 2.0.x you can use limitLast() to achieve that:
fbl.child('sell').orderByValue().limitLast(20).on("value", function(fbdataSnapshot) {
// fbdataSnapshot is returned in the ascending order
// you will still need to order these 20 items in
// in a descending order
}
Here's a link to the announcement: More querying capabilities in Firebase
To augment Frank's answer, it's also possible to grab the most recent records--even if you haven't bothered to order them using priorities--by simply using endAt().limit(x) like this demo:
var fb = new Firebase(URL);
// listen for all changes and update
fb.endAt().limit(100).on('value', update);
// print the output of our array
function update(snap) {
var list = [];
snap.forEach(function(ss) {
var data = ss.val();
data['.priority'] = ss.getPriority();
data['.name'] = ss.name();
list.unshift(data);
});
// print/process the results...
}
Note that this is quite performant even up to perhaps a thousand records (assuming the payloads are small). For more robust usages, Frank's answer is authoritative and much more scalable.
This brute force can also be optimized to work with bigger data or more records by doing things like monitoring child_added/child_removed/child_moved events in lieu of value, and using a debounce to apply DOM updates in bulk instead of individually.
DOM updates, naturally, are a stinker regardless of the approach, once you get into the hundreds of elements, so the debounce approach (or a React.js solution, which is essentially an uber debounce) is a great tool to have.
There is really no way but seems we have the recyclerview we can have this
query=mCommentsReference.orderByChild("date_added");
query.keepSynced(true);
// Initialize Views
mRecyclerView = (RecyclerView) view.findViewById(R.id.recyclerView);
mManager = new LinearLayoutManager(getContext());
// mManager.setReverseLayout(false);
mManager.setReverseLayout(true);
mManager.setStackFromEnd(true);
mRecyclerView.setHasFixedSize(true);
mRecyclerView.setLayoutManager(mManager);
I have a date variable (long) and wanted to keep the newest items on top of the list. So what I did was:
Add a new long field 'dateInverse'
Add a new method called 'getDateInverse', which just returns: Long.MAX_VALUE - date;
Create my query with: .orderByChild("dateInverse")
Presto! :p
You are searching limitTolast(Int x) .This will give you the last "x" higher elements of your database (they are in ascending order) but they are the "x" higher elements
if you got in your database {10,300,150,240,2,24,220}
this method:
myFirebaseRef.orderByChild("highScore").limitToLast(4)
will retrive you : {150,220,240,300}
In Android there is a way to actually reverse the data in an Arraylist of objects through the Adapter. In my case I could not use the LayoutManager to reverse the results in descending order since I was using a horizontal Recyclerview to display the data. Setting the following parameters to the recyclerview messed up my UI experience:
llManager.setReverseLayout(true);
llManager.setStackFromEnd(true);
The only working way I found around this was through the BindViewHolder method of the RecyclerView adapter:
#Override
public void onBindViewHolder(final RecyclerView.ViewHolder holder, int position) {
final SuperPost superPost = superList.get(getItemCount() - position - 1);
}
Hope this answer will help all the devs out there who are struggling with this issue in Firebase.
Firebase: How to display a thread of items in reverse order with a limit for each request and an indicator for a "load more" button.
This will get the last 10 items of the list
FBRef.child("childName")
.limitToLast(loadMoreLimit) // loadMoreLimit = 10 for example
This will get the last 10 items. Grab the id of the last record in the list and save for the load more functionality. Next, convert the collection of objects into and an array and do a list.reverse().
LOAD MORE Functionality: The next call will do two things, it will get the next sequence of list items based on the reference id from the first request and give you an indicator if you need to display the "load more" button.
this.FBRef
.child("childName")
.endAt(null, lastThreadId) // Get this from the previous step
.limitToLast(loadMoreLimit+2)
You will need to strip the first and last item of this object collection. The first item is the reference to get this list. The last item is an indicator for the show more button.
I have a bunch of other logic that will keep everything clean. You will need to add this code only for the load more functionality.
list = snapObjectAsArray; // The list is an array from snapObject
lastItemId = key; // get the first key of the list
if (list.length < loadMoreLimit+1) {
lastItemId = false;
}
if (list.length > loadMoreLimit+1) {
list.pop();
}
if (list.length > loadMoreLimit) {
list.shift();
}
// Return the list.reverse() and lastItemId
// If lastItemId is an ID, it will be used for the next reference and a flag to show the "load more" button.
}
I'm using ReactFire for easy Firebase integration.
Basically, it helps me storing the datas into the component state, as an array. Then, all I have to use is the reverse() function (read more)
Here is how I achieve this :
import React, { Component, PropTypes } from 'react';
import ReactMixin from 'react-mixin';
import ReactFireMixin from 'reactfire';
import Firebase from '../../../utils/firebaseUtils'; // Firebase.initializeApp(config);
#ReactMixin.decorate(ReactFireMixin)
export default class Add extends Component {
constructor(args) {
super(args);
this.state = {
articles: []
};
}
componentWillMount() {
let ref = Firebase.database().ref('articles').orderByChild('insertDate').limitToLast(10);
this.bindAsArray(ref, 'articles'); // bind retrieved data to this.state.articles
}
render() {
return (
<div>
{
this.state.articles.reverse().map(function(article) {
return <div>{article.title}</div>
})
}
</div>
);
}
}
There is a better way. You should order by negative server timestamp. How to get negative server timestamp even offline? There is an hidden field which helps. Related snippet from documentation:
var offsetRef = new Firebase("https://<YOUR-FIREBASE-APP>.firebaseio.com/.info/serverTimeOffset");
offsetRef.on("value", function(snap) {
var offset = snap.val();
var estimatedServerTimeMs = new Date().getTime() + offset;
});
To add to Dave Vávra's answer, I use a negative timestamp as my sort_key like so
Setting
const timestamp = new Date().getTime();
const data = {
name: 'John Doe',
city: 'New York',
sort_key: timestamp * -1 // Gets the negative value of the timestamp
}
Getting
const ref = firebase.database().ref('business-images').child(id);
const query = ref.orderByChild('sort_key');
return $firebaseArray(query); // AngularFire function
This fetches all objects from newest to oldest. You can also $indexOn the sortKey to make it run even faster
I had this problem too, I found a very simple solution to this that doesn't involved manipulating the data in anyway. If you are rending the result to the DOM, in a list of some sort. You can use flexbox and setup a class to reverse the elements in their container.
.reverse {
display: flex;
flex-direction: column-reverse;
}
myarray.reverse(); or this.myitems = items.map(item => item).reverse();
I did this by prepend.
query.orderByChild('sell').limitToLast(4).on("value", function(snapshot){
snapshot.forEach(function (childSnapshot) {
// PREPEND
});
});
Someone has pointed out that there are 2 ways to do this:
Manipulate the data client-side
Make a query that will order the data
The easiest way that I have found to do this is to use option 1, but through a LinkedList. I just append each of the objects to the front of the stack. It is flexible enough to still allow the list to be used in a ListView or RecyclerView. This way even though they come in order oldest to newest, you can still view, or retrieve, newest to oldest.
You can add a column named orderColumn where you save time as
Long refrenceTime = "large future time";
Long currentTime = "currentTime";
Long order = refrenceTime - currentTime;
now save Long order in column named orderColumn and when you retrieve data
as orderBy(orderColumn) you will get what you need.
just use reverse() on the array , suppose if you are storing the values to an array items[] then do a this.items.reverse()
ref.subscribe(snapshots => {
this.loading.dismiss();
this.items = [];
snapshots.forEach(snapshot => {
this.items.push(snapshot);
});
**this.items.reverse();**
},
For me it was limitToLast that worked. I also found out that limitLast is NOT a function:)
const query = messagesRef.orderBy('createdAt', 'asc').limitToLast(25);
The above is what worked for me.
PRINT in reverse order
Let's think outside the box... If your information will be printed directly into user's screen (without any content that needs to be modified in a consecutive order, like a sum or something), simply print from bottom to top.
So, instead of inserting each new block of content to the end of the print space (A += B), add that block to the beginning (A = B+A).
If you'll include the elements as a consecutive ordered list, the DOM can put the numbers for you if you insert each element as a List Item (<li>) inside an Ordered Lists (<ol>).
This way you save space from your database, avoiding unnecesary reversed data.
Consider the below program
private static bool CheckFactorPresent(List<FactorReturn> factorReturnCol)
{
bool IsPresent = true;
StringBuilder sb = new StringBuilder();
//Get the exposure names from Exposure list.
//Since this will remain same , so it has been done outside the loop
List<string> lstExposureName = (from item in Exposures
select item.ExposureName).ToList<string>();
foreach (FactorReturn fr in factorReturnCol)
{
//Build the factor names from the ReturnCollection dictionary
List<string> lstFactorNames = fr.ReturnCollection.Keys.ToList<string>();
//Check if all the Factor Names are present in ExposureName list
List<string> result = lstFactorNames.Except(lstExposureName).ToList();
if (result.Count() > 0)
{
result.ForEach(i =>
{
IsPresent = false;
sb.AppendLine("Factor" + i + "is not present for week no: " + fr.WeekNo.ToString());
});
}
}
return IsPresent;
}
Basically I am checking if all the FactorNames[lstFactorNames] are present in
ExposureNames[lstExposureName] list by using lstFactorNames.Except(lstExposureName).
And then by using the Count() function(if count() > 0), I am writing the error
messages to the String Builder(sb)
I am sure that someone can definitely write a better implementation than the one presented.
And I am looking forward for the same to learn something new from that program.
I am using c#3.0 and dotnet framework 3.5
Thanks
Save for some naming convention issues, I'd say that looks fine (for what I can figure out without seeing the rest of the code, or the purpose in the effort. The naming conventions though, need some work. A sporadic mix of ntnHungarian, PascalCase, camelCase, and abbrv is a little disorienting. Try just naming your local variables camelCase exclusively and things will look a lot better. Best of luck to you - things are looking good so far!
- EDIT -
Also, you can clean up the iteration at the end by just running a simple foreach:
...
foreach (var except in result)
{
isPresent = false;
builder.AppendFormat("Factor{0} is not present for week no: {1}\r\n", except, fr.WeekNo);
}
...