I'm trying to get the update function in Flame game to work. I have a global variable called newInstructions that's a list that gets updated by a separate function. I want the update function to check when there's a new addition to the list and call a function (populateInfo) with that list as input. After looking at some of the documentation, I've come up with what I think would be the correct code, but it keeps returning this error:
The method 'query' isn't defined by the type 'List'
I think that part of this might come from my not fully understanding what the update/query methods do. With that, what does the query method do and what type should it be? How would I go about changing my code to fix that error?
Here is the update function that I wrote:
#override
void update(double dt){
final instructions = newInstructions.query<List>();
populateInfo(instructions);
}
With that, what does the query method do and what type should it be?
query is a Flame specific method that is used on the OrderedSet in each component where the children are stored, it is used to get children of a specific type. For example to get all Player components:
children.query<Player>();
How would I go about changing my code to fix that error?
Since you want to react to when something is added the newInstructions list you shouldn't do this check in update since this method runs at least 60 times per seconds, it's better to just react once when there is a new instruction added.
This can be done in a few different ways, you could for example put the newInstructions list in a class that you then have an add method on that both adds the instruction to a list contained within the class, and also calls populateInfo. You could also wrap the list in a ChangeNotifier like this.
Related
I have created a method to toggle transaction type, like converting expense to income and income to expense...
and I created following method
void swapTransaction(TransactionModel transaction)
{
transaction.isExpense=!transaction.isExpense;
update();
}
it worked fine but than I was forced to apply following method,
void swapTransaction(TransactionModel transaction)
{
int index=_transactions.indexOf(transaction);
_transactions[index].isExpense=!_transactions[index].isExpense;
update();
}
here I want to know what is the better method to apply... is there any big difference?
I'm not sure if such questions are suitable for this site, as it can be "opinion based" but here's my take:
I think the second method is better since you are updating the actual _transactions list, but in the first example, you are just updating what's getting passed into the function - the TransactionModel, so you're not actually changing the list of _transactions.
According to me, second one is better.
In first one you are passing one copy of object to update, which is just used within that function. While in second one you are actually updating your actual list of transaction, which you used to display.
I have written and extension on Stream that allows me to call .watch(<some state>) and automatically keep the widget updated. It works really well, however, I call setState on passed states from the extension and because of this I get a warning saying The member 'setState' can only be used within instance members of subclasses of 'package:flutter/src/widgets/framework.dart'. My question is why is this not recommended/allowed?. To clarify, I get why I am getting the warning - I'm calling setState from another class - but why does Flutter "care" if I do this?
I have tried to find information on any reason for this, but I can only find the obvious workaround of adding a helper function, and no reason is given.
There could be two possible reasons why you are getting this error:
You are using a static or final keyword somewhere where you declare a state
You are unable to setState, because the extension is updating the state of the widget already
Let me know if you need any further help or I understood you wrong!
Getting wired issue like main array has been changed if changed value of another array. I think issue is about copying same address, not sure but just thinking of it. I have tried from last 3 hours but unable to get rid from it.
Look at below illustration to get better idea.
List<page> _pageList;
List<page> _orderList = [];
_pageList = _apiResponse.result as List<page>;
_orderList.add(_pageList[0].element);
_orderList[0].title = "XYZ"
//--> Here if I change the `_orderList[0].title` then it also change the `title` inside "_pageList"
How can we prevent the changes in main array?
I got same issue in my one of the project. What I have done is, use json to encode and decode object that help you to make copy of the object so that will not be affected to the main List.
After 3rd line of your code, make changes like below
Elements copyObject = Elements.fromJson(_pageList[0].element.toJson());
// First of all you have to convert your object to the Map and and map to original object like above
_orderList.add(copyObject);
Hope that will help you.
You can use a getter function to create a copy of your list and use that instead of
altering your actual list.
example:
List<Page> get orderList{
return [..._orderList];
}
Lists in Dart store references for complex types, so this is intended behaviour.
From your code:
_orderList.add(_pageList[0].element);
_orderList[0] and _pageList[0].element point to the same reference (if they are non-primitive).
There is no general copy() or clone() method in dart, as far as i know. So you need to copy the object yourself, if you want a separate instance. (see this question)
This library I found that handles music playing has the following variable public.
void Function() onCompleted;
I want to change the icon of a button when the track is finished, so that it returns to a play icon.
I tried using musicPlayer.OnCompleted(() { **stuff** }); but that gives me a syntax error Too many positional arguments: 0 expected, but 1 found.
How do I subscribe on that event, or how do I check if OnCompleted has been called?
I am still pretty new to dart but can't wrap my head around this one. I tried subscribing like in Angular or looking up if there's a different syntax for it, but I am at a loss.
Presumably you have to set onCompleted to something, specifically a function taking no parameters and returning void.
It would be normal to provide something like this in the constructor. Is there a named, optional parameter for this? Alternatively, there may be a setter.
Let's assume there's a setter. You could write:
musicPlayer.onCompleted = (){/* do stuff*/};
Hi I have a situation where I need to look up the number of recently viewed products on catalog/product/view.phtml. In the recently viewed 'product_viewed.phtml' file it calls
$_products = $this->getRecentlyViewedProducts()
to get the recently viewed. How would I access this method from within the catalog/product/view.phtml file?
I don't know where this method is. I've tried searching for it but it doesn't seem to exist. When I write click it in Netbeans and click go to declaration it takes me to
class Mage_Reports_Block_Product_Viewed extends Mage_Reports_Block_Product_Abstract
Actually on the class itself. This class only has _toHtml(), getCount(), and getPageSize() methods.
I just need to know whether there are any recently viewed products.
Any help most appreciated!
Billy
If you look into 'Mage_Reports_Block_Product_Viewed', you will notice:
$this->setRecentlyViewedProducts($this->getItemsCollection());
That 'getItemsCollection' method is defined in the abstract class... And you will notice this abstract class will create a model based on $_indexName defined in the (subclassed) block.
If you just want the collection, you can probably get away with:
$_products = Mage::getModel('reports/product_index_viewed')->getCollection();
And then adding whatever you want to the collection:
$_products
->addAttributeToSelect('*')
->setAddedAtOrder();
// optionally add other methods similar to Mage_Reports_Block_Product_Abstract::getItemsCollection
Another approach that might be more suited would be to create the original block:
$productViewedBlock = $this->getLayout()->createBlock('reports/product_viewed');
On which you can simply call whatever you want:
$_collection = $productViewedBlock->getItemsCollection();
$_count = $productViewedBlock->getCount();
The getRecentlyViewedProducts function is a magical getter that gets the data that was set with setRecentlyViewedProducts in app/code/core/Mage/Reports/Block/Product/Viewed.php (which builds it using app/code/core/Mage/Reports/Block/Product/Abstract.php's function _getRecentProductsCollection).
This is complicated stuff that you don't want to reproduce; its better, IMO to make your own Block that extends Mage_Catalog_Block_Product_Abstract that will give you access to the same functionality, and drop your new block into the page you're working on.