I'm creating a GUI inventory widget for the player, basically I have created the widget, it shows, I want to toggle the widget on and off, what I have now is, I can press the inventory key and it shows, on the A flip flop, but when for the B flip flop, it doesn't hide the inventory as it should be, although it prints the string, its not removing the widget as it should be, what should I add to my player blue print?
In your code on both sides of the flip-flop you are creating the widget, make sure the widget you are trying to hide is the one you created.
For that, remove the "Create Inventory Widget" node from the B part of the flip-flop and connect the "Set Visibility" node 'target' to the "Create Inventory Widget" 'return value' located in the A part of your flip-flop.
It's also recommended to save it as a variable to avoid confusion in your code if you ever need to something with the widget visibility again.
Related
I have a GestureDetector inside a ListView and a CustomFilter widget in my Scaffold.
When I filter or change me showList in CustomFiter Widget it seems to be updated because I print the correct value from my CustomValueNotifier.
When it comes to my parent widget which is supposed to show my showList inside the GestureDetector the value is not updated at all and is at all times an empty list.
So the problem seems to be between the connection of my parent widget which hold both the filter widget, which upadtes the list, and my CustomValueNotifier, which takes the updated value but as I said before does not provide it at the widget.
Right now I also do the onnection with getter and setter so in the code im goin to show the showList will be taken the correct value from the getShowList() method. The problem is it doesnt change when the filter is being activated, on change of each filter, but after that when i press somewhere inside the gesturedetector again.
I have tried Change Notifier,Value Notifier, Provider does not seem to be what i can use in this example, setState but of course it updates on click in gestureDetector later
I'm building a chat app and I want to achieve a ListView() that loads up like its reverse property is set to true i.e showing the end of the ListView on build. The reason I don't want to set the reverse property to true is because, if the items in the ListView do not fill up the screen, they are aligned to the bottom (cannot use shrinkWrap because of performance), and also because it reverses the order of the items and to show new elements at the bottom of the list, I'd need to use a spread operator and I'm worried about performance since the Map from which I render from can grow significantly.
I have also tried using the ScrollController's jumpTo method inside a SchedulerBinding.instance!.addPostFrameCallback but the user can see the scrolling and
it also causes it to jump like it's attempting to scroll beyond what is contained in the ListView. I have also used ScrollablePositionedList and set the index to which I want to scroll, but this jumps also.
Is there any way I can achieve my aim without any drawbacks visually or performance-wise?
You have the correct idea: in the initState, jump to the end. The end of the list can be obtained from position.maxScrollExtent. When done correctly, this does not create any visual or performance drawbacks. For example:
void initState() {
super.initState();
WidgetsBinding.instance.addPostFrameCallback((timeStamp) {
_controller.jumpTo(_controller.position.maxScrollExtent);
});
}
The _controller should be the ScrollController passed to the list.
I'm new to Flutter and I'm trying to build a chat application and I've watched several tutorials. To view the chat messages list/history, almost every tutorial is doing something like this: (I'm shortening the code to get to the point)
List<Widget> messages = api.listOfMessages();
return Column(children: messages);
Now every time there's a new message, messages is updated and the column is re-built. I gotta say the word "rebuild" sounds an expensive procedure to me. Say 2 users have been chatting 500 lines. Now every time a new message is coming, 500 lines are getting rebuilt over an over.
I thought about putting an empty widget at the end of the list. So when a new message arrives, I just insert it to that empty widget and have that to rebuild only:
List<Widget> messages = api.listOfMessages();
return Column(children: [...messages, EmptyWidgetForNewMessage()];
But that looks like a hack and will cause a lot of nested widgets, because every new message must also insert another EmptyWidget etc...
How can I avoid rebuilding previous messages and only insert the new one to the view? (or rebuilding the entire list is not that big a deal?)
You can use sliver widget to build the messages that are visible in viewport(or within cacheExtent).
Like ListView.build, ListView.separated, from the doc of ListView.build:
if the list view's children are
created in advance, or all at once when the [ListView] itself is created,
it is more efficient to use the [ListView] constructor. Even more efficient, however, is to create the instances on demand using this constructor's itemBuilder callback.
Also, we will not fetch all messages from server at once. Instead we will fetch them in batches with query like ?page=1&size=20.
Note: There is a known issue with this widget, avoid using shrinkWrap: true if possible. See this issue
couple of improvements that you could target
Use ListView builder constructor instead of the column, only the children widget that are currently visible in the screen will be rendered whereas in Column widget all of its children will be rendered. Also ListView should be your preferred widget, because the Column widget is not scrollable, and there are chances of overflow exception, if the message list length is huge.
Use const constructor for all type of widgets returned by api.listOfMessages(), this will allow the compiler to reuse any rendered widget, meaning every time when a state change happens(in you case arrival of a new message) the entire tree is not re-rendered, the renderer will have the luxury of re using previously built message widget.
These two suggestions should take care of any performance bottlenecks, in short we would be rendering only the visible children widgets with ListView and we will be re reusing already rendered widget with the help of const constructor.
How can we show/hide widget inside another widget in flutter?
I have list of question which are inside list view builder I want to hide questions on user answer selection.
if you have all equations in question[] and whether to show them in show[], you could place into listbuild
return (bool[index] ? Card(child:Text(question[index])) : Container())
This returns the card in bool is true and the empty (not displayed container) otherwise.
(I think the other answer would do the trick too)
Another option you can consider though is using the Visibility widget to wrap the "question" widget and toggle the visible property based on a bool. To make this (or the above solution) work, you'd want to update the value of this bool using e.g. setState on the method called when,as you say, "user answer selection" happens.
Of course, if you have a more complicated application it might make more sense to use Provider for state management and wrap all of this in a Consumer.
I'm building a Qt plugin with multiple forms. I have a main form which has a tree widget placed on the left of the form.
I want to add items to this tree, such that clicking on these items would load the corresponding form on the same form. But I want the tree widget to be active so that I can select any other form also.
I was able to display a form on the main form using the following code:
Form1 *myform;
myform=new Form1(this);
myform->show();
where Form1 is the class of the form i intend to display. However this, covers up the tree widget also. And I have to do a string comparison of the item in tree being clicked to display the appropriate form.
Can someone please help me with this as I'm very new to Qt programming.
Thanks
ixM has a good suggestion. The first step should definitely be to use layouts in your main window - separating the tree from the rest of the window - where you are going to put your form. I would suggest using a splitter, because then the user can resize the two halves. You can set the splitter as the main widget of your CentralWidget in your main window.
QSplitter splitter = new QSplitter(CentralWidget);
splitter->setOrientation(Qt::Horizontal);
splitter->setHandleWidth(3);
splitter->setChildrenCollapsible(false);
MyTree= new QTreeWidget(splitter);
splitter->addWidget(MyTree);
Then add your tree widget to the splitter, which will be on the left side.
The next step is to add a placeholder widget on the right side of your splitter. We are also going to add a layout inside that widget. This layout is very important we are going to use it later.
QWidget WidgetRightSide = new QWidget(splitter);
QVBoxLayout setupLayout= new QVBoxLayout(WidgetRightSide);
setupLayout->setSpacing(0);
setupLayout->setContentsMargins(0, 0, 0, 0);
Now, at this point, this is where my answer really differs from the previous answer. You could use a QStackedWidget. That is certainly an option. The problem with that is that you have to create and load all your forms at the beginning. That uses way more memory, and will take longer to start up. That's not so bad if you have 2-5 forms, but when we are talking about 20, 30 or more forms that's really ugly.
So what I would suggest instead, is that when the user selects something in the tree, we will remove the old form, and add the newly selected form at that point.
When the selected item in the tree changes this is now what we have to do.
First, remove all the stuff from the previously selection form.
QLayoutItem *_Item;
while ((_Item = setupLayout->takeAt(0)))
delete _Item;
Next, figure out what form to show next, and create it.
QWidget *ActiveSetupForm = NULL;
if ( I need to load form 1)
{
ActiveSetupForm = new YourNewForm( WidgetRightSide);
}
else ...
And lastly, add your new form to our layout.
if(ActiveSetupForm)
{
setupLayout->addWidget(pActiveSetupForm);
}
Just as a side note. Layouts are tricky to do by hand. I would strongly suggest that you look into using the QtDesigner when you are creating your forms. It makes life soooo much easier. If you would like to know more about it check out this link.
I don't exactly understand what you are trying to achieve but the bit of code you are showing suggests that you do not use the layouts provided by Qt.
If your goal is to be able to dynamically load a form depending on the item that was clicked in the tree, you could achieve that by having a layout (let's say QHBoxLayout) where you would insert your tree and a QStackedWidget in which you could "store" each form (by using addWidget()) and choose which one you want to display by calling setCurrentIndex().