I am attempting to write my first program using Qt5. I found a tutorial (zetcode.com/gui/qt5) with a number of examples, which all used dynamic layout creation. I'm trying to create a nested layout configuration, but I'm having a problem with specifying the parent parameter of the layout constructor. When I use the main window as the parent for the main layout and its sub-layouts, I get an error message, apparently telling me that QWidget can have only one QLayout. The window looks OK, but I haven't implemented all my functionality yet (slots and other code), so I don't know what, if anything, is broken. If I omit the parent parameter from the sub-layouts, I get no error messages and the window looks OK as well, but again I'm wondering whether this would affect my subsequent code additions.
Can anyone explain to me the significance of a layout's parent? I've noted that specification of the parent window in the layout's constructor is apparently not sufficient, because all of the examples I've seen call setLayout() at the end of the window's constructor. In particular, will my omission of a parent ever cause problems?
The "rules" are that there can be at most one top level layout on a given widget, and that widgets can be only children of other widgets, not of layouts. So what happens is that:
when you set a layout on a widget, the widget will take ownership of that layout;
when you add widgets on a layout, these widgets will be reparented to the widget the layout is/gets installed upon;
when you add a layout inside another layout, the inner layout becomes a child of the outer layout.
What you're probably seeing is a side-effect of creating a layout with a widget as parent, as in
QLayout *layout = new SomeLayout(widget);
This will try to install the layout on widget, and fail in case there's already one. The good news is, you can pretty much ignore passing parents around and rely on the system to do "the right thing". For instance:
MyWidget::MyWidget(QWidget *parent)
: QWidget(parent)
{
QHBoxLayout *mainLayout = new QHBoxLayout; // top level layout
QVBoxLayout *subLayout1 = new QVBoxLayout; // sub layout 1 stuff
QPushButton *button = new QPushButton("button");
subLayout1->addWidget(button);
// create more widgets...
mainLayout->addLayout(subLayout1);
QVBoxLayout *subLayout2 = new QVBoxLayout; // sub layout 2 stuff
QLineEdit *edit = new QLineEdit;
subLayout2->addWidget(edit);
mainLayout->addLayout(subLayout2);
setLayout(mainLayout);
}
This will correctly create a layout hierarchy and a parent/child relation so that nothing will get leaked.
Related
I've read the documentation of this attribute:
An additional flag to be used with 'snap'. If set, the view will be snapped to its top and bottom margins, as opposed to the edges of the view itself.
https://developer.android.com/reference/com/google/android/material/appbar/AppBarLayout.LayoutParams.html#scroll_flag_snap
But I can't observe any actual effect in my app. What margin are they talking about? Every margin on the CollapsingToolbarLayout (on which this attribute is set) completely destroys the layout.
Not sure if it's useful yet, but here is the difference:)
If you pass snap as scroll flag, then it will move your view (in my case this search bar, it's linearLayout) to it's edge NOT INCLUDING the margin_layout
Then I've tried snap|snapMargin and it moved with the margin
P.S. No idea why snapMargin doesn't work without snap ¯\_(ツ)_/¯
This attribute is responsible for a scrolling behavior of AppBarLayout and its children. You can apply it directly to AppBarLayout or on the inside views, in the xml layout of your AppCompatActivity. It has to be an instance of AppCompatActivity if you want to use AppBar features. Also, the design library must be included in Gradle dependencies, like so: implementation 'com.android.support:design:26.1.0'
Please refer this link:-[https://medium.com/#tonia.tkachuk/appbarlayout-scroll-behavior-with-layout-scrollflags-2eec41b4366b][1]
In PyQt, I have a dialog that spawns another dialog (when you click a button to do so in the first dialog). I want to maintain a strong parent-child relationship, for garbage collection purposes, and to make the .findChild and .findChildren functions usable.
The root of the question may be: how do you use .setParent() but still have the object in question be shown as a separate window, rather than shown within the parent widget?
The 'parent' dialog (actually a container widget within a tab within a dialog) is 'newEntryWidget'. It spawns 'clueDialog' when a signal (not shown here) calls newEntryWidget.quickTextClueAction as a slot. Visually, clueDialog should be a "top level window" with its own banner, its own window attributes (I want to keep it on top of everything else), etc.
class newEntryWidget(QWidget,Ui_newEntryWidget):
def __init__(self,parent,sec=0,formattedLocString='',fleet='',dev='',origLocString='',amendFlag=False,amendRow=None):
QDialog.__init__(self)
self.parent=parent # just an attribute; not the same as setParent
...
...
def quickTextClueAction(self):
self.newClueDialog=clueDialog(self,self.ui.timeField.text(),self.ui.teamField.text(),self.ui.radioLocField.text(),lastClueNumber+1)
self.newClueDialog.show()
class clueDialog(QDialog,Ui_clueDialog):
def __init__(self,parent,t,callsign,radioLoc,newClueNumber):
QDialog.__init__(self)
self.parent=parent # just an attribute; not the same as setParent
...
...
Right now, since I am using self.parent=parent, which is just an attribute and not true "parent/child relationship" in Qt terms, clueDialog does display as a top level window, which is what I want:
But, if I add 'self.setParent(parent)' in the clueDialog init function, I get this:
How can I preserve the top-level-window behavior, and have the real-honest-parent-child-relationship so that .findChild(clueDialog) will work from within the newEntryWidget object?
Ultimately, I want to enforce that the newEntryWidget object should not be closed if it still has and 'child' clueDialogs open.
Instead of calling .setParent, call QDialog.__init__(self, parent) which constructs the clue dialog with a parent from the beginning. Setting it this way allows Qt establishes the parent-child relationship at the beginning of clueDialog's lifetime.
I believe this will fix both your issues: 1) the clue window frame, caption, etc. will be painted, 2) you will be able to iterate for proper children of newEntry.
I want to add a new View to a Layout dynamically by layout.addView(view) method. The new View is not supposed to be visible, but I want it's Display List to be created so it doesn't have to redraw (call onDraw method) itself when I decide to show it (by animation, for example fade in).
I run this code:
customView = new CustomView(this.getContext());
customView .setAlpha(0.0f);
this.addView(customView ); // 'this' is RelativeLayout instance in this case
onDraw method gets called for customView and everything is fine. However, when I change anything in my layout (push a button, scroll, anything that invalidates layout), the onDraw method for my customView is called second time. After that, it isn't called any more if I don't invalidate my customView (correct behaviour).
I don't know why Android behaves this way. I want it to create customView, call onDraw, create a Display List for it, and not call onDraw any more until I invalidate my view. To sum up, onDraw is supposed to be called once.
And it has nothing to do with initial invisibility of customView, if alpha is set to 0.5f, behaviour is the same.
My question is, how to make Android call onDraw only once?
And if Android really has to call onDraw twice, then what should I do to enforce it to do it in some code right after this.addView(view); without setting up any timers because THAT would be totally ugly.
The behavior you are describing is ok and is a part of the android framework for view object -
Drawing
Drawing is handled by walking the tree and rendering each view that
intersects the invalid region. Because the tree is traversed in-order,
this means that parents will draw before (i.e., behind) their
children, with siblings drawn in the order they appear in the tree. If
you set a background drawable for a View, then the View will draw it
for you before calling back to its onDraw() method. Note that the
framework will not draw views that are not in the invalid region. To
force a view to draw, call invalidate()
(Taken from the official google android API docs).
Meaning your custom view is contained by the same view that contains the button\scrollbar etc. If you don't want it to be rendered everytime the onDraw method is called for the subtree your view resides in you can set the view's boolean flag to false - use setWillNotDraw() to do that. (you should place it on the activity's onCreate in order to render the view set this flag to false (which is also the default) and use invalidate() whenever you want to render the view).You can read the official google docs for further information.
i am new to GWT and GWTP and the question sounds stupid.. Can I make an abstract PresenterWidget or similiar?
Like in normal Java extending the "class" and reuse / extend the logic. But not only the class, the whole thing of View and Presenter. I try to explain my initial situation and maybe you have another idea.
The image hopefully helps to explain it. The "Main-Tab" and every other tab consists of a collection of views which have the same base structure and the same logic.
the base structure consists of
border around EVERYTHING
an image (the wwitch)
a title
a textarea
a PresenterWidget which is added to a contentSlot of the parent (the menu left)
and below the base are view specific components like buttons, text or any other widget. So a main part of the view with logic is repeading. If the switch is "toggled" the view is hidden (the textarea and any childs / view specific components) like the lowest view in the picture. Furthermore the PresenterWidget left changes the color.
The logic is working, but now I am searching a proper way to solve this without repeading code and the possibility to add child elements which are hidden as well by toggling the switch. Can I add to a PresenterWidget child widgets and define where there should be added? like: Even if this is possible, it feels a bit inconvenient.
Thanks in advance.
I just want to post the solution:
I have now a simple Composite (KPICommonView) for the switch, title and the description. It got another FlowPanel below the description, where the specific components will be added later. For this the Composite implements "HasWidgets" and overrides the "add(Widget w)"-method which is called by UiBinder if the Widget is added and has child elements.
<own:KPICommonView title="First Header" description="I am a happy description :)" anchorToken="{nameAnchors.getFirst}">
<g:Label>child component</g:Label>
</own:KPICommonView>
I am not sure if I do a PresenterWidget for every segment and every PresenterWidget has one of the KPICommonView added, or if I do one normal Presenter which adds more than one of the CommonViews.
The CommonView furhter creates the PresenterWidget for the menu item on the side. It gets the attributes from the constructor (anchorToken, title) and adds it to the slot (which happens ugly, because the View has hard coded the parent saved to call "addInSlot()". The repeading code for the switch is handled by the KPICommonView.
Background/Context:
I have a HBox as a parent and many child Nodes (Buttons, TextFields, Labels…). The HBox is a child of other container (BorderPane/VBox/Grid)
My questions:
How do I dynamically remove/exclude the parent (HBox) and all its children from layout?
I am looking for some three-state property on Node (like in Microsoft WPF):
Visible – visible and participate in layout
Collapsed – is not visible and do not participate in layout (applies to its children as well)
Hidden – is not visible but participate in layout
http://msdn.microsoft.com/en-us/library/ms590101.aspx
What options does JavaFX offer?
My solutions so far:
hBox.setManaged(false);
this work only for HBox, its children are still present
root.getChildren().remove(hBoxTop);
root.getChildren().add(hBoxTop);
Well, this looks like it could work.., but for example in case of root being BorderPane, once I remove/add and remove the HBox, the space after it remains unused. I already tried requestLayout() but id does not force thr rrot to fill it. Am I missing something? Is it correct approach to this problem?
Edited:
Well, I got this working.
Dynamically removing and adding for this specific case can be achieved by:
Remove:
root.setTop(null);
Add:
root.setTop(hBoxTop);
When I did not call setTop(null) on removal, BorderPane still reserved space for HBox (even after removal from its children).
IMHO: it is not very good model as it is parent-container specific. For example if I change, BorderPane to VBox a I had to change these methods as well. For VBox, remove/add on children collection works but I need to remember index so that HBox appears at same place after calling add.
Using root.setTop(null) is not a good idea because as you say it's specific to BorderPane.
I think the best solution is to use:
root.getChildren().remove(yourPane);
And use layout methods to place your other childrens as you want.
But maybe you should not use a BorderPane in the first place with the behaviors you want in your application.
Notice you can also do root.getChildren().clear() to remove all component and add it again to your layout but differently.