I have a custom control child component. When i try to set a value updated in parent component, the child is not getting the updated value. Please let me know what i am doing wrong here.
parent .html
<child-component
[config]="{ getPage: getSelectInfinitePage(), multiple: true }"
[(ngModel)]="selectedEntityItems" //in the child compoennt, this always coming as empty
[disabled]="!hasSubjectType"
[placeholder]="placeholderText"
name="selectInfinite"
(onChange)="onCustomItemChange()"
>
</child-component>
parent .ts
this.selectedEntityItems = ['a', 'b', 'c'];
Child component .ts (custom control using ControlValueAccessor)
writeValue(preselectedValues: ValueType): void {
this.values = preselectedValues; //here it is always coming empty
this.onModelChange(this.values);
}
Related
I am using ng-select as a custom form control and using controlvalueaccessor.
when i try to set value from parent component, the 'WriteValue' method in the child component is not getting the updated model value.
Parent component:
this.selectedEntityItems = ["a", "b", "c"];
<child-component
[config]="{ getPage: getSelectInfinitePage(), multiple: true }"
[(ngModel)]="selectedEntityItems" //the new values set to this variable is not getting updated in child component
[disabled]="!hasSubjectType"
[placeholder]="placeholderText"
name="selectInfinite"
(onChange)="onCustomItemChange()"
>
</child-component>
child-component:
publi writeValue(preselectedValues: string[]): void {
this.values = preselectedValues; //preselectedValues is always coming as undefined
this.onModelChange(this.values);
}
I have defined a MyElement element (in the MyElement.qml file) as the following:
Rectangle {
Item {
}
Component.onCompleted: {
console.warn(children.length)
}
}
Let's call the Item element defined within MyElement the internal child. Now, I'm using the MyElement element in the following way:
MyElement {
Item {
}
}
Here another one Item element is used as a child of MyElement. Let's call this Item element the external child. To understand my question below one should clearly understand the difference between internal and external children.
The output for the presented code will be 2, i.e. both Item elements are calculated as children.
In the future I want to iterate in the block Component.onCompleted only over external children, not over internal (external children go after internal). But for this I have to know a children index from which I have to start (in the given example this index is 1). Is there a way to get this index or, in other words, the number of internal children? Thanks.
There is no internal mechanism in Qt to distinguish internal children from those which are defined outside of the own QML definition.
My workaround is as follow
//MyElement.qml
Rectangle {
id: root
readonly property Item last_item: lastone
Item {
id: someitem
}
Item {
id: lastone
}
Component.onCompleted: {
var external_started = false;
for(var i = 0 ; i < root.children.length ; ++i)
{
if(external_started)
console.log(root.children[i].toString(), 'is external');
else if(root.children[i]===last_item)
external_started = true;
}
}
}
and
MyElement {
Item {
objectName: 'I am external'
}
}
It's a dirty hack but it works.
I'm saving a reference to the last item in a readonly property called last_item and that will distinguish my last item in qml definition.
Other items which are added outside of the qml file, will be placed after this item in the children list.
I'm trying different approaches to styling a QT's app QML items. My goal is to:
limit the amount of code in the main files (hide all styling stuff in styling files, unlike in the Style Singleton approach)
not have to define every single type of item I'm going to use (unlike in the Custom Component approach)
possibly be able to mix and match different pre-defined styles in a single item.
Maybe there is a clear strategy to get this, I just didn't read about it yet. And maybe it doesn't make any sense anyway :-)
I've been playing with the idea of defining different components, one for each style type I want to define. The idea is to:
- define a component which is going to modify its parent
- insert that component where I want to adopt that specific style
A first approach relies on some javascript calls:
MyStyle.qml:
Item {
Component.onCompleted: {
parent.color = "lightblue"
parent.radius = 5
parent.border.width = 3
parent.border.color = "black"
}
}
And in my main code:
Rectangle {
id: testRectangle
anchors.fill: parent
MyStyle {}
}
This gives me the result I want, but it doesn't feel right:
I'd like for the styling to be applied statically, once and for all
if I start using this all over the place, won't I see artifacts when objects get created, and slow down my interface?
So I tried this too:
MyRectangleStyle.qml:
Item {
property Rectangle styleTarget
styleTarget.color: "lightblue"
styleTarget.radius: 5
styleTarget.border.width: 3
styleTarget.border.color: "black"
}
and in my main code:
Rectangle {
id: testRectangle
anchors.fill: parent
MyStyle {styleTarget: testRectangle}
}
But:
well, it doesn't work :-) (no warnings though, qml simply doesn't load)
and I'm sort of back to having to define every single type of items I'm going to use.
So, is there a better way to achieve what I'm trying to do here? Thanks!
Your second method does not work because your Component sets properties to an item that does not necessarily exist at the time of creating the Component, instead it sets the property when the styleTarget changes. On the other hand, it is not necessary for MyStyle to be an Item since it is not shown, instead use QtObject, and finally to generalize your method change property Item styleTarget toproperty Rectangle styleTarget:
QtObject {
property Item styleTarget
onStyleTargetChanged: {
styleTarget.color = "lightblue"
styleTarget.radius = 5
styleTarget.border.width = 3
styleTarget.border.color= "black"
}
}
I looking into source code of SplitView (%QT_SOURCE_PATH%\qml\QtQuick\Controls\SplitView.qml) and noticed that it used 3 Items to maipulate splitters and items:
Item {
id: contents
visible: false
anchors.fill: parent
}
Item {
id: splitterItems
anchors.fill: parent
}
Item {
id: splitterHandles
anchors.fill: parent
}
According to code, new items is placing into item splitterItems by the function addItem_impl(item). The fuction addItem_impl(item) are called from function init() that pass every child item from Item with id contents. But I wonder how all the children from root item were placed into contents Item?
Via a default property:
default property alias __contents: contents.data
From the documentation:
An object definition can have a single default property. A default property is the property to which a value is assigned if an object is declared within another object's definition without declaring it as a value for a particular property.
[...]
You will notice that child objects can be added to any Item-based type without explicitly adding them to the children property. This is because the default property of Item is its data property, and any items added to this list for an Item are automatically added to its list of children.
Default properties can be useful for reassigning the children of an item. See the TabWidget Example, which uses a default property to automatically reassign children of the TabWidget as children of an inner ListView. See also Extending QML.
This is a simplification of the situation I am dealing with in main.qml file:
Component {
id: component1
property string stringIneedToPass: "Hello"
Text { text: stringIneedToPass }
}
Component {
id: component2
Rectangle {
id: myRectangle
property string stringIneedToReceive = component1.stringIneedToPass; //this doesn't work
}
}
Obviously my situation is more complicated. But in the end I just need to understand how this kind of transfer should be done!
Thank you all!
First of all, a Component element cannot have properties. Components are either loaded from files, or defined declaratively, in the latter case they can contain only one single root element and an id.
Second - you cannot do assignment in the body of an element, only bindings.
Third - you cannot reference properties defined inside an element inside a component from the outside, as that object doesn't exist until the component is instantiated. Such objects can only be referenced from inside.
Other than that, it will work as expected, if you can reference it, you can bind or assign it to a property, depending on what you want.
So you can simply have the string property external:
property string stringIneedToPass: "Hello"
Component {
id: component1
Text {
text: stringIneedToPass
}
}
Component {
id: component2
Rectangle {
id: myRectangle
property string stringIneedToReceive: stringIneedToPass
}
}