Signal and Slots with QML confusion with QML items

[technoViking]

Hi,

I was wondering if anyone can explain how SIgnals and Slots work in QML.

I understand them in Qt.

So if I have 2 files.
A.qml

B.qml


I want A.qml to send a signal to B.qml

The signal I want A to send to B is a string.

//A.qml

Item
{
   id: aItem
 
 
signal sendStringSignal
 
   Rectangle
  {
      onClicked: {    //need to send a to B.qml  }
 
  }
 
}

Item
{
   id: aItem


signal sendStringSignal

   Rectangle
  {
      onClicked: {    //need to send a to B.qml  }

  }

}

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I wasn't able to find code snippets of anyone doing this, any ideas?

Thanks

[somnathbanik]

Hi,

I was wondering if anyone can explain how SIgnals and Slots work in QML.

I understand them in Qt.

So if I have 2 files.
A.qml

B.qml


I want A.qml to send a signal to B.qml

The signal I want A to send to B is a string.

//A.qml

Item
{
   id: aItem
 
 
signal sendStringSignal
 
   Rectangle
  {
      onClicked: {    //need to send a to B.qml  }
 
  }
 
}

Item
{
   id: aItem


signal sendStringSignal

   Rectangle
  {
      onClicked: {    //need to send a to B.qml  }

  }

}

To copy to clipboard, switch view to plain text mode 

I wasn't able to find code snippets of anyone doing this, any ideas?

Thanks

Rectangle {

onClicked: { container.clicked(); }
}

[technoViking]

Thanks so that seems to be sending a clicked() signal but I don't see how you can send a string through that signal and how does the other .qml file accept that signal, aka how does it make a slot to receive the string?

[somnathbanik]

Thanks so that seems to be sending a clicked() signal but I don't see how you can send a string through that signal and how does the other .qml file accept that signal, aka how does it make a slot to receive the string?

Please refer to the example C:\Qt\4.7.0\demos\declarative\flickr. it has got everything, hope this will help you.

[wysota]

Thanks so that seems to be sending a clicked() signal but I don't see how you can send a string through that signal and how does the other .qml file accept that signal, aka how does it make a slot to receive the string?

In QtQuick you usually use property binding which is a higher-level mechanism than signals and slots (and it uses signals under the hood in case of C++ code). Most of the times signals are used as notification of some property changes and all you need to do is to follow this pattern - you declare a property in one object and write a statement in the other object that uses the name of the property defined earlier.

Here is a dirty example:

import Qt 4.7
 
Rectangle {
  id: win
  width: 200 
  height: 200
 
  TextInput {
    anchors.top: win.top; anchors.left: win.left; anchors.right: win.right;
    id: objectA
    text: "xyz"
    height: 100
  }
 
  Text {
    id: objectB
    anchors.bottom: win.bottom; anchors.left: win.left; anchors.right: win.right;
    height: 100
    text: "=>"+objectA.text+"<="
  }
}

import Qt 4.7

Rectangle {
  id: win
  width: 200 
  height: 200

  TextInput {
    anchors.top: win.top; anchors.left: win.left; anchors.right: win.right;
    id: objectA
    text: "xyz"
    height: 100
  }

  Text {
    id: objectB
    anchors.bottom: win.bottom; anchors.left: win.left; anchors.right: win.right;
    height: 100
    text: "=>"+objectA.text+"<="
  }
}

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Try changing the text of the first object and see what happens.

Remember QML is a declarative language. You declare text of objectB to be the text of objectA surrounded by arrows.

[technoViking]

I see, I didn't realize that's the proper way of doing things. It seems like that would make a ton of global objects, and everyone is simply modifying the global objects

[wysota]

I see, I didn't realize that's the proper way of doing things.

It's not a "proper" way, it's one of the ways that is more declarative than using signals and slots directly (which is imperative).

It seems like that would make a ton of global objects, and everyone is simply modifying the global objects

You don't need to modify any global objects, you can create a local alias to a property of another object. Or maybe I don't understand what you mean by those global objects... hmm...

It would be best if you explained what do you need all this for and maybe then we'll be able to find a solution tailored for the specific situation.

[technoViking]

Thanks for the response. I will get a better description in a few!