I notice that there are two methods by which an event handler can be hooked up to a GWT widget: addHandler and addDomHandler. The JavaDoc for addDomHandler says, "Adds a native event handler to the widget and sinks the corresponding native event. If you do not want to sink the native event, use the generic addHandler method instead."
I'd be very grateful if someone would enlighten me as to the difference between native events and logical events.
Native events are fired directly by the browser - events like clicks, mouseovers, keypresses, etc. To receive those events on a Widget, you have to specifically sink the events.
The generic events are, well, more generic. For example, I've created a SaveEvent and a DeleteEvent for my own use, that get fired when certain UI conditions are met. They are farther away from the browser and would never get fired directly by the browser. I think you should stick with the more generic events when you can. On the other hand, if you're creating a custom widget that you can't make out of other widgets - for example, if you want to build a slider that the user can click and drag - you'll need the DOM events.
Related
I'm just beginning to learn F# and I was wondering how to attach a click event handler to a particular candlestick rendered using the plotly.NET library at https://plotly.net/07_1_candlestick.html
Notice if you scroll down and hover your mouse pointer on a candlestick in one of the sample charts, it pops up with quantitative data for the candlestick.
How can I create a similar click event handler in F# which does some background tasks or creates additional pop-ups/windows for the user to interact with?
I am creating my own GUI in OpenTK.
I want to fire a mouse event when the cursor is, for example, in one of the GUI controls. How can I do that? Because now I'm just iterating through a list of items in the main class, and in the Opentk´s window´s MouseMove event I'm just checking if the mouse coordinates are within the "region" of the component I'm drawing.
This works for now, but I think it could be done in a better way. This way my code is unordered and in the main class, and I would rather have it in the specific component class.
What I would like is to have an event attached to each component of my GUI, so that I can define many events for one component.
I mean, I would like to have for example a button component where I can override or just use a method that fires when an event occurs. Same as OpenGL´s window where you can override events.
This is not a complete answer, because your question is quite broad, but I hope it helps.
In order to implement such a system, here are the core components for a potential design:
UI Components: Some kind of standard interface where different component types can define logic for interactions. Depending on the language, the most common approach is probably something like a parent class Component, with methods to be overridden. These would probably include things like:
Mouse Hover
Mouse Click (press / release)
Click drag
It will also likely need some additional associated information:
Some way to determine the component's location. Could be providing a bounding box, or perhaps a method that tests if a given point is within this component or not.
Information or functionality for drawing the component.
Display and layering settings (is it visible or hidden, should it draw on top of other components or behind).
UI Context: The context is a structure that defines the set of components that are existent in the UI. This could be something like a list structure of Components. In order to build your UI, you would add components to this context. The context will define some behaviour:
Managing components (add / remove / modify).
How to draw the entire context (for example, looping over each component and executing the draw functionality for each).
Handling of events (see next section)
Event Dispatch: To make your UI usable, you can insert an "adapter" layer that handles events from your windowing library (OpenTK) then translates them into usable events for your components and dispatches them. Here is an example of how this might work for a "click" event (pseudo-code):
function TK_Event_ClickPressed(point) {
for component in context {
if component.ContainsPoint(point) {
component.EventClickPressed()
}
}
}
This is actually the more tricky part of the design, in my opinion, because there are some tricky conventions around how component based UI works. You don't necessarily have to follow them, but they're important to be aware of at least because it is probably how people expect your UI to work:
After click press, click drag continues to occur until click release, even if the cursor leaves the component area.
"Actions" occur on click release.
Click release only takes action if the corresponding click press occurred on the same component.
The click release doesn't take any action if the cursor is no longer inside the component (leaving and re-entering the component before release still does the action, though).
You can only be actively clicking one component at a time (the one shown on top), even if multiple components overlap at that spot.
Assuming that you follow these conventions, this means that dispatching events is actually a bit more complicated than just checking if the event point was in a given component or not. You need to maintain some kind of state to keep track of whether the context is currently in a click or not, and which component, if any, is "consuming" the current click. That is, which component should be given the click release and drag events if they occur.
With these systems in place, you just need to create a window, create a UI context, register the adapter layer to the window to act on that context, set up the window to draw the context on frame, then use the context to add / remove / modify components in your program.
Gwt HTML5 Canvas wrapper can responds to mouse and keyboard events, it binds to 5 - 6 types of different events, my question is, it is possible to define entirely new event system such as CanvasEvent (and related handler CanvasEventHandler extends to GwtEvent etc), bind this to canvas object and then handle all events differently using a handler interface methods will be something like onDraw(), onDrag(), onMove(), onSelect() etc.
I dont have good clarity of GWT event system but i want to know is this possible without individuality attaching separate event handlers to form a logic for handling my problem, can I access all possible event as one consolidated object and fire custom event based on conditions. What would be the best way to do it, there are threads with GWT custom events but they include senders, whereas in my case sender is already present (Canvas)
Thanks much
Certainly - remember that all of the GwtEvent objects are completely artificial and are based off of events fired from the native JavaScript. That JavaScript event object, (which comes in via onBrowserEvent) gets wrapped up as a ClickEvent or a KeyDownEvent based on the details of the original object, and then fired off via the internal HandlerManager instance. In the same way, you could listen for a MouseDownEvent, set some state, then if a MouseMoveEvent occurs, fire your own CanvasDrag event. You'd probably stop listening to those move events once a MouseUpEvent happens, then you would issue something like a CanvasDropEvent. If isntead the MouseUpEvent occurred right away with no move, you could trigger a CanvasSelectEvent (or you might have something else in mind for that select event).
Each of these new event types you declare then might contain specifics about whatever is going on. For example, while a MouseMoveEvent just has the element that the mouse is over and the x/y coords, you might be indicating what is being dragged around the page. That might be in the form of the shape that was last clicked, or even the data it represents.
Yes, the 'sender', or source, is already there, but it'll be easier to use if you expose some kind of a method to add handlers like addCanvasDragHandler, etc. This is not required - all users of your code could just use addHandler, but it does make it a little ambiguous about whether or not the widget supports the event in question. You would then call fireEvent on the canvas object to make all handlers of that event type listen.
Or, you could make a new class that contains an internal Canvas widget - possibly a Composite object or just something that implements IsWidget (Canvas has a private constructor, so you can't subclass it). This would enable you to add your own particular handlers, and keep your own HandlerManager/EventBus to track the events you are concerned with.
I have a problem: how can I create gesture event by code, (rotate, magnify or swipe...), I don't want to use it to zoom or rotate a specific image or something like that, I want to create gesture event like scroll event create by CGEventRef cgEvent = CGEventCreateScrollWheelEvent(NULL, kCGScrollEventUnitLine, wheelCount, yScroll, xScroll);
CGEventPost(kCGHIDEventTap, cgEvent);
Thanks
Not all events have "shortcut" creation functions (like CGEventCreateScrollWheelEvent, CGEventCreateMouseEvent, and CGEventCreateKeyboardEvent), so you have to create an empty event and then set the fields manually using the CGEventSet* functions.
The gesture-related events only have public constants for the Cocoa API level. For example, while NSLeftMouseDragged == kCGEventLeftMouseDragged == NX_LMOUSEDRAGGED == 6, NSEventTypeMagnify == 30 doesn't have any equivalent kCGEventMagnify or NX_MAGNIFY.
Also, the way gesture events work is a bit tricky; if you don't send the proper sequence of mouse/trackpad events, gesture, gesture begin/end, and specific-gesture events, it won't work.
There's not much documentation on which fields each event type needs; the easiest way to find out is to first create an event tap that logs everything, then generate the events you want and see what gets logged. In fact, you probably want to also log an NSEvent global monitor (log both the NSEvent itself and its underlying cgEvent).
What is the best solution to implement mouse or load or select event in prism 4. I am adding double click event on dxgrid and looking for a best practice to implement this feature.
for eg : mouse click, loaded, selected
Thanks,
You would typically use Behaviors for that. Behaviors map specific events of your View to commands in your ViewModel.