I have two aspxcallbackpanels with two different callback functions. Is there a way to check on Page_Load which one of them is being executed?
Analyze the ASPxCallbackInstance.IsCallback property to determine whether or not a particular callback control is in the callback mode.
Related
I am developing a quick app and I am having a problem while calling method below.
device.getInfo()
I am trying to obtain my phone's height from the information provided but it always returns 0.
Any suggestions?
Please check whether the asynchronous mode is used when the device.getInfo() method is invoked in the onCreate() method in the app.ux file. If so, delete the asynchronous mode.
After the asynchronous mode is deleted, if the height is still 0, the device.getInfo() method may be invoked before the data is ready. It usually takes around 50-100 ms for the data to be ready.
I could not find my answer in this thread:
Using the GWT Scheduler
The GWT Scheduler class has scheduleDeferred API which executes after the browser event loop returns. The scheduleFinally API allows me to execute code before the control returns to the browser event loop.
How do I decide whether I should use scheduleDeferred or scheduleFinally? Is there a code example which shows the difference in behavior?
To understand this, you need to first get the basic idea of an event loop. When you write code to run in the browser, you don't write this loop - it lives in the browser, waiting for the user to do something. When that something happens (mouse event, keyboard event, AJAX call returns, setTimeout goes off), the loop calls into your code, and lets you handle it however you would like to.
So first, we have scheduleDeferred, which is a way to notify the browser that we have some code to run soon, but not in this loop. This is a handy way to let the browser regain control, render some content, and then give you control again. This can be helpful to break up calculations into several chunks to avoid any "long running script" errors, or can be an early attempt at animation (Note: use the actual requestAnimationFrame api from the browser, or AnimationScheduler.get().requestAnimationFrame in GWT instead for this).
Next, there are two interesting places in the loop where you might have code that you would like to run - either right as the browser transfers control to you, or right before you return control back again. Of these two, the end is usually more interesting: scheduleFinally. This lets you run some code inside the current event loop, but not until the very end of it. CssResource uses this strategy in its ensureInjected() method - when you run several different calls to this method, rather than poking the DOM several times, it batches them all up and runs them at the end of the event loop, using scheduleFinally.
The last one, the beginning of each event loop is managed by another method - scheduleEntry. In theory, this could be used in conjunction with finally to reimplement a simple version of AngularJS's binding wiring.
//event comes in to GWT from the $entry method, and follows these steps
try {
// 1. run registered scheduleEntry calls
// 2. run the current event or callback that the browser called us for
} finally {
// 3. run registered scheduleFinally calls
}
Any call to scheduleDeferred during those steps has added a call to the next event loop, to run as part of #2.
I am using GWT. In my client side code I am calling service method. With that method i am getting values from database and with that values I am performing some logical operation. What happened is in success method until it completed rest of the code in outer than service method executing. How to block execution code until my success method completes?
Thanks in advance
Move the rest of your code into your success method. If there are many lines then extract them into some new method and just call this method as a last instruction from your success method.
You can either put the "conditional" code in a separate method and call that method in the Receiver#onSuccess() method
Don't forget to implement the onFailure() method to notify the user so doesn't remain waiting infront of his screen.
If your conditional code is application wide, use the EventBus to notify the application components that they can do the job.
I'm very new on iOS application development so please explain me about delegate and call back. When we use use call back and delegate?
Call backs are used to allow an API or service to provide information to your code when certain events occur (e.g. when a task has completed). This is useful in asynchronous programming, e.g. when you want your current thread to get on with something else, or to allow the user to continue using the UI. (i.e. a call back is a function or lambda you have written, which is passed as a parameter to another method)
A delegate is the 'signature' (the 'type definition' of a method, including parameters) that a method (such as a call back) must provide in order for it to be useable as callback or event handler.
Edit Just to be complete, Delegation is also a design pattern, whereby the responsibility of control or action is delegated from one object to another.
Big piece about delegates here on the dev centre:
http://developer.apple.com/library/ios/#DOCUMENTATION/Cocoa/Conceptual/CocoaFundamentals/CommunicatingWithObjects/CommunicateWithObjects.html
There is a tutorial app using callback/delegate
http://brandontreb.com/objective-c-programming-tutorial-creating-a-twitter-client-part-1/
No offense, but I may be asking a strange question. I am a beginner, learning advanced OOP, and confused about a few concepts. Coming to the point. It may be ridiculous. But can someone tell me exactly and correctly what does callback literary mean? And how it differs from a proxy class in C++ which we use for information hiding. Apologies in advance, if I missused the terminology.
From Wikipedia:
A callback is a reference to executable code, or a piece of executable code, that is passed as an argument to other code.
As for proxy classes, see this question.
It's two different things. An instance of a proxy class can be used as callback, but that's about the only relation I can see between them.
The idea of a call back is to start some action then do something else until the action completes.
An example from the real world is to telephone the plumber for a repair. The plumber says they are currently at a work site and unable to see their schedule for the next day right now. However the plumber says that they will be in the office later and will be able to check their schedule. The plumber then promises to give you a call back once they are in the office and able to check the schedule. You could then either sit down next to the telephone and wait for the return telephone call (blocking call back) or read a book or paint the house until the plumber calls back (deferred call back).
In C, a callback function is a function body that is specified as a callback. The address of the function, a function pointer, is provided to the function being called to perform some kind of action. When the action is completed the callback function is invoked to do something, usually some form of cleanup and/or notification.
Normally a callback is used when a function is called to start some action and then returns immediately to the caller before the action completes and its result is known. The callback is used as a way to notify the result of the action when the started action is completed.
Another form of callback is to register a function for an event so that when the event happens, the function will be called to do something. So you might specify a callback for when a mouse click event is received.
A proxy class is a class that acts as an interface for a class. You could think of a proxy class as being similar to a stunt double who does the dangerous things for an actor. Or a proxy for a share holder's meeting is a person or organization who stands in for the actual share holder to perform specific duties for the share holder.
A callback is not a proxy though a callback may be used by a proxy as part of the functionality required to do its proxy duties.