Representing an Event as an Object in Java

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143 Representing an Event as an Object
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occurredTable 142 describes the important properties and methods of the event object
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Table 142
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Summary: Property: target Property: currentTarget
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Dojo Event Object
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The Dojo event object provides an object wrapper around the event exposing its important properties and methods DOM node on which the event was triggered DOM node that is assigned to act as the target DOM node for the event object It is usually the same as the target node but may be assigned to a different node by Dojo This is the element you should reference in event handler code This is the X coordinate of the cursor relative to currentTarget DOM element This is the Y coordinate of the cursor relative to currentTarget DOM element This is the X coordinate of the cursor relative to the viewport at the time the event was created The viewport is the area in the browser in which the document content is viewed This doesn t include sidebar menus or status lines It is the space that is available to the page
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Property: layerX Property: layerY Property: pageX
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Property: pageY Property: type Property: relatedTarget
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This is the Y coordinate of the cursor relative to the viewport at the time the event was created The name of the event such as click or mouseover This string will not have on at the beginning For certain events such as onmouseover and onmouseout this property references the object that the mouse moved from This would be different than the DOM element on which the event was triggered Contains the keycode for key press events The JavaScript event model allows event processing to bubble up to overlapping DOM elements In other words, the same event is triggered on the parent element Running this function stops that from happening Some DOM events have a default behavior (such as a submit button submitting the form) Running this method on an event prevents the default behavior from occurring
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Property: charCode Function: stopPropagation
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Function: preventDefault
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14
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Events and Event Handling
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144 Using Aspect Oriented Programming in Dojo
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Aspect Oriented Programming (AOP) is a programming technique available in some languages that allows certain types of program execution to be treated as events to which event handlers may be applied For example, let s define two functions, foo and bar, which simply write a message to the console as shown in the following code:
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function foo() { consolelog("Running foo"); } function bar() { consolelog("Running bar"); }
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Now we need to make sure that every time foo executes, bar is also executed A simple way to do this is to add a line of code to the foo method that executes bar, as shown here:
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function foo() { consolelog("Running foo"); bar(); }
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Although the solution just provided would work, we ve hard-coded itWhat if we wanted to make this assignment dynamic Dojo provides a solution Dojo can treat the execution of a function as an event to which we can associate another function as an event handlerThe following version of dojoconnect provides this association:
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dojoconnect(null, "foo", null, "bar");
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Now whenever we run foo, the function bar automatically runs next We ve now implemented a simple example of AOP But if you re new to AOP, you may be asking:Why in the world would I want to do this The standard usage of this approach allows us to dynamically add features that apply to many object types For example, if we wanted to add logging to functions, we could do it after the functions were already written by assigning a log method to each of the functions using AOP instead of having to add code to each function The AOP approach can be better because it doesn t hard code the logging method to the target factions and no target function code has to be modified After all, if you believe the industry benchmarks, every time you touch code, there is a 5% chance that you will break something So if you can avoid modifying the methods, you re better off