how to print barcode in asp net c# THE IMAGE GALLERY REVISITED in Font

Make Quick Response Code in Font THE IMAGE GALLERY REVISITED

CHAPTER 6 THE IMAGE GALLERY REVISITED
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There is one last piece of fine-tuning that often arises with any scripts that are attached to the onclick event handler. Take a look at the heart of the prepareGallery function: links[i].onclick = function() { if (showPic(this)) { return false; } else { return true; } } First, for brevity in the examples, let's change this to use the ternary operator instead: links[i].onclick = function() { return showPic(this) false : true; } This works fine. When the link is clicked, the showPic function is executed. It looks like I m assuming that the user will be clicking on the link with a mouse. But remember, not everybody navigates using a mouse. People with visual disabilities, for example, aren t going to move a small icon around their screen. Instead, they are likely to navigate using a keyboard. You don t need a mouse to browse the web. You can use the Tab key on your keyboard to move from link to link. Pressing the Return key will activate the currently selected link. There is an event handler specifically for the action of pressing any key on the keyboard. It is called onkeypress. If I want to execute the same behavior for onkeypress as onclick, I could simply duplicate the instructions: links[i].onclick = function() { return showPic(this) false : true; } links[i].onkeypress = function() { return showPic(this) false : true; } There s an easier way to ensure that onkeypress imitates onclick, however: links[i].onkeypress = links[i].onclick; This assigns all the functionality from the onclick event to the onkeypress event as well: links[i].onclick = function() { return showPic(this) false : true; } links[i].onkeypress = links[i].onclick; That brings us right back to the benefits of unobtrusive JavaScript. By keeping all your functions and event handlers in external files, you can change them without tinkering with the markup. You can always revisit your scripts and refine them, knowing that those refinements will automatically be applied to every web page that references the JavaScript file.
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CHAPTER 6 THE IMAGE GALLERY REVISITED
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If I were still using inline event handlers, I would have needed to make a lot of changes to my markup as the JavaScript functionality changed. I used to have inline event handlers like this: <li> <a href="images/fireworks.jpg" onclick="showPic(this);return false;"title="A fireworks display">Fireworks</a> </li> When I changed the showPic function to return either true or false, I would have needed to update the event handlers accordingly: <li> <a href="images/fireworks.jpg" onclick="return showPic(this) false : true;" title="A fireworks display">Fireworks</a> </li> If my image gallery were more than a few links long, this would have been quite tiresome. Suppose I wanted to add the onkeypress event handler. I would have to go through all the links and add another inline event handler to each one: <li> <a href="images/fireworks.jpg" onclick="return showPic(this) false : true;" onkeypress="return showPic(this) false : true;" title="A fireworks display">Fireworks</a> </li> That would have been a lot of drudgery. It s so much simpler to tweak and adjust a few lines of JavaScript in an external file.
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As it turns out, I m not going to add the onkeypress event handler at all. This event handler is quite problematic. It is triggered whenever a key is pressed. In some browsers, that includes the Tab key! That means that a user navigating with a keyboard can never tab past a link if a function associated with onkeypress returns false. That s exactly what s happening with the image gallery. The showPic function, if it is successful, returns false. So where does that leave users navigating with a keyboard Fortunately, the onclick event handler turns out to be smarter than it sounds. With a name like onclick, it gives the impression of being tied to the action of clicking a button on a mouse. In fact, in nearly all browsers, the onclick event handler is also triggered if you press Return while tabbing from link to link. It would be more accurate if it were named something like onactivate. There is a lot of confusion surrounding onclick and onkeypress, which is hardly surprising given the terminology. Some accessibility guidelines recommend using onkeypress whenever you use onclick. In reality, this could cause more harm than good. Avoid using onkeypress. The onclick event handler is all that s needed. In spite of its name, onclick supports keyboard access perfectly well. The finished functions look like this: function prepareGallery() { if (!document.getElementsByTagName) return false; if (!document.getElementById) return false; if (!document.getElementById("imagegallery")) return false; var gallery = document.getElementById("imagegallery"); var links = gallery.getElementsByTagName("a"); for ( var i=0; i < links.length; i++) {
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