how to print barcode in vb.net 2008 A touching example: the event reporter in Objective-C

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A touching example: the event reporter
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nextResponder may not know about the manageTouches method, but it will; you can
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ignore this warning. You ll see some other ways to use the nextResponder method toward the end of our discussion of events.
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Controlling your events
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Intercepting touches and forwarding them up to the view controller may be the toughest part of this code. After the events get to the view controller, they run through a simple method called manageTouches:, as shown in listing 6.1.
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Listing 6.1
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manageTouches, which accepts inputs and changes views
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/*eventreporterViewController.m*/ - (void)manageTouches:(NSSet *)touches { for (UITouch *touch in touches) { if (touch.phase == UITouchPhaseBegan) { CGPoint touchPos = [touch locationInView:self.view]; startField.center = touchPos; startField.text = [NSString stringWithFormat: @"Begin: %3.0f,%3.0f",touchPos.x,touchPos.y]; } else if (touch.phase == UITouchPhaseMoved) { bottomLabel.text = @"Touch is moving ..."; } else if (touch.phase == UITouchPhaseEnded) { if (touch.tapCount > 1) { bottomLabel.text = [NSString stringWithFormat: @"Taps: %2i",touch.tapCount]; } else { bottomLabel.text = [NSString string]; } CGPoint touchPos = [touch locationInView:self.view]; endField.center = touchPos; endField.text = [NSString stringWithFormat: @"End: %3.0f,%3.0f",touchPos.x,touchPos.y]; } } }
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Determines touch phase
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Touches are sent as an NSSet, which can be broken apart in a number of ways, as described in the NSSet class reference. Here, you use a simple for ... in construction that lets you look at each touch in turn. When you get a touch, the first thing you do is determine what phase it arrived in. Originally, you could have determined this information based on which method a touch arrived through; but because you combined everything you have to fall back on the phase property. Fortunately, it s easy to use. You match it up to one of three constants B, and that determines which individual actions your program undertakes. Having different responses based on the phase in which a touch arrives is common which is why the event methods are split up in the first place. The example demonstrates this with some distinct responses: you move your start field when touches begin, you move your end field when touches end, and you update the bottom label in both the moved and ended phases.
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Monitoring events and actions
In the UITouchPhaseBegan response, you delve further into your touches data by using the locationInView: method to figure out the precise coordinates where a touch occurred. You re then able to use that data to reposition your text field and to report the coordinates in the text field. You later do the same thing in the UITouchPhaseEnded response. Finally, you look at the tapCount in the UITouchPhaseEnded response. This is generally the best place to look at taps because the device now knows that the user s finger has come off the screen. As you can see, it s easy to both run a command based on the number of taps and to report that information. Figure 6.5 shows the event responder in action. Imagine a finger that touches down on the space where the Begin text field is and that is currently moving across the screen. And with that, your event reporter is complete. In addition to illustrating how a program can respond to touches, we ve highlighted how the MVC model can be used in a real application. The project contains four views: a reportView, a UILabel, and two UITextFields. It s tempting to process events in the reportView, especially because you had to create a subclass anyway; but instead you pushed the events up to the view controller and in doing so revealed why you want to do MVC modeling. Because it takes on the controller role, you give the view controller access to all of its individual objects, and therefore you don t have to try to remember what object
Figure 6.5 Your event responder uses a few graphical elements to report events as they occur.
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Other event functionality
knows about what other object. Tying things into the view controller, rather than scattering them randomly across your code, makes the project that much more readable and reusable, which is what most architectural and design patterns are about.
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