IOS View Programming Guide notes

<span id="Label3"></p>The program that we see<p><p>For all iOS apps, what we're looking at is UIVIEW.</p></p><p><p>UIView such as scenes, UIWindow such as stage, UIView in the UIWindow stage, so that we see a colorful interface Ui. UIWindow itself does not have any content, it only provides a place to let these uiview to display, Switch.</p></p><p><p>typically, an app has only one UIWindow as the display, and multiple UIWindow are used when we want to display multiple Screens.</p></p>The basic structure of UIView<p><p>1, UIView attached to the uiwindow, only on the UIWindow on the view, we can See.</p></p><p><p>2, UIView itself can be used as a container to display and manage subview, make the interface richer.</p></p><p><p>3, each uiview has a corresponding core Animation layer class object for Support. The Layer class object is generally a Calayer class Object. This object stores some of the information data corresponding to the UIView object and handles the animation operations of the UIVIEW.</p></p><p><p>With the Calayer object, the main functions are as Follows:</p></p><p><p>(1) the Calayer object stores the information data corresponding to the UIView object, which can greatly reduce the number of UIView rendered, and we can read the stored data in the Calayer object as much as possible, without having to render the UIView every Time.</p></p><p><p>(2) It is precisely because the Calayer object stores the information of UIView that the current contents of UIView can be manipulated, and the animation effect of UIView is Realized.</p></p><p><p>(3) we can achieve richer and more flexible display and animation effects by directly manipulating Calayer Objects.</p></p><p><p>uiwindow, UIView, Core Animation Layer object relationships are as Follows:</p></p><p><p><br></p></p>View hierarchy and Subview management<p><p>As mentioned earlier, UIView can add a child view to form a parent-child logical relationship such as Superview,subview.</p></p><p><p>Subview is managed by the parent view in a Sub-view Queue.</p></p>Hierarchical relationship of view display<p><p>The last view that is added masks the previous view.</p></p>Incident response Chain (event<span style="font-family:‘Lucida Grande‘,‘Lucida Sans Unicode‘,Helvetica,Arial,Verdana,sans-serif; font-size:13px"><span style="font-family:‘Lucida Grande‘,‘Lucida Sans Unicode‘,Helvetica,Arial,Verdana,sans-serif; font-size:13px">Responder Chain</span></span>）<p><p>When the app obtains the User's action event, The event is first passed to the Subview at the top of the occurrence, and if the Subview does not respond to the event, it is passed to the superview of the view in response, so it continues to pass. Until the event is responded to or discarded by the program until it is Processed. This is called the event <span style="font-family:‘Lucida Grande‘,‘Lucida Sans Unicode‘,Helvetica,Arial,Verdana,sans-serif; font-size:13px">responder Chain. </span></p></p><p><p><span style="font-family:‘Lucida Grande‘,‘Lucida Sans Unicode‘,Helvetica,Arial,Verdana,sans-serif; font-size:13px"><br></span></p></p><span style="font-family:‘Lucida Grande‘,‘Lucida Sans Unicode‘,Helvetica,Arial,Verdana,sans-serif"><span style="font-family:‘Lucida Grande‘,‘Lucida Sans Unicode‘,Helvetica,Arial,Verdana,sans-serif"><span style="font-size:24px">content drawing period for view</span></span></span><p><p><span style="font-family:‘Lucida Grande‘,‘Lucida Sans Unicode‘,Helvetica,Arial,Verdana,sans-serif; font-size:13px">In ios, the UIView class takes an <span style="color:#ff0000">On-demand strategy</span> to draw the display of the VIEW. An on-demand strategy means that the system will call your drawing function to redraw the view only if you explicitly tell the system that it needs to redraw the view, otherwise, in most cases, only the View's <span style="color:#ff6666">content snapshot image</span> will be used instead of the View's content display.</span></p></p><p><p><span style="font-family:‘Lucida Grande‘,‘Lucida Sans Unicode‘,Helvetica,Arial,Verdana,sans-serif; font-size:13px">The specific implementation is as Follows:</span></p></p><p><p><span style="font-family:‘Lucida Grande‘,‘Lucida Sans Unicode‘,Helvetica,Arial,Verdana,sans-serif; font-size:13px">1, When a view is displayed on the screen for the first time, the system automatically calls the View's drawing function, completes the content display, and retains a snapshot image for the Content.</span></p></p><p><p><span style="font-family:‘Lucida Grande‘,‘Lucida Sans Unicode‘,Helvetica,Arial,Verdana,sans-serif; font-size:13px">2, if the content of the view does not change, in most cases, the system uses only snapshot images to represent the view Content. Note here that the system does not proactively ask if the content of the view has changed, and you need to proactively notify the system that the content has changed to update the view display Content.</span></p></p><p><p><span style="font-family:‘Lucida Grande‘,‘Lucida Sans Unicode‘,Helvetica,Arial,Verdana,sans-serif; font-size:13px">3. When you make a change to the content of the view, call</span></p></p><p><p><span style="font-family:‘Lucida Grande‘,‘Lucida Sans Unicode‘,Helvetica,Arial,Verdana,sans-serif; font-size:13px"><span style="font-family:‘Lucida Grande‘,‘Lucida Sans Unicode‘,Helvetica,Arial,Verdana,sans-serif; font-size:13px"></span> <code style="font-size:13px; font-family:Courier,Consolas,monospace; color:rgb(102,102,102)">setNeedsDisplay</code> <span style="font-family:‘Lucida Grande‘,‘Lucida Sans Unicode‘,Helvetica,Arial,Verdana,sans-serif; font-size:13px">or</span><code style="font-size:13px; font-family:Courier,Consolas,monospace; color:rgb(102,102,102)">setNeedsDisplayInRect:</code><br></span></p></p><p><p><span style="font-family:‘Lucida Grande‘,‘Lucida Sans Unicode‘,Helvetica,Arial,Verdana,sans-serif; font-size:13px">Method notifies the system that the content has changed and needs to redraw the view Interface.</span></p></p><p><p><span style="font-family:‘Lucida Grande‘,‘Lucida Sans Unicode‘,Helvetica,Arial,Verdana,sans-serif; font-size:13px">4, the system learned that the content has changed, will not immediately redraw the view interface, but when the end of the run loop, ready to redraw the content, will change the content of the view to REDRAW.</span></p></p><p><p><span style="font-family:‘Lucida Grande‘,‘Lucida Sans Unicode‘,Helvetica,Arial,Verdana,sans-serif; font-size:13px">5. When the system redraws the view, the process is not uniform. For custom view, we need to rewrite</span></p></p><p><p><span style="font-family:‘Lucida Grande‘,‘Lucida Sans Unicode‘,Helvetica,Arial,Verdana,sans-serif; font-size:13px">Drawrect: Method.<br></span></p></p><p><p><span style="font-family:‘Lucida Grande‘,‘Lucida Sans Unicode‘,Helvetica,Arial,Verdana,sans-serif; font-size:13px">of course, You can also change the View's content by changing the View's layer object directly.</span></p></p><p><p><span style="font-family:‘Lucida Grande‘,‘Lucida Sans Unicode‘,Helvetica,Arial,Verdana,sans-serif; font-size:13px">6. When the system finishes redrawing the view, a new snapshot of the content is collected to represent the View's content as a view display for most of the Time.</span></p></p><p><p><span style="font-family:‘Lucida Grande‘,‘Lucida Sans Unicode‘,Helvetica,Arial,Verdana,sans-serif; font-size:13px">Note that the geometric deformation of a general view, such as a small stretch, does not cause a redraw of the content, but only a small stretch of the content Snapshot.</span></p></p><p><p><span style="font-family:‘Lucida Grande‘,‘Lucida Sans Unicode‘,Helvetica,Arial,Verdana,sans-serif; font-size:13px"><br></span></p></p><p><p><span style="font-family:‘Lucida Grande‘,‘Lucida Sans Unicode‘,Helvetica,Arial,Verdana,sans-serif; font-size:13px">Content mode for view</span></p></p><p><p><span style="font-family:Lucida Grande,Lucida Sans Unicode,Helvetica,Arial,Verdana,sans-serif; font-size:12px">As mentioned earlier, when the view is displayed on the screen, a snapshot is used instead of the representation Content.</span></p></p><p><p><span style="font-family:Lucida Grande,Lucida Sans Unicode,Helvetica,Arial,Verdana,sans-serif; font-size:12px">This is what happens when we change the properties of a View's frame, its contents (the content Snapshot) do not necessarily change at the same time. The way content is displayed depends on the contents <span class="content_text" style="margin-top:0px; font-size:13px; font-family:‘Lucida Grande‘,‘Lucida Sans Unicode‘,Helvetica,Arial,Verdana,sans-serif; margin-bottom:0.833em; padding-bottom:0.833em">Modes</span>of the UIView object<span style="font-family:‘Lucida Grande‘,‘Lucida Sans Unicode‘,Helvetica,Arial,Verdana,sans-serif; font-size:13px">. The default system takes Uiviewcontentmodescaletofill mode to fill the content snapshot with the entire view Area. Several forms of the Content mode are as Follows:</span></span></p></p><p><p><span style="font-family:Lucida Grande,Lucida Sans Unicode,Helvetica,Arial,Verdana,sans-serif; font-size:12px"><span style="font-family:‘Lucida Grande‘,‘Lucida Sans Unicode‘,Helvetica,Arial,Verdana,sans-serif; font-size:13px"><br></span></span></p></p><p><p><span style="font-family:‘Lucida Grande‘,‘Lucida Sans Unicode‘,Helvetica,Arial,Verdana,sans-serif; font-size:13px"><br></span></p></p><p><p><span style="font-family:‘Lucida Grande‘,‘Lucida Sans Unicode‘,Helvetica,Arial,Verdana,sans-serif"><span style="font-size:12px">Note that when you set the Contentmode of a view, the geometric deformation of each view causes the system to call the View's</span> <span style="font-size:13px; color:rgb(102,102,102); font-family:Courier,Consolas,monospace">drawrect:</span> <span style="font-family:Courier,Consolas,monospace"><span style="font-size:12px; color:#333333">method to redraw the view, so you should avoid using this property, and for system view, we should never use Attributes. </span></span></span></p></p><span style="font-family:‘Lucida Grande‘,‘Lucida Sans Unicode‘,Helvetica,Arial,Verdana,sans-serif"><span style="font-family:‘Lucida Grande‘,‘Lucida Sans Unicode‘,Helvetica,Arial,Verdana,sans-serif"><span style="font-family:Courier,Consolas,monospace"><span style="font-size:24px; color:#333333">the coordinate system of the view</span></span></span></span><p><p><span style="font-family:‘Lucida Grande‘,‘Lucida Sans Unicode‘,Helvetica,Arial,Verdana,sans-serif"><span style="font-family:Courier,Consolas,monospace"><span style="font-size:12px; color:#333333">The coordinate system of the iOS system is as Follows:</span></span></span></p></p><p><p><span style="font-family:‘Lucida Grande‘,‘Lucida Sans Unicode‘,Helvetica,Arial,Verdana,sans-serif"><span style="font-family:Courier,Consolas,monospace"><span style="font-size:12px; color:#333333"><br></span></span></span></p></p><p><p><span style="font-family:‘Lucida Grande‘,‘Lucida Sans Unicode‘,Helvetica,Arial,Verdana,sans-serif"><span style="font-family:Courier,Consolas,monospace"><span style="font-size:12px; color:#333333"><br></span></span></span></p></p><p><p><span style="font-family:‘Lucida Grande‘,‘Lucida Sans Unicode‘,Helvetica,Arial,Verdana,sans-serif"><span style="font-family:Courier,Consolas,monospace"><span style="font-size:12px; color:#333333">uiwindow, UIView all have their own coordinate system. For UIView Common Properties frame,bound,center their properties are relative to the different coordinate systems. Specific as Follows:</span></span></span></p></p><p><p><span style="font-family:‘Lucida Grande‘,‘Lucida Sans Unicode‘,Helvetica,Arial,Verdana,sans-serif"><span style="font-family:Courier,Consolas,monospace"><span style="font-size:12px; color:#333333"></span></span></span></p></p><p style="margin-top:0px; margin-bottom:0.833em; font-size:13px; font-family:‘Lucida Grande‘,‘Lucida Sans Unicode‘,Helvetica,Arial,Verdana,sans-serif"><p style="margin-top:0px; margin-bottom:0.833em; font-size:13px; font-family:‘Lucida Grande‘,‘Lucida Sans Unicode‘,Helvetica,Arial,Verdana,sans-serif">A View object tracks its size and location using its <code style="font-family:Courier,Consolas,monospace; color:rgb(102,102,102)">frame</code> , <code style="font-family:Courier,Consolas,monospace; color:rgb(102,102,102)">bounds</code> and <code style="font-family:Courier,Consolas,monospace; color:rgb(102,102,102)">center</code> <span class="pediaLink">properties</span>:</p></p> <ul class="ul" style="list-style-position:outside; margin:0px 0px 0.833em 1.35em; padding:0px 0px 0.5em; font-family:‘Lucida Grande‘,‘Lucida Sans Unicode‘,Helvetica,Arial,Verdana,sans-serif; font-size:13px"> <li class="li" style="margin-top:0.583em"><li class="li" style="margin-top:0.583em"><p style="margin-top:0.667em; margin-bottom:0.833em; display:inline"><code style="font-family:Courier,Consolas,monospace; color:rgb(102,102,102)">frame</code>The property contains the <span class="newTerm" style="font-style:italic">frame rectangle</span>, which specifies the size and location of the view in its Supervi EW ' s coordinate system.</p></li></li> <li class="li" style="margin-top:0.583em"><li class="li" style="margin-top:0.583em"><p style="margin-top:0.667em; margin-bottom:0.833em; display:inline"><code style="font-family:Courier,Consolas,monospace; color:rgb(102,102,102)">bounds</code>The property contains the <span class="newTerm" style="font-style:italic">bounds rectangle</span>, which specifies the size of the view (and its content Origin) I n The view ' s own local coordinate system.</p></li></li> <li class="li" style="margin-top:0.583em"><li class="li" style="margin-top:0.583em"><p style="margin-top:0.667em; margin-bottom:0.833em; display:inline">The property contains the known center point of the view in the <code style="font-family:Courier,Consolas,monospace; color:rgb(102,102,102)">center</code> Superview ' s coordinate system.</p></li></li> </ul><span style="font-family:Lucida Grande,Lucida Sans Unicode,Helvetica,Arial,Verdana,sans-serif; font-size:12px"><span style="font-family:Lucida Grande,Lucida Sans Unicode,Helvetica,Arial,Verdana,sans-serif; font-size:12px">to summarize, It is the Frame,center property of the view whose coordinate system is for its superview coordinate system. The bounds property, however, is for its own coordinate system. </span></span><span style="font-family:Lucida Grande,Lucida Sans Unicode,Helvetica,Arial,Verdana,sans-serif; font-size:12px"><span style="font-family:Lucida Grande,Lucida Sans Unicode,Helvetica,Arial,Verdana,sans-serif; font-size:12px"><br></span></span><span style="font-family:Lucida Grande,Lucida Sans Unicode,Helvetica,Arial,Verdana,sans-serif; font-size:12px"><span style="font-family:Lucida Grande,Lucida Sans Unicode,Helvetica,Arial,Verdana,sans-serif; font-size:12px">Frame, Center, Bounds Relationships</span></span><span style="font-family:Lucida Grande,Lucida Sans Unicode,Helvetica,Arial,Verdana,sans-serif; font-size:12px"><span style="font-family:Lucida Grande,Lucida Sans Unicode,Helvetica,Arial,Verdana,sans-serif; font-size:12px">Frame,center are relative to the Superview coordinate system of the view, so they can be used as subview in the Superview position and Size. For displacement motion, It is recommended to change the center property, because the frame property does not exist in some variants. </span></span><span style="font-family:Lucida Grande,Lucida Sans Unicode,Helvetica,Arial,Verdana,sans-serif; font-size:12px"><span style="font-family:Lucida Grande,Lucida Sans Unicode,Helvetica,Arial,Verdana,sans-serif; font-size:12px">frame,center,bounds affect each other, specifically as Follows:</span></span><span style="font-family:Lucida Grande,Lucida Sans Unicode,Helvetica,Arial,Verdana,sans-serif; font-size:12px"><span style="font-family:Lucida Grande,Lucida Sans Unicode,Helvetica,Arial,Verdana,sans-serif; font-size:12px"></span></span> <ul class="ul" style="list-style-position:outside; margin:0px 0px 0.833em 1.35em; padding:0px 0px 0.5em; font-family:‘Lucida Grande‘,‘Lucida Sans Unicode‘,Helvetica,Arial,Verdana,sans-serif; font-size:13px"> <li class="li" style="margin-top:0.583em"><li class="li" style="margin-top:0.583em"><p style="margin-top:0.667em; margin-bottom:0.833em; display:inline">When You set The <code style="font-family:courier,consolas,monospace; color:rgb (102,102,102)">frame </code>   property, the size of value in The <code style="font-family:courier,consolas,monospace; Color:rgb (102,102,102)" bounds < code>  property changes to match the new size of the frame Rectangle. The value in The <code style="font-family:courier,consolas,monospace; color:rgb (102,102,102)">center </code>  property similarly changes to match the new center point of the frame rectangle. </code></p><code style="font-family:courier,consolas,monospace; Color:rgb (102,102,102)" bounds < code> </code></li></li> <li class="li" style="margin-top:0.583em"><li class="li" style="margin-top:0.583em"><p style="margin-top:0.667em; margin-bottom:0.833em; display:inline">When you set <code style="font-family:Courier,Consolas,monospace; color:rgb(102,102,102)">center</code> the property, the origin value is in the <code style="font-family:Courier,Consolas,monospace; color:rgb(102,102,102)">frame</code> changes Accordingly.</p></li></li> <li class="li" style="margin-top:0.583em"><li class="li" style="margin-top:0.583em"><p style="margin-top:0.667em; margin-bottom:0.833em; display:inline">When you set <code style="font-family:Courier,Consolas,monospace; color:rgb(102,102,102)">bounds</code> the size of the property, the size value in the property <code style="font-family:Courier,Consolas,monospace; color:rgb(102,102,102)">frame</code> changes to match the new size of the Bou NDS Rectangle.</p></li></li> </ul>The runtime interaction model of view allows us to interact with the view in real-time through touch and other Actions. In ios, the interaction model between user action and view is as Follows: 1. The user touches the screen, the event hardware is identified, and is sent to the Uikit Framework. 2, the touch event is packaged into a Uievent class object by the Uikit framework and sent to the corresponding event response View. 3. In the event response view, we can capture the current Uievent event (gesture recognition mechanism or rewrite the Touch series response Function) through the corresponding Function. 4. In view we customize the code to respond, such as: <ul> <li><li>Call <code style="font-size:13px; font-family:Courier,Consolas,monospace; color:rgb(102,102,102)">setNeedsLayout</code> <span style="font-family:‘Lucida Grande‘,‘Lucida Sans Unicode‘,Helvetica,Arial,Verdana,sans-serif; font-size:13px">The method, let the system re-layout (that is, Let the system in the next update process, the active call we rewrite <code style="font-size:13px; font-family:Courier,Consolas,monospace; color:rgb(102,102,102)">layoutSubviews</code> <span style="font-family:‘Lucida Grande‘,‘Lucida Sans Unicode‘,Helvetica,Arial,Verdana,sans-serif; font-size:13px"> </span>)</span></li></li> <li><span style="font-family:‘Lucida Grande‘,‘Lucida Sans Unicode‘,Helvetica,Arial,Verdana,sans-serif; font-size:13px">Call<span style="font-family:‘Lucida Grande‘,‘Lucida Sans Unicode‘,Helvetica,Arial,Verdana,sans-serif; font-size:13px"><span style="font-family:‘Lucida Grande‘,‘Lucida Sans Unicode‘,Helvetica,Arial,Verdana,sans-serif; font-size:13px"> </span></span><code style="font-size:13px; font-family:Courier,Consolas,monospace; color:rgb(102,102,102)"><code style="font-size:13px; font-family:Courier,Consolas,monospace; color:rgb(102,102,102)">setNeedsDisplay</code></code><span style="font-family:‘Lucida Grande‘,‘Lucida Sans Unicode‘,Helvetica,Arial,Verdana,sans-serif; font-size:13px"><span style="font-family:‘Lucida Grande‘,‘Lucida Sans Unicode‘,Helvetica,Arial,Verdana,sans-serif; font-size:13px">or</span></span><code style="font-size:13px; font-family:Courier,Consolas,monospace; color:rgb(102,102,102)"><code style="font-size:13px; font-family:Courier,Consolas,monospace; color:rgb(102,102,102)">setNeedsDisplayInRect:</code></code><span style="font-family:‘Lucida Grande‘,‘Lucida Sans Unicode‘,Helvetica,Arial,Verdana,sans-serif; font-size:13px"><span style="font-family:‘Lucida Grande‘,‘Lucida Sans Unicode‘,Helvetica,Arial,Verdana,sans-serif; font-size:13px">method allows the system to redraw the view Content. (that is, let the system actively invoke our rewritten function during the next round of content updates <code style="font-size:13px; font-family:Courier,Consolas,monospace; color:rgb(102,102,102)">drawRect:</code> <span style="font-family:‘Lucida Grande‘,‘Lucida Sans Unicode‘,Helvetica,Arial,Verdana,sans-serif; font-size:13px"> </span>). </span></span></span></li> <li><li><span style="font-family:‘Lucida Grande‘,‘Lucida Sans Unicode‘,Helvetica,Arial,Verdana,sans-serif; font-size:13px"><span style="font-family:‘Lucida Grande‘,‘Lucida Sans Unicode‘,Helvetica,Arial,Verdana,sans-serif; font-size:13px">Change the properties of the uiview, or notify a controller Object.</span></span></li></li> </ul><span style="font-family:Lucida Grande,Lucida Sans Unicode,Helvetica,Arial,Verdana,sans-serif; font-size:24px"><span style="font-family:Lucida Grande,Lucida Sans Unicode,Helvetica,Arial,Verdana,sans-serif; font-size:24px">tips for using the view</span></span><span style="font-family:Lucida Grande,Lucida Sans Unicode,Helvetica,Arial,Verdana,sans-serif; font-size:12px"><span style="font-family:Lucida Grande,Lucida Sans Unicode,Helvetica,Arial,Verdana,sans-serif; font-size:12px">Apple officials make a number of recommendations on the use of the view, and the more important personal feeling is summarized below:</span></span><span style="font-family:Lucida Grande,Lucida Sans Unicode,Helvetica,Arial,Verdana,sans-serif; font-size:12px"><span style="font-family:Lucida Grande,Lucida Sans Unicode,Helvetica,Arial,Verdana,sans-serif; font-size:12px">1, try to set the view opaque property is Yes. When the opaque property of the view is set to yes, the Uikit framework does not check to see if there is anything that can be rendered after the view (because you have made it clear that the view is opaque), which increases the rendering speed of the Uikit Frame. </span></span><span style="font-family:Lucida Grande,Lucida Sans Unicode,Helvetica,Arial,Verdana,sans-serif; font-size:12px"><span style="font-family:Lucida Grande,Lucida Sans Unicode,Helvetica,Arial,Verdana,sans-serif; font-size:12px">2. Do not add subview to existing UICONTROLR Objects. We should try our best to keep the original ecology for the use of Uicontrol Objects. While it is possible to add your own Subview technology to uicontrol, it is dangerous to do So. Because the implementation details of the Uicontrol object may change when Apple updates the version, the program that we added Subview failed to Run. </span></span><span style="font-family:Lucida Grande,Lucida Sans Unicode,Helvetica,Arial,Verdana,sans-serif; font-size:12px"><span style="font-family:Lucida Grande,Lucida Sans Unicode,Helvetica,Arial,Verdana,sans-serif; font-size:12px"><br></span></span><span style="font-family:Lucida Grande,Lucida Sans Unicode,Helvetica,Arial,Verdana,sans-serif; font-size:12px"><span style="font-family:Lucida Grande,Lucida Sans Unicode,Helvetica,Arial,Verdana,sans-serif; font-size:12px">references:</span></span><span style="font-family:Lucida Grande,Lucida Sans Unicode,Helvetica,Arial,Verdana,sans-serif; font-size:12px"><span style="font-family:Lucida Grande,Lucida Sans Unicode,Helvetica,Arial,Verdana,sans-serif; font-size:12px">Apple Official documentation</span></span><span style="font-family:‘Lucida Grande‘,‘Lucida Sans Unicode‘,Helvetica,Arial,Verdana,sans-serif; font-size:15px; text-align:center; white-space:nowrap"><span style="font-family:‘Lucida Grande‘,‘Lucida Sans Unicode‘,Helvetica,Arial,Verdana,sans-serif; font-size:15px; text-align:center; white-space:nowrap">View programming</span> guide for IOS</span><span style="font-family:‘Lucida Grande‘,‘Lucida Sans Unicode‘,Helvetica,Arial,Verdana,sans-serif; font-size:15px; text-align:center; white-space:nowrap"><span style="font-family:‘Lucida Grande‘,‘Lucida Sans Unicode‘,Helvetica,Arial,Verdana,sans-serif; font-size:15px; text-align:center; white-space:nowrap">https://developer.apple.com/library/prerelease/ios/documentation/WindowsViews/Conceptual/ViewPG_iPhoneOS/ Windowsandviews/windowsandviews.html#//apple_ref/doc/uid/tp40009503-ch2-sw16<br></span></span><span style="font-family:Lucida Grande,Lucida Sans Unicode,Helvetica,Arial,Verdana,sans-serif; font-size:12px"><span style="font-family:Lucida Grande,Lucida Sans Unicode,Helvetica,Arial,Verdana,sans-serif; font-size:12px"><br></span></span><br><br> <p style="font-size:12px;"><p style="font-size:12px;">Copyright Notice: This article for Bo Master original article, without Bo Master permission not Reproduced.</p></p> <p><p>IOS View Programming Guide notes</p></p></span>