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81 lines
2.7 KiB
Markdown
81 lines
2.7 KiB
Markdown
# loadView
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1. Purpose: load the controller's view
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2. When it's called: it's called the first time the controller's view is used
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3. Use case: implement this method when you want to provide a custom view for the controller
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Accessing the controller's view is equivalent to calling the controller's view getter:
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```objective-c
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-(UIView *)view
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{
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if(_view == nil){
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[self loadView];
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[self viewDidLoad];
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}
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return _view;
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}
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```
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# Controller view loading flow
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- The controller's `init` method internally calls `initWithNibName`
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`MyViewController *vc = [[MyViewController alloc] init];`
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Notes:
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The system's decision logic assumes: no nibName specified; no custom loadView method; the controller is named ...Controller
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Decision rules:
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- Check whether a nibName was specified; if specified, load that nib
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- Check whether there's an xib with the same name as the controller but without "Controller" in its name; if present, load it
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- If the previous step doesn't find one, check whether an xib with the same name as the controller class exists; if present, load it
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- If no xib describes the controller's view, do not load any xib
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## How MyViewController loads its view
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- Check whether an xibName was specified; if so, load the specified xib
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- Check whether there's an xib with the same name as the controller class but without "Controller" in the name
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- Check whether there's an xib with the same name as the controller class; if present, load it
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- Otherwise, create an empty view directly
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Example
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```objective-c
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// in AppDelegate
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ViewController *vc = [[ViewController alloc] init];
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vc.view.backgroundColkor = [UIColor redColor];
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self.window.rootViewController = vc;
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[pself.window makeKeyAndVisable];
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// ViewController
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-(UIView *)view{
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if(!_view){
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[self loadView];
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[self viewDidLoad];
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}
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}
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-(void)loadView{
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UIView*view = [[UIView alloc] initWithFrame:[UIScreen mainScreen].bounds];
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view.backgroundColor = [UIColor greenColor];
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self.view = view;
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}
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-(void)viewDidload{
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[super viewDidload];
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self.view.backgroundColor = [UIColor brownColor];
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}
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```
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### What color will the interface be at this point?
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Many people might answer "green." Actually, the answer is red.
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Why? In AppDelegate, `vc.view.backgroundColor` calls vc's view getter. Inside the getter it checks if `_view` exists; if not, it creates a new UIView by calling `[self loadView]`. After creating the view it calls `viewDidLoad`; if the view already exists it returns it directly. So the sequence is: first green, then brown, and finally red.
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#### An official explanation
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