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Chapter1 - iOS/1.3.md

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+# loadView
+
+1. Purpose: load the controller's view
+2. When it's called: it's called the first time the controller's view is used
+3. Use case: implement this method when you want to provide a custom view for the controller
+
+Accessing the controller's view is equivalent to calling the controller's view getter:
+```objective-c
+-(UIView *)view
+{
+    if(_view == nil){
+        [self loadView];
+        [self viewDidLoad];
+    }
+    return _view;
+}
+```
+
+# Controller view loading flow
+![Controller view loading flow](../assets/2287777-b6128646373dfffb.png)
+
+- The controller's `init` method internally calls `initWithNibName`
+
+  `MyViewController *vc = [[MyViewController alloc] init];`
+
+Notes:
+
+The system's decision logic assumes: no nibName specified; no custom loadView method; the controller is named ...Controller
+
+Decision rules:
+
+- Check whether a nibName was specified; if specified, load that nib
+- Check whether there's an xib with the same name as the controller but without "Controller" in its name; if present, load it
+- 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
+- If no xib describes the controller's view, do not load any xib
+
+## How MyViewController loads its view
+
+- Check whether an xibName was specified; if so, load the specified xib
+- Check whether there's an xib with the same name as the controller class but without "Controller" in the name
+- Check whether there's an xib with the same name as the controller class; if present, load it
+- Otherwise, create an empty view directly
+
+Example
+
+```objective-c
+// in AppDelegate
+ViewController *vc = [[ViewController alloc] init];
+vc.view.backgroundColkor = [UIColor redColor];
+self.window.rootViewController = vc;
+[pself.window makeKeyAndVisable];
+
+// ViewController
+-(UIView *)view{
+    if(!_view){
+        [self loadView];
+        [self viewDidLoad];
+    }
+}
+
+-(void)loadView{
+    UIView*view = [[UIView alloc] initWithFrame:[UIScreen mainScreen].bounds];
+    view.backgroundColor = [UIColor greenColor];
+    self.view = view;
+}
+
+-(void)viewDidload{
+    [super viewDidload];
+    self.view.backgroundColor = [UIColor brownColor];
+}
+```
+
+### What color will the interface be at this point?
+
+Many people might answer "green." Actually, the answer is red.
+
+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.
+
+#### An official explanation
+
+![Apple documentation](../assets/2287777-8ff7c3b976ffb29a.png)