iOS --- UIViewController中的loadView使用场景

问题

先看代码， 新建一个UIViewController的子类TestViewController（包含nib文件），imageViewCourse和lbCourse是其两个属性，通过nib的IBOutlet方式添加。

TestViewController *testViewController = [[TestViewController alloc] initWithNibName:@"TestViewController" bundle:nil];

testViewController.imageViewCourse.image = image;
testViewController.lbCourse.text = course;

[self.navigationController presentViewController:testViewController animated:YES completion:nil];

我们使用nib来加载一个TestViewController并对其属性赋值， 然后跳转。问题在于执行完initWithNibName之后，testViewController.imageViewCourse和testViewController.lbCourse都为nil， 则表现出来的是跳转到TestViewController之后， 其中的imageViewCourse和lbCourse中没有内容。

解决方法

使用loadView方法触发nib中UIView的加载。

@property(null_resettable, nonatomic,strong) UIView *view; // The getter first invokes [self loadView] if the view hasn‘t been set yet. Subclasses must call super if they override the setter or getter.
- (void)loadView; // This is where subclasses should create their custom view hierarchy if they aren‘t using a nib. Should never be called directly.
- (void)loadViewIfNeeded NS_AVAILABLE_IOS(9_0); // Loads the view controller‘s view if it has not already been set.

即：

TestViewController *testViewController = [[TestViewController alloc] initWithNibName:@"TestViewController" bundle:nil];
//[testViewController view];
//[testViewController loadView];
[testViewController loadViewIfNeeded];

testViewController.imageViewCourse.image = image;
testViewController.lbCourse.text = course;

[self.navigationController presentViewController:testViewController animated:YES completion:nil];

代码如上， 不做过多解释。三种方式其实殊途同归。