实例022 设置视图位置互换显示（1）

实例说明

在iOS应用中，可以使用sendSubviewToFront方法将某个视图放在前方显示，使用sendSubview-ToBack方法将某个视图放在后方显示。

本实例的功能是，设置两个重叠的视图，可以设置其中的一个视图靠前显示还是靠后隐藏显示。本实例首先设置了两个标签代表两块视图区域，然后在下方设置了“bringFront”按钮和“sendBack”按钮。单击这两个按钮后，会实现指定标签块的前置和靠后显示效果。

具体实现

实例文件UIkitPrjSiblings.h的实现代码如下所示。

#import "SampleBaseController.h"
@interface UIKitPrjSiblings : SampleBaseController
{
 @private
  UILabel* labelA_;
  UILabel* labelB_;
}
@end

实例文件UIkitPrjSiblings.m的实现代码如下所示。

#import "UIKitPrjSiblings.h"
#pragma mark ----- Private Methods Definition -----
@interface UIKitPrjSiblings ()
- (void)bringFrontDidPush;
- (void)sendBackDidPush;
@end
#pragma mark ----- Start Implementation For Methods -----
@implementation UIKitPrjSiblings
// finalize
- (void)dealloc {
  [labelA_ release];
  [labelB_ release];
  [super dealloc];
}
- (void)viewDidLoad {
  [super viewDidLoad];
  self.view.backgroundColor = [UIColor whiteColor];
  // 追加标签A
  labelA_ = [[UILabel alloc] initWithFrame:CGRectMake( 10, 10, 150, 150 )];
  labelA_.backgroundColor = [UIColor redColor];
  labelA_.textAlignment = UITextAlignmentCenter;
  labelA_.text = @"A";
  [self.view addSubview:labelA_];
  // 追加标签B
  labelB_ = [[UILabel alloc] initWithFrame:CGRectMake( 100, 100, 150, 150 )];
  labelB_.backgroundColor = [UIColor blueColor];
  labelB_.textAlignment = UITextAlignmentCenter;
  labelB_.text = @"B";
  [self.view addSubview:labelB_];
  // 追加bringFront按钮
  UIButton* bringFrontButton = [UIButton buttonWithType:UIButtonTypeRoundedRect];
  bringFrontButton.frame = CGRectMake( 0, 0, 100, 40 );
  CGPoint newPoint = self.view.center;
  newPoint.x -= 50;
  newPoint.y = self.view.frame.size.height -100;
  bringFrontButton.center = newPoint;
  [bringFrontButton setTitle:@"bringFront" forState:UIControlStateNormal];
  [bringFrontButton addTarget:self
                    action:@selector(bringFrontDidPush)
          forControlEvents:UIControlEventTouchUpInside]
  // 追加sendBack按钮
  UIButton* sendBackButton = [UIButton buttonWithType:UIButtonTypeRoundedRect];
  sendBackButton.frame = CGRectMake( 0, 0, 100, 40 );
  newPoint.x += 100;
  sendBackButton.center = newPoint;
  [sendBackButton setTitle:@"sendBack" forState:UIControlStateNormal];
  [sendBackButton addTarget:self
                  action:@selector(sendBackDidPush)
          forControlEvents:UIControlEventTouchUpInside];
  [self.view addSubview:bringFrontButton];
  [self.view addSubview:sendBackButton];
}
#pragma mark ----- Private Methods -----
- (void)bringFrontDidPush {
  [self.view bringSubviewToFront:labelA_];
}
- (void)sendBackDidPush {
  [self.view sendSubviewToBack:labelA_];
}
- (void)touchesEnded:(NSSet*)touches withEvent:(UIEvent*)event {
  [self.navigationController setNavigationBarHidden:NO animated:YES];
}
@end

执行后的效果如图2-26所示。

图2-26 执行效果