公司的开发的项目要求在状态栏上边加入程序下载的进度条，之前写的程序，由于是根据ipad的朝向来设置自定义的状态栏的frame，以及子视图的frame和transform，出现一些不太容易解决的bug。这两天正好项目不太紧，就好好学习一下这方面的知识，以下是我所总结的一点经验：
这里说明一下，Apple没有开放的状态栏的API，在ios 的官方文档没有提到修改Window Level的方式；
先看一下Window Level的可用的值包括：
1: typedef CGFloat UIWindowLevel;
2: const UIWindowLevel UIWindowLevelNormal; // 0.0
3: const UIWindowLevel UIWindowLevelAlert; // 2000.0
4: const UIWindowLevel UIWindowLevelStatusBar; // 1000.0
默认我们的UIView layer都是在UIWindowLevelNormal上，这也就是为什么系统弹出来的对话框在我们的视图之上，因为它的Window Level级别更高。
根据WindowLevel的原理我们也就知道，如果想在系统的状态栏上，添加自定义的状态栏，就需要比UIWindowLevelStatusBar的级别更高，接下来，用代码说明一下：
首先，先建一个Single View Application，名字自定义就可以了，
然后，新建一个类命名为： StatusBarOverlay 继承自UIWindow类，代码：
StatusBarOverlay.h文件
1: #import
2:
3: @interface StatusBarOverlay : UIWindow{ 4: UIView *contentView;
5: UILabel *textLabel;
6: }
7:
8: @property (nonatomic, retain) UIView *contentView;
9:
10: @property (nonatomic, retain) UILabel *textLabel;
11:
12: @end
StatusBarOverlay.m文件
1: //
2: // StatusBarOverlay.m
3: // StatusBarDemo
4: //
5: // Created by jordy wang on 12-8-7.
6: // Copyright (c) 2012年 __MyCompanyName__. All rights reserved.
7: //
8:
9: #import "StatusBarOverlay.h"
10:
11: #define STATUS_BAR_ORIENTATION [UIApplication sharedApplication].statusBarOrientation
12: #define ROTATION_ANIMATION_DURATION [UIApplication sharedApplication].statusBarOrientationAnimationDuration
13:
14:
15: @interface StatusBarOverlay()
16:
17: - (void)initializeToDefaultState;
18: - (void)rotateStatusBarWithFrame:(NSValue *)frameValue;
19: - (void)setSubViewHFrame;
20: - (void)setSubViewVFrame;
21: @end
22:
23:
24: @implementation StatusBarOverlay
25: @synthesize contentView;
26: @synthesize textLabel;
27:
28: //重写init方法
29: - (id)init
30: { 31: self = [super initWithFrame:CGRectZero];
32: if (self) { 33: self.windowLevel = UIWindowLevelStatusBar + 1;
34: self.frame = [UIApplication sharedApplication].statusBarFrame;
35: [self setBackgroundColor:[UIColor orangeColor]];
36: [self setHidden:NO];
37:
38: //内容视图
39: UIView *_contentView = [[UIView alloc] initWithFrame:self.bounds];
40: self.contentView = _contentView;
41: [self.contentView setAutoresizingMask:UIViewAutoresizingFlexibleWidth];
42: [self.contentView setBackgroundColor:[UIColor cyanColor]];
43: [self addSubview:self.contentView];
44: [_contentView release];
45:
46:
47: //添加textLabel
48: UILabel *_textLabel = [[UILabel alloc] initWithFrame:CGRectMake(30, 0, CGRectGetWidth(self.frame)-60, CGRectGetHeight(self.frame))];
49: self.textLabel = _textLabel;
50: [self.textLabel setBackgroundColor:[UIColor blueColor]];
51: [self.textLabel setFont:[UIFont systemFontOfSize:12]];
52: [self.textLabel setTextAlignment:UITextAlignmentCenter];
53: [self.textLabel setTextColor:[UIColor blackColor]];
54: [self.textLabel setText:@"自定义的状态栏 author by jordy"];
55: [self.contentView addSubview:self.textLabel];
56: [_textLabel release];
57:
58: //注册监听---当屏幕将要转动时，所出发的事件（用于操作本视图改变其frame）
59: [[NSNotificationCenter defaultCenter] addObserver:self selector:@selector(willRotateScreenEvent:) name:UIApplicationWillChangeStatusBarFrameNotification object:nil];
60: //初始化
61: [self initializeToDefaultState];
62: }
63:
64: return self;
65: }
66:
67:
68:
69:
70: //初始化为默认状态
71: - (void)initializeToDefaultState
72: { 73: //获取当前的状态栏位置
74: CGRect statusBarFrame = [UIApplication sharedApplication].statusBarFrame;
75: //设置当前视图的旋转, 根据当前设备的朝向
76: [self rotateStatusBarWithFrame:[NSValue valueWithCGRect:statusBarFrame]];
77:
78:
79:
80: }
81:
82:
83: //旋转屏幕
84: - (void)rotateStatusBarWithFrame:(NSValue *)frameValue
85: { 86: CGRect frame = [frameValue CGRectValue];
87: UIInterfaceOrientation orientation = STATUS_BAR_ORIENTATION;
88:
89: if (orientation == UIDeviceOrientationPortrait) { 90: self.transform = CGAffineTransformIdentity; //屏幕不旋转
91: [self setSubViewVFrame];
92: }else if (orientation == UIDeviceOrientationPortraitUpsideDown) { 93: self.transform = CGAffineTransformMakeRotation(M_PI); //屏幕旋转180度
94: [self setSubViewVFrame];
95: }else if (orientation == UIDeviceOrientationLandscapeRight) { 96: self.transform = CGAffineTransformMakeRotation((M_PI * (-90.0f) / 180.0f)); //屏幕旋转-90度
97: [self setSubViewHFrame];
98: }else if (orientation == UIDeviceOrientationLandscapeLeft){ 99: self.transform = CGAffineTransformMakeRotation(M_PI * 90.0f / 180.0f); //屏幕旋转90度
100: [self setSubViewHFrame];
101: }
102:
103: self.frame = frame;
104: [self.contentView setFrame:self.bounds];
105: }
106:
107: //设置横屏的子视图的frame
108: - (void)setSubViewHFrame
109: { 110: self.textLabel.frame = CGRectMake(30, 0, 1024-60, 20);
111: }
112: //设置竖屏的子视图的frame
113: - (void)setSubViewVFrame
114: { 115: self.textLabel.frame = CGRectMake(30, 0, 748-60, 20);
116: }
117:
118: #pragma mark -
119: #pragma mark 响应屏幕即将旋转时的事件响应
120: - (void)willRotateScreenEvent:(NSNotification *)notification
121: { 122: NSValue *frameValue = [notification.userInfo valueForKey:UIApplicationStatusBarFrameUserInfoKey];
123: [self rotateStatusBarAnimatedWithFrame:frameValue];
124: }
125:
126: - (void)rotateStatusBarAnimatedWithFrame:(NSValue *)frameValue { 127: [UIView animateWithDuration:ROTATION_ANIMATION_DURATION animations:^{ 128: self.alpha = 0;
129: } completion:^(BOOL finished) { 130: [self rotateStatusBarWithFrame:frameValue];
131: [UIView animateWithDuration:ROTATION_ANIMATION_DURATION animations:^{ 132: self.alpha = 1;
133: }];
134: }];
135: }
136:
137: - (void)dealloc
138: { 139: [[NSNotificationCenter defaultCenter] removeObserver:self];
140: [textLabel release];
141: textLabel = nil;
142:
143: [contentView release];
144: contentView = nil;
145:
146: [super dealloc];
147: }
148:
149: @end
由于代码比较简单，并且我在上述代码里有相应的注释，这里需要说明一点的是，默认我们继承自UIWindow的StatusBarOverlay类是hidden状态，需要在初始化的时候设置它的hidden属性为NO，
在屏幕旋转过程中，自定义的状态栏与UIViewController之间的旋转是分离的，所以我们需要做一个隐藏的动画，在旋转过程前先隐藏自定义的状态栏，旋转结果后设置显示状态。
如果需要做一种动画，比方从底部下移显示一条信息，隔N秒后又自动收回的动画，直接设置自定义的视图的y坐标就可以了，默认y坐标设置是0。
最后， 使用它的方式也比较简单，只需要初始化，代码：
StatusBarOverlay *statusBarOverlay = [[StatusBarOverlay alloc] init];
由于我公司的需求是开机自动下载的功能，所以我在初始化的时候，是放在了AppDelegate中。