iOS实现全局悬浮按钮

@interface AppDelegate : UIResponder <UIApplicationDelegate>

@property (strong, nonatomic) UIWindow *window;
@property (strong, nonatomic) UIButton *button;

@end

- (UIButton*)button {
    if (!_button) {
        _button = [UIButton buttonWithType:UIButtonTypeCustom];
        _button.frame = CGRectMake(258, 450, 60, 60);//初始在屏幕上的位置
        [_button setImage:[UIImage imageNamed:@"bcl_btn_whole"] forState:UIControlStateNormal];
    }
    return _button;
}

-(void)createButton{
    if (!_button) {
        _window = [[UIApplication sharedApplication] keyWindow];
        _window.backgroundColor = [UIColor whiteColor];
        [_window addSubview:self.button];
        UIPanGestureRecognizer *pan = [[UIPanGestureRecognizer alloc]initWithTarget:
                                       self action:@selector(locationChange:)];
        pan.delaysTouchesBegan = YES;
        [_button addGestureRecognizer:pan];
    }
}

- (BOOL)application:(UIApplication *)application didFinishLaunchingWithOptions:(NSDictionary *)launchOptions {
    [self performSelector:@selector(createButton) withObject:nil afterDelay:2];
}

-(void)locationChange:(UIPanGestureRecognizer*)p{
    CGFloat HEIGHT=_button.frame.size.height;
    CGFloat WIDTH=_button.frame.size.width;
    BOOL isOver = NO;
    CGPoint panPoint = [p locationInView:[UIApplication sharedApplication].windows[0]];
    CGRect frame = CGRectMake(panPoint.x, panPoint.y, HEIGHT, WIDTH);
    NSLog(@"%f--panPoint.x-%f-panPoint.y-", panPoint.x, panPoint.y);
    if(p.state == UIGestureRecognizerStateChanged){
        _button.center = CGPointMake(panPoint.x, panPoint.y);
    }
    else if(p.state == UIGestureRecognizerStateEnded){
        if (panPoint.x + WIDTH > KScreenWidth) {
            frame.origin.x = KScreenWidth - WIDTH;
            isOver = YES;
        } else if (panPoint.y + HEIGHT > KScreenHeight) {
            frame.origin.y = KScreenHeight - HEIGHT;
            isOver = YES;
        } else if(panPoint.x - WIDTH / 2< 0) {
            frame.origin.x = 0;
            isOver = YES;
        } else if(panPoint.y - HEIGHT / 2 < 0) {
            frame.origin.y = 0;
            isOver = YES;
        }
        if (isOver) {
            [UIView animateWithDuration:0.3 animations:^{
                self.button.frame = frame;
            }];
        }