简单的仿Path风格菜单的实现

刚开始只是在顶部导航栏添加两个按钮，用来控制主屏的左右移动。

- (void)setupNavBar
{
    _navBar = [[UIView alloc] initWithFrame:CGRectMake(0, 0, self.middleView.frame.size.width, 44)];
    self.navBar.backgroundColor = [UIColor blueColor];
    [self.middleView addSubview:self.navBar];
    
    UIButton *leftNavBtn = [UIButton buttonWithType:UIButtonTypeRoundedRect];
    leftNavBtn.frame = CGRectMake(10, 0, 44, 44);
    [self.navBar addSubview:leftNavBtn];
    [leftNavBtn setTitle:@"Left" forState:UIControlStateNormal];
    [leftNavBtn addTarget:self action:@selector(leftNavBtnDidClick:) forControlEvents:UIControlEventTouchUpInside];
    
    UIButton *rightNavBtn = [UIButton buttonWithType:UIButtonTypeRoundedRect];
    rightNavBtn.frame = CGRectMake(self.navBar.frame.size.width - 10 - 44, 0, 44, 44);
    [self.navBar addSubview:rightNavBtn];
    [rightNavBtn setTitle:@"Right" forState:UIControlStateNormal];
    [rightNavBtn addTarget:self action:@selector(rightNavBtnDidClick:) forControlEvents:UIControlEventTouchUpInside];
}

并且是通过点击按钮修改button的tag来记录当前屏幕展示的状态，有点挫。

后来整理了下，设置一个状态变量：

typedef enum _screenStateType {
    kNormalState = 0,
    kLeftState,     // Show the left-view
    kRightState,    // Show the right-view
    kDriftingState  // Drifting
} ScreenStateType;

通过屏幕状态变量来控制屏幕的左右滑动：

#pragma mark - Slide to Left or Right

#define LEFT_SLIDE_OFFSET   260.0f
#define RIGHT_SLIDE_OFFSET  (-260.0f)

- (void)leftNavBtnDidClick:(UIButton *)btn
{
    if (kNormalState == self.screenState) {
        [self slideFromeState:self.screenState toState:kLeftState];
    } else {
        [self slideFromeState:self.screenState toState:kNormalState];
    }
}

- (void)rightNavBtnDidClick:(UIButton *)btn
{
    if (kNormalState == self.screenState) {
        [self slideFromeState:self.screenState toState:kRightState];
    } else {
        [self slideFromeState:self.screenState toState:kNormalState];
    }
}

- (void)slideFromeState:(ScreenStateType)oState toState:(ScreenStateType)dState
{
    if (self.isSliding) return ;
    self.isSliding = YES;
    
    __block CGRect rect = self.middleView.frame;
    rect.origin.x = 0.0f;
    
    id completionBlk = nil;
    
    switch (oState) {
        case kNormalState:
            if (kLeftState == dState) {
                self.rightView.hidden = YES;
                rect.origin.x = LEFT_SLIDE_OFFSET;
            } else if (kRightState == dState) {
                self.leftView.hidden = YES;
                rect.origin.x = RIGHT_SLIDE_OFFSET;
            }
            break;
            
        case kLeftState:
        case kRightState:
            if (kNormalState == dState) {
                completionBlk = ^(BOOL finished) { self.leftView.hidden = NO; self.rightView.hidden = NO; };
            }
            break;
            
        case kDriftingState:
            if (kLeftState == dState) {
                rect.origin.x = LEFT_SLIDE_OFFSET;
            } else if (kRightState == dState) {
                rect.origin.x = RIGHT_SLIDE_OFFSET;
            } else if (kNormalState == dState) {
                completionBlk = ^(BOOL finished) { self.leftView.hidden = NO; self.rightView.hidden = NO; };
            }
            break;
            
        default:
            break;
    }
    
    id animationBlk = ^{ self.middleView.frame = rect; };
    [UIView animateWithDuration:0.3f animations:animationBlk completion:completionBlk];
    
    self.screenState = dState;
    self.isSliding = NO;
}

当完成这样的功能后，我在模拟器上跑了下，觉得还行。不过在真机跑的时候，我习惯用拇指来滑动，而不是用导航栏的按钮。

当修改为可以通过手指滑屏后，又发现太容易滑了，有点影响用户体验，所以在移动过程先尝试检测下用户是否真的想滑屏：

#pragma mark - Finger Touch

- (void)touchesBegan:(NSSet *)touches withEvent:(UIEvent *)event
{
    UITouch *touch = [touches anyObject];
    CGPoint fingerPoint = [touch locationInView:self.middleView];
    if ([self.middleView pointInside:fingerPoint withEvent:nil]) {
        fingerPoint = [touch locationInView:self.view];
        self.lastFingerX = fingerPoint.x;
    }
}

- (void)touchesMoved:(NSSet *)touches withEvent:(UIEvent *)event
{
    UITouch *touch = [touches anyObject];
    CGPoint fingerPoint = [touch locationInView:self.view];
    
    // The user really wants to move the screen ?
    if (!self.canDrag && abs(fingerPoint.x - self.lastFingerX) > 30) {
        self.canDrag = YES ;
        self.lastFingerX = fingerPoint.x;
    }
    
    if (!self.canDrag) return ;
    
    CGRect rect = self.middleView.frame;
    rect.origin.x += (fingerPoint.x - self.lastFingerX);
    rect.origin.x = (rect.origin.x > LEFT_SLIDE_OFFSET) ? LEFT_SLIDE_OFFSET : rect.origin.x;
    rect.origin.x = (rect.origin.x < RIGHT_SLIDE_OFFSET) ? RIGHT_SLIDE_OFFSET : rect.origin.x;
    self.middleView.frame = rect;
    
    if (rect.origin.x > 0) {
        self.rightView.hidden = YES;
        self.leftView.hidden = NO;
    } else if (rect.origin.x < 0) {
        self.leftView.hidden = YES;
        self.rightView.hidden = NO;
    } else {
        self.leftView.hidden = self.rightView.hidden = NO;
    }
    
    self.lastFingerX = fingerPoint.x;
}

- (void)touchesEnded:(NSSet *)touches withEvent:(UIEvent *)event
{
    self.canDrag = NO;
    
    CGFloat boundary = 50.0f;
    CGRect rect = self.middleView.frame;
    
    ScreenStateType lastScreenState = self.screenState;
    self.screenState = kDriftingState;
    
    switch (lastScreenState) {
        case kNormalState:
            if (rect.origin.x < (0 - boundary)) {
                [self slideFromeState:self.screenState toState:kRightState];
            } else if (rect.origin.x > (0 + boundary)) {
                [self slideFromeState:self.screenState toState:kLeftState];
            } else {
                [self slideFromeState:self.screenState toState:kNormalState];
            }
            break;
            
        case kLeftState:
            if (rect.origin.x < LEFT_SLIDE_OFFSET - boundary) {
                [self slideFromeState:self.screenState toState:kNormalState];
            } else {
                [self slideFromeState:self.screenState toState:kLeftState];
            }
            break;
            
        case kRightState:
            if (rect.origin.x > RIGHT_SLIDE_OFFSET + boundary) {
                [self slideFromeState:self.screenState toState:kNormalState];
            } else {
                [self slideFromeState:self.screenState toState:kRightState];
            }
            break;
            
        default:
            [self slideFromeState:self.screenState toState:kNormalState];
            break;
    }
}

完整的代码参见：https://gist.github.com/3857426