UINavigationBar和UITabBar 上滚渐变显示 下拉渐变隐藏

   <p>由于项目需求要做一个这样的功能，所以做好之后，抽取出来，封装了下，希望能帮到有需要的朋友。</p>    <h2>1.效果图</h2>    <p style="text-align:center"><img src="https://simg.open-open.com/show/e19585915d148c54507240545ec5022f.gif"></p>    <p style="text-align:center">UINavigationBar和UITabbar渐变.gif</p>    <h2>2.思路</h2>    <h2>A. 设置tableView</h2>    <p>a.因为当UINavigationBar和UITabBar隐藏的时候，tableView要完全占据整个屏幕，当UINavigationBar和UITabBar显示的时候，tableView又要显示在UINavigationBar下方，所以需要设置tablewView的frame和contentInset：</p>    <pre>  <code class="language-objectivec">self.tableView.frame = CGRectMake(0, -kNavigationBarHeight,kScreenWidth,kScreenHeight+kNavigationBarHeight);     self.tableView.contentInset = UIEdgeInsetsMake(kNavigationBarHeight,0,0,0);</code></pre>    <p>B.当tableView向上移动一个属性,UINavigationBar要向上移动一个属性，UITabBar要向下移动一个像素，所以需要在- (void)scrollViewDidScroll:(UIScrollView*)scrollView方法中获取每一次tableView滚动的距离，因此需要记住上次tableView的偏移量距离：CGFloat_originalOffsetY;//上一次偏移量</p>    <pre>  <code class="language-objectivec">CGFloat offsetY = scrollView.contentOffset.y-_originalOffsetY;//获取每次滚动偏移的距离    _originalOffsetY = scrollView.contentOffset.y;//将这次tableView偏移量重新赋值给_originalOffsetY</code></pre>    <p>又因为当UINavigationBar和UITabBar已经隐藏，继续向上滚动，已经不需要隐藏，同样的当tableView滚动到最后滚不动的时候UINavigationBar和UITabBar也不需要移动，所以添加判断条件</p>    <pre>  <code class="language-objectivec">//判断是否滚动到底部  CGFloat bottomOffset = scrollView.contentSize.height- scrollView.contentOffset.y- scrollView.frame.size.height;     //判断UINavigationBar是否已经隐藏  scrollView.contentOffset.y > - (2*kNavigationBarHeight)    //UIScrollView 函数  - (void)scrollViewDidScroll:(UIScrollView*)scrollView {        CGFloat bottomOffset = scrollView.contentSize.height- scrollView.contentOffset.y- scrollView.frame.size.height;         if(scrollView.contentOffset.y> - kNavigationBarHeight && bottomOffset >0) {              CGFloat offsetY = scrollView.contentOffset.y-_originalOffsetY;              [self moveNavigationBarAndStatusBarByOffsetY:offsetY];          }       _originalOffsetY= scrollView.contentOffset.y;   }</code></pre>    <p>C.moveNavigationBarAndStatusBarByOffsetY函数设置UINavigationBar和UITabBar相关transform.ty位置的值，同时设置相关背景图片的透明度</p>    <pre>  <code class="language-objectivec">// 通过偏移量移动NavigationBar和StatusBar  - (void)moveNavigationBarAndStatusBarByOffsetY:(CGFloat)offsetY {        CGFloat transformTy = self.navigationController.navigationBar.transform.ty;      CGFloat tabbarTransformTy = self.tabBarController.tabBar.transform.ty;  // 向上滚动      if (offsetY > 0) {          if (fabs(transformTy) >= kNavigationBarHeight) {          //当NavigationBar的transfrom.ty大于NavigationBar高度，导航栏离开可视范围，设置NavigationBar隐藏              [self setNavigationBarTransformProgress:1 navigationBarStatusType:NavigationBarStatusOfTypeHidden];      } else {          //当NavigationBar的transfrom.ty小于NavigationBar高度，导航栏在可视范围内，设置NavigationBar偏移位置和背景透明度                  [self setNavigationBarTransformProgress:offsetY navigationBarStatusType:NavigationBarStatusOfTypeNormal];          }            if (fabs(tabbarTransformTy) >= kStatusBarHeight) {              //当StatusTabBar的transfrom.ty大于StatusTabBar高度，导航栏离开可视范围，设置StatusTabBar隐藏             [self setStatusBarTransformProgress:1 statusBarStatusType:StatusBarStatusTypeOfHidden];          } else {              //当当StatusTabBar的transfrom.ty小于StatusTabBar高度，导航栏在可视范围内，设置StatusTabBar偏移位置和背景透明度              [self setStatusBarTransformProgress:offsetY statusBarStatusType:StatusBarStatusTypeOfNormal];          }          // 向下滚动          } else if(offsetY < 0){          if (transformTy < 0 && fabs(transformTy) <= kNavigationBarHeight) {              //当NavigationBar的transfrom.ty小于NavigationBar高度，导航栏进入可视范围内，设置NavigationBar偏移位置和背景透明度              [self setNavigationBarTransformProgress:offsetY navigationBarStatusType:NavigationBarStatusOfTypeNormal];      } else {          //当NavigationBar的transfrom.ty超过NavigationBar原来位置，设置NavigationBar显示          [self setNavigationBarTransformProgress:0 navigationBarStatusType:NavigationBarStatusOfTypeShow];          }            if (tabbarTransformTy <= kStatusBarHeight && tabbarTransformTy > 0) {              //当StatusTabBar的transfrom.ty小于StatusTabBar高度，导航栏进入可视范围内，设置StatusTabBar偏移位置和背景透明度              [self setStatusBarTransformProgress:offsetY statusBarStatusType:StatusBarStatusTypeOfNormal];          } else {              //当StatusTabBar的transfrom.ty超过StatusTabBar原来位置，设置StatusTabBar显示              [self setStatusBarTransformProgress:0 statusBarStatusType:StatusBarStatusTypeOfShow];          }      }  }</code></pre>    <p>D.通过这两个函数</p>    <pre>  <code class="language-objectivec">- (void)setStatusBarTransformProgress:(CGFloat)progress statusBarStatusType:(StatusBarStatusType)statusBarStatusType</code></pre>    <p>和</p>    <pre>  <code class="language-objectivec">- (void)setNavigationBarTransformProgress:(CGFloat)progress navigationBarStatusType:(NavigationBarStatusType)navigationBarStatusType</code></pre>    <p>改变NavigationBarStatusTabBar背景图透明图和颜色</p>    <pre>  <code class="language-objectivec">// 根据传入的类型和渐变程度,改变StatusBar的颜色和位置  - (void)setStatusBarTransformProgress:(CGFloat)progress statusBarStatusType:    (StatusBarStatusType)statusBarStatusType{    CGFloat transfromTy = self.tabBarController.tabBar.transform.ty;      if (statusBarStatusType == StatusBarStatusTypeOfHidden) {          if (transfromTy != kStatusBarHeight) {              [self.tabBarController.tabBar fj_moveByTranslationY:kStatusBarHeight * progress];              [self.tabBarController.tabBar fj_setImageViewAlpha:progress];          }       }else if(statusBarStatusType == StatusBarStatusTypeOfNormal) {          [self.tabBarController.tabBar fj_setTranslationY:-progress];           CGFloat alpha = 1 - fabs(self.tabBarController.tabBar.transform.ty)/kStatusBarHeight;          [self.tabBarController.tabBar fj_setImageViewAlpha:alpha];      }else if(statusBarStatusType == StatusBarStatusTypeOfShow) {          if (transfromTy != 0) {             [self.tabBarController.tabBar fj_moveByTranslationY: -kStatusBarHeight * progress];              [self.tabBarController.tabBar fj_setImageViewAlpha:(1-progress)];          }      }  }</code></pre>    <p>// 根据传入的类型和渐变程度,改变NavigationBar的颜色和位置</p>    <pre>  <code class="language-objectivec">- (void)setNavigationBarTransformProgress:(CGFloat)progress navigationBarStatusType:(NavigationBarStatusType)navigationBarStatusType{  CGFloat transfromTy = self.navigationController.navigationBar.transform.ty;  if (navigationBarStatusType == NavigationBarStatusOfTypeHidden) {      if(transfromTy != -kNavigationBarHeight){          [self.navigationController.navigationBar fj_moveByTranslationY:-kNavigationBarHeight * progress];          [self.navigationController.navigationBar fj_setImageViewAlpha:progress];      }  }else if(navigationBarStatusType == NavigationBarStatusOfTypeNormal) {      [self.navigationController.navigationBar fj_setTranslationY: - progress];      CGFloat alpha = 1 - fabs(self.navigationController.navigationBar.transform.ty)/kNavigationBarHeight;      [self.navigationController.navigationBar fj_setImageViewAlpha:alpha];  }else if(navigationBarStatusType == NavigationBarStatusOfTypeShow) {      if(transfromTy != 0){          [self.navigationController.navigationBar fj_moveByTranslationY:-kNavigationBarHeight * progress];          [self.navigationController.navigationBar fj_setImageViewAlpha:(1-progress)];      }  }</code></pre>    <p>}</p>    <p>E.设置UITabBar和UINavigationBar类方法</p>    <p>// 设置背景图透明度</p>    <pre>  <code class="language-objectivec">- (void)fj_setImageViewAlpha:(CGFloat)alpha;  // 根据translationY在原来位置上偏移  - (void)fj_setTranslationY:(CGFloat)translationY;  // 设置偏移translationY  - (void)fj_moveByTranslationY:(CGFloat)translationY;</code></pre>    <p>F.在- (void)scrollViewDidEndDragging:(UIScrollView *)scrollView willDecelerate:(BOOL)decelerate函数里面判断当前NavigationBar偏移是否超过一半，如果一半则动画隐藏，如果没有则动画显示:</p>    <pre>  <code class="language-objectivec">//恢复或隐藏navigationBar和statusBar  - (void)restoreNavigationBarAndStatusBarWithContentOffset:(CGPoint)contentOffset {      CGFloat navigationBarCenterHeight  = kNavigationBarHeight/2.0;      CGFloat transformTy = self.navigationController.navigationBar.transform.ty;      if (transformTy < 0 && transformTy > -kNavigationBarHeight) {          if (transformTy < -navigationBarCenterHeight && contentOffset.y > -navigationBarCenterHeight) {              [UIView animateWithDuration:kDefaultAnimationTime animations:^{                  [self hideNavigationBarAndStatusBar];              }];            }else {              [UIView animateWithDuration:kDefaultAnimationTime animations:^{                  [self showNavigationBarAndStatusBar];              }];          }      }  }</code></pre>    <h2> </h2>    <p> </p>    <p> </p>