在iOS開發過程中，視圖的層次是非常重要的，往往一不小心就會造成出乎意料的bug。通常體現在button不靈敏或拖拽失效等；
Xcode6出來后，有個功能叫View UI Hierarchy，即UI檢視器。它的位置在xcode中的
它非常的方便我們觀察UI的位置及視圖的層次。
在iOS中管理視圖層次的二個重要方法就是
//將view顯示在最前
- (void)bringSubviewToFront:(UIView *)view;
例如：[self.view bringSubviewToFront:self.firstView];
//將view顯示在最后
- (void)sendSubviewToBack:(UIView *)view;
例如：[self.view sendSubviewToBack:self.firstView];
在這里我將着重講下sendSubviewToBack一個很妙的用法。
常常在處理文本框輸入內容時，通常是注冊一個通知，然后將view向上頂,
就像這樣
//注冊鍵盤通知
[[NSNotificationCenter defaultCenter] addObserver:self
selector:@selector(keyboardWillShow:)
name:UIKeyboardWillShowNotification
object:nil];
[[NSNotificationCenter defaultCenter] addObserver:self
selector:@selector(keyboardWillHide:)
name:UIKeyboardWillHideNotification
object:nil];
然后再將界面向上頂
-(void) keyboardWillShow:(NSNotification *)note{
// get keyboard size and loctaion
CGRect keyboardBounds;
[[note.userInfo valueForKey:UIKeyboardFrameEndUserInfoKey] getValue: &keyboardBounds];
NSNumber *duration = [note.userInfo objectForKey:UIKeyboardAnimationDurationUserInfoKey];
NSNumber *curve = [note.userInfo objectForKey:UIKeyboardAnimationCurveUserInfoKey];
// Need to translate the bounds to account for rotation.
keyboardBounds = [self.view convertRect:keyboardBounds toView:nil];
// get a rect for the textView frame
if ([self.contextView isFirstResponder]) {
CGRect containerFrame = self.creatView.frame;
containerFrame.origin.y = self.view.bounds.size.height - (keyboardBounds.size.height + containerFrame.size.height);
containerFrame.origin.x = 21;
containerFrame.size.width=278;
// animations settings
[UIView beginAnimations:nil context:NULL];
[UIView setAnimationBeginsFromCurrentState:YES];
[UIView setAnimationDuration:[duration doubleValue]];
[UIView setAnimationCurve:[curve intValue]];
// set views with new info
self.creatView.frame = containerFrame;
// commit animations
[UIView commitAnimations];
}
}
但這樣做的話會有個不好的地方，那就是可能會將自定義的導航欄頂出界面外了，就像這樣
這樣的話雖說鍵盤並沒有擋住文本框的效果實現了，但界面體驗不太好。那么該怎么辦呢。
其實我們分析原因可知，之所以導航欄向上頂了，因為其所屬的層在整個view中
- (BOOL)textViewShouldBeginEditing:(UITextView *)textView{
if ([textView isKindOfClass:[self.secondview.descriptionTextView class]]) {
[self.view sendSubviewToBack:self.secondview];
[UIView animateWithDuration:0.35f animations:^{
[self.secondview setFrame:CGRectMake(self.secondview.frame.origin.x, self.secondview.frame.origin.y - 216.0f, self.secondview.frame.size.width, self.secondview.frame.size.height)];
} completion:^(BOOL finished) {
}];
}
return YES;
}
調整后，可以看到，鍵盤彈出后，導航欄並沒有消失
至此，問題完美解決！