' - '的右操作数是垃圾值

Question

我第一次使用静态分析仪,很难弄清楚箭头.在看了一些关于SO的类似问题后,我认为问题是CGSize大小是零值,但我不完全确定它是如何工作的.

这是代码:

 - (void)keyboardDidShow:(NSNotification*)notification {
    CGSize size = CGSizeMake(0, 0);
    size = [self keyboardSize:notification];
      if (UIInterfaceOrientationIsLandscape(self.interfaceOrientation)) {
            detailTableView.frame = CGRectMake(detailTableView.frame.origin.x, detailTableView.frame.origin.y,
                                       detailTableView.frame.size.width, kTableViewMovableHeight + kTableViewDefaultHeight -  size.height
                                       );
    //detailTableView.scrollEnabled = YES;
    }
}


- (CGSize)keyboardSize:(NSNotification *)aNotification {
NSDictionary *info = [aNotification userInfo];
NSValue *beginValue = [info objectForKey:UIKeyboardFrameEndUserInfoKey];
UIDeviceOrientation orientation = [[UIDevice currentDevice] orientation];
CGSize keyboardSize;
UIDeviceOrientation _screenOrientation = orientation;
if ([UIKeyboardDidShowNotification isEqualToString:[aNotification name]]) {
    if (UIDeviceOrientationIsPortrait(orientation)) {
        keyboardSize = [beginValue CGRectValue].size;
    } else {
        keyboardSize.height = [beginValue CGRectValue].size.width;
        keyboardSize.width = [beginValue CGRectValue].size.height;
    }
} else if ([UIKeyboardWillHideNotification isEqualToString:[aNotification name]]) {
    if (_screenOrientation == orientation) {
        if (UIDeviceOrientationIsPortrait(orientation)) {
            keyboardSize = [beginValue CGRectValue].size;
        } else {
            keyboardSize.height = [beginValue CGRectValue].size.width;
            keyboardSize.width = [beginValue CGRectValue].size.height;
        }
        // rotated
    } else if (UIDeviceOrientationIsPortrait(orientation)) {
        keyboardSize.height = [beginValue CGRectValue].size.width;
        keyboardSize.width = [beginValue CGRectValue].size.height;
    } else {
        keyboardSize = [beginValue CGRectValue].size;
    }
}
return keyboardSize;
}

Answer 1

1. CGSize是一个C结构
2. [self keyboardSize:notification] 可能会返回零

声明C结构时,其值具有垃圾值.也就是说,之前的那段记忆中的任何东西.如果你的调用keyboardSize返回一个未初始化的CGSize,那个C结构将具有所谓的"垃圾值".

现在我看到了CGSize的实现,将keyboardSize方法中变量keyboardSize的声明更改为:

CGSize keyboardSize = CGSizeMake(0, 0);