调整导航条上leftBarButtonItem和rightBarButtonItem与屏幕边界的间距

我们发现，在设置navigationItem的leftBarButtonItem或rightBarButtonItem时，用CustomView初始化UIBarButtonItem，不论怎么设置CustomView的frame，添加到导航条上之后总是和屏幕边界有一定的间距（5pix），如何自由调整这个间距呢？

初始化一个用于控制间距的UIBarButtonItem实例negativeSpacer，并设置negativeSpacer的width属性的值，设为-5的时候，正好可以使按钮与屏幕边界值为0，以rightBarButtonItem情况为例

[plain] view plaincopy

1. UIButton *btn = [UIButton buttonWithType:UIButtonTypeRoundedRect];
2. /**
3. *  设置frame只能控制按钮的大小
4. */
5. btn.frame= CGRectMake(0, 0, 40, 44);
6. [btn addTarget:self action:@selector(buttonClicked) forControlEvents:UIControlEventTouchUpInside];
7. UIBarButtonItem *btn_right = [[UIBarButtonItem alloc] initWithCustomView:btn];
8. UIBarButtonItem *negativeSpacer = [[UIBarButtonItem alloc]
9. initWithBarButtonSystemItem:UIBarButtonSystemItemFixedSpace
10. target:nil action:nil];
11. /**
12. *  width为负数时，相当于btn向右移动width数值个像素，由于按钮本身和边界间距为5pix，所以width设为-5时，间距正好调整
13. *  为0；width为正数时，正好相反，相当于往左移动width数值个像素
14. */
15. negativeSpacer.width = -5;
16. self.navigationItem.rightBarButtonItems = [NSArray arrayWithObjects:negativeSpacer, btn_right, nil];
17. [btn_right release];

再看一个例子：

UIButton *btnBack = [UIButton
buttonWithType:UIButtonTypeCustom];

btnBack.frame =
CGRectMake(0,
0, 23,
23);

btnBack.backgroundColor = [UIColor
clearColor];

[btnBack setImage:[UIImage
imageNamed:@"bar_back_nomal.png"]
forState:UIControlStateNormal];

[btnBack setImage:[UIImage
imageNamed:@"bar_back_selected.png"]
forState:UIControlStateHighlighted];

[btnBack setImage:[UIImage
imageNamed:@"bar_back_selected.png"]
forState:UIControlStateSelected];

[btnBack addTarget:self
action:@selector(btnBackClicked:)
forControlEvents:UIControlEventTouchUpInside];

[self.navigationItem
setLeftBarButtonItem:[[UIBarButtonItem
alloc]initWithCustomView:btnBack]];

UIButton * source = [UIButton
buttonWithType:UIButtonTypeCustom];

source.frame =
CGRectMake(0,
0, 35,
35);

source.backgroundColor = [UIColor
clearColor];

[source setImage:[UIImage
imageNamed:@"head_normal.png"]
forState:UIControlStateNormal];

[source setImage:[UIImage
imageNamed:@"head_press.png"]
forState:UIControlStateHighlighted];

[source setImage:[UIImage
imageNamed:@"head_press.png"]
forState:UIControlStateSelected];

[source addTarget:self
action:@selector(btnPublicNum:)
forControlEvents:UIControlEventTouchUpInside];

UIBarButtonItem * btn_right = [[UIBarButtonItem
alloc]initWithCustomView:source];

UIBarButtonItem * negativeSpacer = [[UIBarButtonItem
alloc]initWithBarButtonSystemItem:UIBarButtonSystemItemFixedSpace
target:nil
action:nil];

negativeSpacer.width = -6;

self.navigationItem.rightBarButtonItems = [NSArray
arrayWithObjects:negativeSpacer, btn_right,
nil];

OK：左右边界一模一样