在修正公司产品BUG的时候的代码片段，留作记录做好注释也方便其他人
NSString *tempStr = self.navigationController.navigationBar.topItem.title; //获取上一个页面的title
UIFont *font = [UIFont fontWithName:@"Helvetica" size:13.0];
CGSize singleLineStringSize = [tempStr sizeWithFont:font];
UIButton *gobackBtn = [[UIButton alloc] initWithFrame:CGRectMake(0, 0, singleLineStringSize.width*1.5, 30)];
[gobackBtn setBackgroundImage:[[UIImage imageNamed:@"BackBg.png"] stretchableImageWithLeftCapWidth:13 topCapHeight:0]forState:UIControlStateNormal];//拉伸背景图片以适应button
[gobackBtn addTarget:self action:@selector(goback:)forControlEvents:UIControlEventTouchDown];
[gobackBtn setTitle:tempStr forState:UIControlStateNormal];
[gobackBtn.titleLabel setFont:font];
[gobackBtn setTitleEdgeInsets:UIEdgeInsetsMake(0, 8, 0, 0)];//让button上的字偏移8个像素
gobackBtn.lineBreakMode=UILineBreakModeWordWrap|UILineBreakModeTailTruncation;//如果字数过长的话，后面加上省略号
gobackBtn.titleLabel.minimumFontSize=12.0;//设置button上的字体最小值
gobackBtn.titleLabel.adjustsFontSizeToFitWidth = YES;//自动缩小button上的字号
UIBarButtonItem *barItem =[[UIBarButtonItem alloc] initWithCustomView:gobackBtn];
[gobackBtn release];
self.navigationItem.leftBarButtonItem = barItem;
[barItem release];