iOS navigationController的title实现

1.设置题目内容

self.title = @"我是题目我是题目我是题目我是题目我是题目我是题目我是题目我是题目我是题目我是题目我是题目我是题目我是题目我是题目我是题目";

2.用NSMutableParagraphStyle设置NSLineBreakByTruncatingMiddle

NSMutableParagraphStyle *paragraphStyle = [[NSMutableParagraphStyle alloc] init];
paragraphStyle.lineBreakMode = NSLineBreakByTruncatingMiddle;

3.设置titleTextAttributes

self.navigationController.navigationBar.titleTextAttributes = @{NSParagraphStyleAttributeName:paragraphStyle};

附各种省略的样式

typedef NS_ENUM(NSInteger, NSLineBreakMode) {
    NSLineBreakByWordWrapping = 0,         // Wrap at word boundaries, default
    NSLineBreakByCharWrapping,        // Wrap at character boundaries
    NSLineBreakByClipping,        // Simply clip
    NSLineBreakByTruncatingHead,    // Truncate at head of line: "...wxyz"
    NSLineBreakByTruncatingTail,    // Truncate at tail of line: "abcd..."
    NSLineBreakByTruncatingMiddle    // Truncate middle of line:  "ab...yz"
} API_AVAILABLE(macos(10.0), ios(6.0), watchos(2.0), tvos(9.0));