详解UILabel的adjustsFontSizeToFitWidth值

UILabel有一个属性值，叫adjustsFontSizeToFitWidth，看着名字就知道，他是用来让文字自动适应UILabel宽度的。

先看看显示效果：

测试用源码：

//
//  RootViewController.m
//  Letters
//
//  Created by YouXianMing on 14-9-14.
//  Copyright (c) 2014年 YouXianMing. All rights reserved.
//

#import "RootViewController.h"

@interface RootViewController ()

@end

@implementation RootViewController

- (void)viewDidLoad
{
    [super viewDidLoad];

    {
        UILabel *label                  = [[UILabel alloc] initWithFrame:CGRectMake(0, 0, 250, 30)];
        label.layer.borderWidth         = 1.f;
        CGPoint point                   = self.view.center;
        point.y                         = 70;
        label.center                    = point;
        label.text                      = @"YouXianMing NoZuoNoDie";
        label.textAlignment             = NSTextAlignmentCenter;
        label.adjustsFontSizeToFitWidth = YES;
        label.baselineAdjustment        = UIBaselineAdjustmentAlignCenters;
        [self.view addSubview:label];
    }

    {
        UILabel *label                  = [[UILabel alloc] initWithFrame:CGRectMake(0, 0, 200, 30)];
        label.layer.borderWidth         = 1.f;
        CGPoint point                   = self.view.center;
        point.y                         = 120;
        label.center                    = point;
        label.text                      = @"YouXianMing NoZuoNoDie";
        label.textAlignment             = NSTextAlignmentCenter;
        label.adjustsFontSizeToFitWidth = YES;
        label.baselineAdjustment        = UIBaselineAdjustmentAlignCenters;
        [self.view addSubview:label];
    }

    {
        UILabel *label                  = [[UILabel alloc] initWithFrame:CGRectMake(0, 0, 150, 30)];
        label.layer.borderWidth         = 1.f;
        CGPoint point                   = self.view.center;
        point.y                         = 170;
        label.center                    = point;
        label.text                      = @"YouXianMing NoZuoNoDie";
        label.textAlignment             = NSTextAlignmentCenter;
        label.adjustsFontSizeToFitWidth = YES;
        label.baselineAdjustment        = UIBaselineAdjustmentAlignCenters;
        [self.view addSubview:label];
    }

    {
        UILabel *label                  = [[UILabel alloc] initWithFrame:CGRectMake(0, 0, 100, 30)];
        label.layer.borderWidth         = 1.f;
        CGPoint point                   = self.view.center;
        point.y                         = 220;
        label.center                    = point;
        label.text                      = @"YouXianMing NoZuoNoDie";
        label.textAlignment             = NSTextAlignmentCenter;
        label.adjustsFontSizeToFitWidth = YES;
        label.baselineAdjustment        = UIBaselineAdjustmentAlignCenters;
        [self.view addSubview:label];
    }
}

@end

以下是核心代码：