iOS UILabel自動適應開度和高度

處理UILabel根據文字長度和大小自動適應寬度和高度

   //這個frame是初設的，沒關系，后面還會重新設置其size。
    UILabel *label = [[UILabel alloc] initWithFrame:CGRectMake(0,0,0,0)];
    label.numberOfLines = 0;
    label.backgroundColor = [UIColor clearColor];


NSDictionary *attributes = @{NSFontAttributeName:[UIFont systemFontOfSize:20],};

NSString *str = @"abcdefg你上課可是你的拿到了";
CGSize textSize = [str boundingRectWithSize:CGSizeMake(100, 100) options:NSStringDrawingTruncatesLastVisibleLine attributes:attributes context:nil].size;;

[label setFrame:CGRectMake(100, 100, textSize.width, textSize.height)];
label.textColor = [UIColor greenColor];
label.text = str;
[self.view addSubview:label];</pre>