UITextView自动换行，自适应高度

NSString *str = @“eeiieieie”;
UITextView *textView = [[UITextView alloc] init];
[self.view addSubview:textView];
textView.backgroundColor = [UIColor clearColor];
textView.text = str;
textView.scrollEnabled = YES;
textView.font = [UIFont systemFontOfSize:14];
CGSize size = [str sizeWithFont: font  constrainedToSize:CGSizeMake(320,500) lineBreakMode:UILineBreakModeWordWrap];
 [label setFrame:CGRectMake(0, 20, size.width, size.height)];
 textView.userInteractionEnabled = NO;
 textView.autoresizingMask = UIViewAutoresizingFlexibleHeight;