UILabel *label = [[UILabel alloc] initWithFrame:CGRectMake(0,0,0,0)];//后面还会重新设置其size。

[label setNumberOfLines:0];

NSString *s = @"string......";

UIFont *font = [UIFont fontWithName:@"Arial" size:12];

CGSize size = CGSizeMake(320,2000);

CGSize labelsize = [s sizeWithFont:font constrainedToSize:sizelineBreakMode:UILineBreakModeWordWrap];

[label setFrame:CGRectMake(0, 0, labelsize.width, labelsize.height)];

[self.view addSubView:label];

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