默認UILabel是垂直居中對齊的,如果你的UILabel高度有多行,當內容少的時候,會自動垂直居中。
方法
1. 在顯示文字時,首先計算顯示當前的文字需要多寬和多高,然後將對應的UILabel的大小改變成對應的寬度和高度
CGSize maximumSize = CGSizeMake(300, 1);
NSString *dateString = @"day by day one more";
UIFont *dateFont = [UIFont fontWithName:@"Helvetica" size:14];
CGSize dateStringSize = [dateString sizeWithFont:dateFont
constrainedToSize:maximumSize
lineBreakMode:self.dateLabel.lineBreakMode];
CGRect dateFrame = CGRectMake(10, 10, 300, dateStringSize.height);
self.dateLabel.frame = dateFrame;
2.此方法更加簡單粗暴,但是很有效。其方法是在文本後面加多一些\n。
需要注意的是,\n後還得加至少一個空格,否則多餘的\n會被UILabel忽略。
for(int i=0; i<newLinesToPad; i++)
self.text = [self.text stringByAppendingString:@"\n "];
3.最正統的方法,利用objective-c的category特性,修改UILabel的繪製代碼。
// -- file: UILabel+VerticalAlign.h
#pragma mark VerticalAlign
@interface UILabel (VerticalAlign)
- (void)alignTop;
- (void)alignBottom;
@end
// -- file: UILabel+VerticalAlign.m
@implementation UILabel (VerticalAlign)
- (void)alignTop {
CGSize fontSize = [self.text sizeWithFont:self.font];
double finalHeight = fontSize.height * self.numberOfLines;
double finalWidth = self.frame.size.width; //expected width of label
CGSize theStringSize = [self.text sizeWithFont:self.font constrainedToSize:CGSizeMake(finalWidth, finalHeight) lineBreakMode:self.lineBreakMode];
int newLinesToPad = (finalHeight - theStringSize.height) / fontSize.height;
for(int i=0; i<newLinesToPad; i++)
self.text = [self.text stringByAppendingString:@"\n "];
}
- (void)alignBottom {
CGSize fontSize = [self.text sizeWithFont:self.font];
double finalHeight = fontSize.height * self.numberOfLines;
double finalWidth = self.frame.size.width; //expected width of label
CGSize theStringSize = [self.text sizeWithFont:self.font constrainedToSize:CGSizeMake(finalWidth, finalHeight) lineBreakMode:self.lineBreakMode];
int newLinesToPad = (finalHeight - theStringSize.height) / fontSize.height;
for(int i=0; i<newLinesToPad; i++)
self.text = [NSString stringWithFormat:@" \n%@",self.text];
}
@end