iOS UILabel设置居上对齐，居中对齐，居下对齐

在iOS中默认的UILabel中的文字在竖直方向上仅仅能居中对齐，博主參考国外站点。从UILabel继承了一个新类，实现了居上对齐，居中对齐，居下对齐。详细例如以下：

1. //
2. //  myUILabel.h
3. //
4. //
5. //  Created by yexiaozi_007 on 3/4/13.
6. //  Copyright (c) 2013 yexiaozi_007. All rights reserved.
7. //
8. #import <UIKit/UIKit.h>
9. typedef enum
10. {
11. VerticalAlignmentTop = 0, // default
12. VerticalAlignmentMiddle,
13. VerticalAlignmentBottom,
14. } VerticalAlignment;
15. @interface myUILabel : UILabel
16. {
17. @private
18. VerticalAlignment _verticalAlignment;
19. }
20. @property (nonatomic) VerticalAlignment verticalAlignment;
21. @end

1. //
2. //  myUILabel.m
3. //
4. //
5. //  Created by yexiaozi_007 on 3/4/13.
6. //  Copyright (c) 2013 yexiaozi_007. All rights reserved.
7. //
8. #import "myUILabel.h"
9. @implementation myUILabel
10. @synthesize verticalAlignment = verticalAlignment_;
11. - (id)initWithFrame:(CGRect)frame {
12. if (self = [super initWithFrame:frame]) {
13. self.verticalAlignment = VerticalAlignmentMiddle;
14. }
15. return self;
16. }
17. - (void)setVerticalAlignment:(VerticalAlignment)verticalAlignment {
18. verticalAlignment_ = verticalAlignment;
19. [self setNeedsDisplay];
20. }
21. - (CGRect)textRectForBounds:(CGRect)bounds limitedToNumberOfLines:(NSInteger)numberOfLines {
22. CGRect textRect = [super textRectForBounds:bounds limitedToNumberOfLines:numberOfLines];
23. switch (self.verticalAlignment) {
24. case VerticalAlignmentTop:
25. textRect.origin.y = bounds.origin.y;
26. break;
27. case VerticalAlignmentBottom:
28. textRect.origin.y = bounds.origin.y + bounds.size.height - textRect.size.height;
29. break;
30. case VerticalAlignmentMiddle:
31. // Fall through.
32. default:
33. textRect.origin.y = bounds.origin.y + (bounds.size.height - textRect.size.height) / 2.0;
34. }
35. return textRect;
36. }
37. -(void)drawTextInRect:(CGRect)requestedRect {
38. CGRect actualRect = [self textRectForBounds:requestedRect limitedToNumberOfLines:self.numberOfLines];
39. [super drawTextInRect:actualRect];
40. }
41. @end

在使用时：

1. lbl_mylabel = [[myUILabel alloc] initWithFrame:CGRectMake(20, 50, 150, 600)];
2. UIColor *color = [UIColor colorWithPatternImage:[UIImage imageNamed:@"halfTransparent.png"]];//使用半透明图片作为label的背景色
3. lbl_mylabel.backgroundColor = color;
4. lbl_mylabel.textAlignment = UITextAlignmentLeft;
5. lbl_mylabel.textColor = UIColor.whiteColor;
6. lbl_mylabel.lineBreakMode = UILineBreakModeWordWrap;
7. lbl_mylabel.numberOfLines = 0;
8. [lbl_mylabel setVerticalAlignment:VerticalAlignmentTop];
9. [self addSubview:lbl_mylabel];