将 UITextField 增加到一定长度

我有一个 UITextField，我想“自动”调整其边界大小，以便为字段中添加的字符串腾出空间。但是，我希望它的宽度达到一定程度的最大值。我可以采取的最佳方法是什么？

谢谢你的帮助。

EDIT:

测试视图.h

#import <UIKit/UIKit.h>


@interface TestingView : UIView <UITextFieldDelegate> {

}

@end

测试视图.m

#import "TestingView.h"


@implementation TestingView

- (void)awakeFromNib
{
    CGRect testingBounds = self.bounds;

    testingBounds.size.width = testingBounds.size.width - 20;

    testingBounds.size.height = 30;

    CGPoint testingCenter = self.center;

    testingCenter.y = testingCenter.y - 75;

    UITextField *testingField = [[UITextField alloc] initWithFrame:testingBounds];

    testingField.center = testingCenter;

    testingField.delegate = self;

    testingField.placeholder = @"Testing";

    [self addSubview:testingField];
}

- (BOOL)textField:(UITextField *)textField shouldChangeCharactersInRange:(NSRange)range replacementString:(NSString *)string
{
    int yourMaxWidth = 150;

    float width = [textField.text sizeWithFont:
                   [UIFont systemFontOfSize: 14]  
                                 constrainedToSize:
                   CGSizeMake(yourMaxWidth, textField.bounds.size.height)].width;

    textField.bounds = CGRectMake(textField.bounds.origin.x,
                                      textField.bounds.origin.y,
                                      width, 
                                      textField.bounds.size.height);

    return YES;
}
@end

在委托方法中文本字段：shouldChangeCharactersInRange：替换字符串： http://developer.apple.com/iphone/library/documentation/uikit/reference/UITextFieldDelegate_Protocol/UITextFieldDelegate/UITextFieldDelegate.html#//apple_ref/occ/intfm/UITextFieldDelegate/textField:shouldChangeCharactersInRange:replacementString:你应该测量你的UITextField的文本大小使用sizeWithFont:constrainedToSize: http://developer.apple.com/iphone/library/documentation/UIKit/Reference/NSString_UIKit_Additions/Reference/Reference.html#//apple_ref/occ/instm/NSString/sizeWithFont:constrainedToSize:并使用返回的CGSize的宽度参数来设置你的UITextField的边界宽度。

- (BOOL)textField:(UITextField *)textField shouldChangeCharactersInRange:(NSRange)range replacementString:(NSString *)string
{
    float width = [yourTextField.text sizeWithFont:
           [UIFont systemFontOfSize: 14]  
                                      constrainedToSize:
           CGSizeMake(yourMaxWidth, yourTextField.bounds.size.height)].width;

    yourTextField.bounds = CGRectMake(yourTextField.bounds.origin.x,
                                      yourTextField.bounds.origin.y,
                                      width, 
                                      yourTextField.bounds.size.height);
}