当我加载一个UIView时,我如何在iPhone SDK上设置UITextField的最大字符数?
当前回答
这是处理UITextField最大长度的正确方法,它允许返回键退出辞职文本字段作为第一响应器,并让用户在达到限制时退格
- (BOOL)textField:(UITextField *)textField shouldChangeCharactersInRange:(NSRange)range replacementString:(NSString *)string {
int MAX_LENGHT = 5;
if([string isEqualToString:@"\n"])
{
[textField resignFirstResponder];
return FALSE;
}
else if(textField.text.length > MAX_LENGHT-1)
{
if([string isEqualToString:@""] && range.length == 1)
{
return TRUE;
}
else
{
return FALSE;
}
}
else
{
return TRUE;
}
}
其他回答
把它压缩到一行代码:)
将文本视图的委托设置为“self”,然后在你的.h中添加<UITextViewDelegate>,在你的.m中添加以下代码....你可以调整数字“7”为任何你想要的最大字符数。
-(BOOL)textView:(UITextView *)a shouldChangeTextInRange:(NSRange)b replacementText:(NSString *)c {
return ((a.text.length+c.length<=7)+(c.length<1)+(b.length>=c.length)>0);
}
这段代码负责输入新字符、删除字符、选择字符然后输入或删除、选择字符并剪切、粘贴,以及选择字符并粘贴。
完成了!
另外,用位操作编写这段代码的另一种很酷的方法是
-(BOOL)textView:(UITextView *)a shouldChangeTextInRange:(NSRange)b replacementText:(NSString *)c {
return 0^((a.text.length+c.length<=7)+(c.length<1)+(b.length>=c.length));
}
谢谢你奥古斯特!(Post)
这是我最终得到的代码:
#define MAX_LENGTH 20
- (BOOL)textField:(UITextField *)textField shouldChangeCharactersInRange:(NSRange)range replacementString:(NSString *)string
{
if (textField.text.length >= MAX_LENGTH && range.length == 0)
{
return NO; // return NO to not change text
}
else
{return YES;}
}
我已经实现了一个UITextField扩展,以添加一个maxLength属性。
它基于Xcode 6 IBInspectables,所以你可以在接口构建器上设置maxLength限制。
实现如下:
UITextField + MaxLength。h
#import <UIKit/UIKit.h>
@interface UITextField_MaxLength : UITextField<UITextFieldDelegate>
@property (nonatomic)IBInspectable int textMaxLength;
@end
UITextField + MaxLength。m
#import "UITextField+MaxLength.h"
@interface UITextField_MaxLength()
@property (nonatomic, assign) id <UITextFieldDelegate> superDelegate;
@end
@implementation UITextField_MaxLength
- (BOOL)textField:(UITextField *) textField shouldChangeCharactersInRange:(NSRange)range replacementString:(NSString *)string {
//validate the length, only if it's set to a non zero value
if (self.textMaxLength>0) {
if(range.length + range.location > textField.text.length)
return NO;
if (textField.text.length+string.length - range.length>self.textMaxLength) {
return NO;
}
}
//if length validation was passed, query the super class to see if the delegate method is implemented there
if (self.superDelegate && [self.superDelegate respondsToSelector:@selector(textField:shouldChangeCharactersInRange:replacementString:)]) {
return [self.superDelegate textField:textField shouldChangeCharactersInRange:range replacementString:string];
}
else{
//if the super class does not implement the delegate method, simply return YES as the length validation was passed
return YES;
}
}
- (void)setDelegate:(id<UITextFieldDelegate>)delegate {
if (delegate == self)
return;
self.superDelegate = delegate;
[super setDelegate:self];
}
//forward all non overriden delegate methods
- (id)forwardingTargetForSelector:(SEL)aSelector {
if ([self.superDelegate respondsToSelector:aSelector])
return self.superDelegate;
return [super forwardingTargetForSelector:aSelector];
}
- (BOOL)respondsToSelector:(SEL)aSelector {
if ([self.superDelegate respondsToSelector:aSelector])
return YES;
return [super respondsToSelector:aSelector];
}
@end
最好的方法是设置文本更改通知。在视图控制器方法的-awakeFromNib中,你需要:
[[NSNotificationCenter defaultCenter] addObserver:self selector:@selector(limitTextField:) name:@"UITextFieldTextDidChangeNotification" object:myTextField];
然后在同一个类中添加:
- (void)limitTextField:(NSNotification *)note {
int limit = 20;
if ([[myTextField stringValue] length] > limit) {
[myTextField setStringValue:[[myTextField stringValue] substringToIndex:limit]];
}
}
然后链接出口myTextField到你的UITextField,它将不让你添加任何字符后,你达到限制。一定要把这个添加到你的dealloc方法中:
[[NSNotificationCenter defaultCenter] removeObserver:self name:@"UITextFieldTextDidChangeNotification" object:myTextField];
下面的代码类似于sickp的答案,但是正确地处理复制-粘贴操作。如果尝试粘贴超过限制的文本,下面的代码将截断文本以符合限制,而不是完全拒绝粘贴操作。
- (BOOL)textField:(UITextField *)textField shouldChangeCharactersInRange:(NSRange)range replacementString:(NSString *)string {
static const NSUInteger limit = 70; // we limit to 70 characters
NSUInteger allowedLength = limit - [textField.text length] + range.length;
if (string.length > allowedLength) {
if (string.length > 1) {
// get at least the part of the new string that fits
NSString *limitedString = [string substringToIndex:allowedLength];
NSMutableString *newString = [textField.text mutableCopy];
[newString replaceCharactersInRange:range withString:limitedString];
textField.text = newString;
}
return NO;
} else {
return YES;
}
}
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