iOS UITextField最大字符数和字节数的限制详解

前言

这里我给大家几组测试用例可以一试，为啥不好用。

     1、限制10个字节，输入2个emoj之后是8个字节(一个emoj是4个字节)，此时再输入一个中文，看看结果如何(中文的utf8占3个字节)

     2、限制5个字符,一个emoj是2个字符,其他都是一个。此时输入两个emoj，再输入中文，然后中文联想试试。

就目前的情况来说，看了很多资料，并没有一个通用的能限制字符数和字节数的封装。这里全面进行了总结，并进行了封装。欢迎大家下载。

一. 字符限制

1. 错误方法

常见的这种方法是错误的，会导致emoj表情的截取问题

- (bool)textfield:(uitextfield *)textfield shouldchangecharactersinrange:(nsrange)range replacementstring:(nsstring *)string
{
 if(range.length + range.location > textfield.text.length)
 {
 return no;
 }
 
 nsuinteger newlength = [textfield.text length] + [string length] - range.length;
 return newlength <= 5;
}

这种限制方法会导致拼音下出现这种情况，且无法输入.无法输入满5个字符。在emoj表情也有问题

2. 推荐方法

使用rangeofcomposedcharactersequencesforrange, 防止在range范围内整词被截断

- (void)textfielddidchange:(uitextfield *)textfield
{
 nsstring *tobestring = textfield.text;

 uitextrange *selectedrange = [textfield markedtextrange];
 uitextposition *position = [textfield positionfromposition:selectedrange.start offset:0];
 
 // 没有高亮选择的字，则对已输入的文字进行字数统计和限制,防止中文被截断
 if (!position){
 if (tobestring.length > _maxlength){
  //中文和emoj表情存在问题，需要对此进行处理
  nsrange rangerange = [tobestring rangeofcomposedcharactersequencesforrange:nsmakerange(0, _maxlength)];
  textfield.text = [tobestring substringwithrange:rangerange];
 }
 }
}

二. 字节限制

1. 限制字节数

在utf8中，英文和数字是1个字节,汉子是3个字节，emoji是3或者4个字节。这里的难度比上面更大，如果截取失败，极有可能出现乱码。这里我们的做法如下

- (void)textfielddidchange:(uitextfield *)textfield
{
 nsstring *tobestring = textfield.text;
 //---字节处理
 nsinteger bytescount = strlen([textfield.text utf8string]);
 if (bytescount > _maxbyteslength) {
 nsstring *content = [textfield.text substrwithutf8len:(int)_maxbyteslength];
 textfield.text = content;
 }
}

- (bool)textfield:(uitextfield *)textfield shouldchangecharactersinrange:(nsrange)range replacementstring:(nsstring *)string{
 
 nsstring * inputstring = [textfield.text stringbyreplacingcharactersinrange:range withstring:string];
 
 //限制字节数
 if ([inputstring length] > 0){
 nsinteger len = strlen([inputstring utf8string]);
 if (len > _maxbyteslength){
  return no;
 }
 else {
  return yes;
 }
 }
 return yes;
}

这里不能只在进行限制，在textfielddidchange中需要对中文联想做处理才行

三. 放弃键盘

1. 能拿到uitextfield的时候用

- (bool)textfieldshouldreturn:(uitextfield *)textfield
{
 return [textfield resignfirstresponder];
}

2. 点击view消失的时候用

[self.view endediting:yes];

3. 难以获取的时候用

[[uiapplication sharedapplication] sendaction:@selector(resignfirstresponder) to:nil from:nil forevent:nil];

或者

[[[uiapplication sharedapplication] keywindow] endediting:yes];

4.tableview点击空白处或者滚动时消失

{
 uitapgesturerecognizer *singletap = [[uitapgesturerecognizer alloc] initwithtarget:self action:@selector(fingertapped:)];
 [self.view addgesturerecognizer:singletap];
}

#pragma mark- 键盘消失
-(void)fingertapped:(uitapgesturerecognizer *)gesturerecognizer{
 [self.view endediting:yes];
}
-(void)scrollviewwillbegindragging:(uiscrollview *)scrollview{
 [self.view endediting:yes];
}

四. 正则表达式限制

请参考 正则表达式语法表 ,这里我提供了两种表达式给大家参考，一个int,一个无unsignedint

-(bool) istextfieldmatchwithregularexpression:(nsstring *)exporession{
 
 nspredicate *predicate = [nspredicate predicatewithformat:@"self matches %@",exporession];
 return [predicate evaluatewithobject:self];
}
-(bool) istextfieldintvalue{
 return [self istextfieldmatchwithregularexpression:@"[-]{0,1}[0-9]*"];
}
-(bool) istextfieldunsignedintvalue{
 return [self istextfieldmatchwithregularexpression:@"[0-9]+"];
}

五. uitextfield的键盘事件多次回调问题

1.键盘高度遮挡问题

一般出现遮挡的时候我们用以下代码,看看当前textfield是否在键盘下面，在的话算出键盘的顶端和textfield的底部的距离，然后做偏移动画

- (void)keyboardwillshow:(nsnotification *)notification {
 
 nsdictionary *userinfo = [notification userinfo];
 
 nsvalue* avalue = [userinfo objectforkey:uikeyboardframeenduserinfokey];
 cgrect keyboardrect = [avalue cgrectvalue];
 keyboardrect = [self.view convertrect:keyboardrect fromview:nil];
 
 cgfloat keyboardtop = keyboardrect.origin.y;
 
 cgfloat offset = self.normaltextfield.frame.size.height + self.normaltextfield.frame.origin.y - keyboardtop;
 
 nsvalue *animationdurationvalue = [userinfo objectforkey:uikeyboardanimationdurationuserinfokey];
 nstimeinterval animationduration;
 [animationdurationvalue getvalue:&animationduration];
 
 if(offset > 0){
 // animate the resize of the text view's frame in sync with the keyboard's appearance.
 [uiview beginanimations:nil context:null];
 [uiview setanimationduration:animationduration];

 cgrect rect = cgrectmake(0.0f, -offset,self.view.frame.size.width,self.view.frame.size.height);
 self.view.frame = rect;
 [uiview commitanimations];
 }
}

1、真机

如果使用了中文输入法，注册的keyboardwillshow会回调两次。第一次是键盘默认高度216，第二次则是加了keyboard的导航栏的高度。

2、模拟器

第一次弹出键盘没有问题

打印userinfo:

(lldb) po userinfo
{
 uikeyboardanimationcurveuserinfokey = 7;
 uikeyboardanimationdurationuserinfokey = "0.25";
 uikeyboardboundsuserinfokey = "nsrect: {{0, 0}, {414, 226}}";
 uikeyboardcenterbeginuserinfokey = "nspoint: {207, 849}";
 uikeyboardcenterenduserinfokey = "nspoint: {207, 623}";
 uikeyboardframebeginuserinfokey = "nsrect: {{0, 736}, {414, 226}}";
 uikeyboardframeenduserinfokey = "nsrect: {{0, 510}, {414, 226}}";
 uikeyboardislocaluserinfokey = 1;
}

此时我们去按123旁边的小圆球会出现如下的图：

打印userinfo:

(lldb) po userinfo
{
 uikeyboardanimationcurveuserinfokey = 7;
 uikeyboardanimationdurationuserinfokey = "0.25";
 uikeyboardboundsuserinfokey = "nsrect: {{0, 0}, {414, 271}}";
 uikeyboardcenterbeginuserinfokey = "nspoint: {207, 623}";
 uikeyboardcenterenduserinfokey = "nspoint: {207, 600.5}";
 uikeyboardframebeginuserinfokey = "nsrect: {{0, 510}, {414, 226}}";
 uikeyboardframeenduserinfokey = "nsrect: {{0, 465}, {414, 271}}";
 uikeyboardislocaluserinfokey = 1;
}

键盘被遮挡了。

总结:观察结果,发现了这个规律，打印一下时间,还有一个问题就是，中文键盘第一次启动的时候会回调两次。

keyboardrect = [self.view convertrect:keyboardrect fromview:nil];

所以去掉这句话即可

六. 使用封装的xxtextfield

uitextview , uitextfield 中如果有keyboard的时候，需要一个自动弹起事件，以及弹起之后的content的偏移对父view的处理。如果每个页面都实现一次会非常复杂。这里我们介绍一种自动化的处理机制。在此之前，先介绍一下文字处理框架.最后给大家推荐一下我写的 xxtextfield ,大家也可以在此基础上自己添加一些正则表达式。

1.解决uiview中的textfield 遮挡问题

_textfieldname.keyboardtype = uikeyboardtypedefault;
_textfieldname.inputtype = xxtextfieldtypeonlyint;
_textfieldname.maxlength = 5;
_textfieldpwd.inputtype = xxtextfieldtypeforbidemoj;

#import "xxkeyboardmanager.h"
@interface xxcorrectvc ()<xxkeyboardmanagershowhiddennotificationdelegate>
@end

@implementation xxcorrectvc

- (void)viewdidload {
 [super viewdidload];
 [[xxkeyboardmanager sharedinstance] setdelegate:self];
 // do any additional setup after loading the view from its nib.
}
#pragma mark- keyboardshow/hidden
- (void)showkeyboardwithrect:(cgrect)keyboardrect
    withduration:(cgfloat)animationduration
{
 cgfloat offset = self.textfieldcorrect.frame.size.height + self.textfieldcorrect.frame.origin.y - keyboardrect.origin.y;
 if(offset < 0){
  return;
 }
 [uiview animatewithduration:animationduration
       delay:0.f
      options:uiviewanimationoptioncurveeaseinout animations:^{
  cgrect rect = cgrectmake(0.0f, -offset,self.view.frame.size.width,self.view.frame.size.height);
  self.view.frame = rect;
 } completion:^(bool finished) {
  
 }];
}

- (void)hiddenkeyboardwithrect:(cgrect)keyboardrect
     withduration:(cgfloat)animationduration
{
 [uiview animatewithduration:animationduration
       delay:0.f
      options:uiviewanimationoptioncurveeaseinout animations:^{
  self.textfieldcorrect.frame = self.view.bounds;
 } completion:^(bool finished) {
 }];
}
@end

2.解决uitableview中键盘遮挡问题

/*
 * 键盘要显示的时候
 */
- (void)showkeyboardwithrect:(cgrect)keyboardrect
    withduration:(cgfloat)animationduration{
 
 cgsize kbsize = keyboardrect.size;
 
 uiedgeinsets contentinsets = uiedgeinsetsmake(0.0, 0.0, kbsize.height, 0.0);
 _basetableview.contentinset = contentinsets;
 _basetableview.scrollindicatorinsets = contentinsets;
 
 // if active text field is hidden by keyboard, scroll it so it's visible
 // your app might not need or want this behavior.
 cgrect arect = self.view.frame;
 arect.size.height -= kbsize.height;
 
 if (!cgrectcontainspoint(arect, _activecell.frame.origin) ) {
  [_basetableview scrollrecttovisible:_activecell.frame animated:yes];
 }
}

/*
 * 键盘要消失的时候
 */
- (void)hiddenkeyboardwithrect:(cgrect)keyboardrect
     withduration:(cgfloat)animationduration{
 _basetableview.contentinset = uiedgeinsetszero;
 _basetableview.scrollindicatorinsets = uiedgeinsetszero;
}

总结

以上就是这篇文章的全部内容了，希望本文的内容对各位android开发者们能有所帮助，如果有疑问大家可以留言交流。