限制 Text Field 输入的内容类型：只允许输入数字

效果如下：

 

ViewController.h

#import <UIKit/UIKit.h>

@interface ViewController : UIViewController<UITextFieldDelegate>
@property (strong, nonatomic) IBOutlet UITextField *txtLimitInput;

@end

ViewController.m

#import "ViewController.h"

@interface ViewController ()
- (void)layoutUI;
- (BOOL)validateNumberByASCII:(NSString *)string;
- (BOOL)validateNumberByRange:(NSString *)string;
- (BOOL)validateNumberByRegExp:(NSString *)string;
@end

@implementation ViewController

- (void)viewDidLoad {
    [super viewDidLoad];
    
    [self layoutUI];
}

- (void)didReceiveMemoryWarning {
    [super didReceiveMemoryWarning];
    // Dispose of any resources that can be recreated.
}

- (void)layoutUI {
    _txtLimitInput.placeholder = @"请输入数字";
    
    //第一种方式：设置键盘类型
    //_txtLimitInput.keyboardType = UIKeyboardTypeDecimalPad;
    
    //第二种方式：通过 UITextFieldDelegate 的 shouldChangeCharactersInRange: 方法
    _txtLimitInput.delegate = self;
}

#pragma mark - 三种判断字符串内容是否是有效数字的方式
/**
 *  『ASCII码』判断字符串内容是否是有效数字
 *
 *  @param string 需要验证的字符串
 *
 *  @return 字符串内容是否是有效数字
 */
- (BOOL)validateNumberByASCII:(NSString *)string {
    BOOL isValid = YES;
    NSUInteger len = string.length;
    if (len > 0) {
        for (NSUInteger i=0; i<len; i++) {
            NSUInteger asciiCode = [string characterAtIndex:i];
            if (asciiCode < 48 || asciiCode > 57) {
                isValid = NO;
                break;
            }
        }
    }
    return isValid;
}

/**
 *  『字符范围』判断字符串内容是否是有效数字
 *
 *  @param string 需要验证的字符串
 *
 *  @return 字符串内容是否是有效数字
 */
- (BOOL)validateNumberByRange:(NSString *)string {
    BOOL isValid = YES;
    NSUInteger len = string.length;
    if (len > 0) {
        NSCharacterSet *validNumberCS = [NSCharacterSet characterSetWithCharactersInString:@"0123456789"];
        NSUInteger singleStrIndex = 0;
        do {
            NSString *singleStr = [string substringWithRange:NSMakeRange(singleStrIndex, 1)];
            NSRange range = [singleStr rangeOfCharacterFromSet:validNumberCS];
            if (range.length == 0) {
                isValid = NO;
                break;
            }
            singleStrIndex++;
        } while (singleStrIndex < len);
    }
    return isValid;
}

/**
 *  『正则表达式；推荐使用，不用循环遍历，控制更灵活』判断字符串内容是否是有效数字
 *
 *  @param string 需要验证的字符串
 *
 *  @return 字符串内容是否是有效数字
 */
- (BOOL)validateNumberByRegExp:(NSString *)string {
    BOOL isValid = YES;
    NSUInteger len = string.length;
    if (len > 0) {
        NSString *numberRegex = @"^[0-9]*$";
        NSPredicate *numberPredicate = [NSPredicate predicateWithFormat:@"SELF MATCHES %@", numberRegex];
        isValid = [numberPredicate evaluateWithObject:string];
    }
    return isValid;
}

#pragma mark - UITextFieldDelegate
- (BOOL)textField:(UITextField *)textField shouldChangeCharactersInRange:(NSRange)range replacementString:(NSString *)string {
    //return [self validateNumberByASCII:string];
    //return [self validateNumberByRange:string];
    return [self validateNumberByRegExp:string]; //推荐方式
}

@end

Main.storyboard

<?xml version="1.0" encoding="UTF-8" standalone="no"?>
<document type="com.apple.InterfaceBuilder3.CocoaTouch.Storyboard.XIB" version="3.0" toolsVersion="7706" systemVersion="14E46" targetRuntime="iOS.CocoaTouch" propertyAccessControl="none" useAutolayout="YES" useTraitCollections="YES" initialViewController="vXZ-lx-hvc">
    <dependencies>
        <deployment identifier="iOS"/>
        <plugIn identifier="com.apple.InterfaceBuilder.IBCocoaTouchPlugin" version="7703"/>
    </dependencies>
    <scenes>
        <!--View Controller-->
        <scene sceneID="ufC-wZ-h7g">
            <objects>
                <viewController id="vXZ-lx-hvc" customClass="ViewController" sceneMemberID="viewController">
                    <layoutGuides>
                        <viewControllerLayoutGuide type="top" id="jyV-Pf-zRb"/>
                        <viewControllerLayoutGuide type="bottom" id="2fi-mo-0CV"/>
                    </layoutGuides>
                    <view key="view" contentMode="scaleToFill" id="kh9-bI-dsS">
                        <rect key="frame" x="0.0" y="0.0" width="600" height="600"/>
                        <autoresizingMask key="autoresizingMask" flexibleMaxX="YES" flexibleMaxY="YES"/>
                        <subviews>
                            <textField opaque="NO" clipsSubviews="YES" contentMode="scaleToFill" contentHorizontalAlignment="left" contentVerticalAlignment="center" borderStyle="roundedRect" minimumFontSize="17" translatesAutoresizingMaskIntoConstraints="NO" id="mb3-C5-UpN">
                                <rect key="frame" x="200" y="285" width="200" height="30"/>
                                <constraints>
                                    <constraint firstAttribute="width" constant="200" id="8dl-R0-OzV"/>
                                </constraints>
                                <fontDescription key="fontDescription" type="system" pointSize="14"/>
                                <textInputTraits key="textInputTraits"/>
                            </textField>
                            <label opaque="NO" userInteractionEnabled="NO" contentMode="left" horizontalHuggingPriority="251" verticalHuggingPriority="251" text="限制 Text Field 输入的内容类型" lineBreakMode="tailTruncation" baselineAdjustment="alignBaselines" adjustsFontSizeToFit="NO" translatesAutoresizingMaskIntoConstraints="NO" id="8zf-7E-ija">
                                <rect key="frame" x="200" y="255" width="196" height="17"/>
                                <fontDescription key="fontDescription" type="system" pointSize="14"/>
                                <color key="textColor" red="0.0" green="0.0" blue="0.0" alpha="1" colorSpace="calibratedRGB"/>
                                <nil key="highlightedColor"/>
                            </label>
                        </subviews>
                        <color key="backgroundColor" white="1" alpha="1" colorSpace="custom" customColorSpace="calibratedWhite"/>
                        <constraints>
                            <constraint firstItem="mb3-C5-UpN" firstAttribute="centerX" secondItem="kh9-bI-dsS" secondAttribute="centerX" id="Dh5-bw-2LN"/>
                            <constraint firstItem="mb3-C5-UpN" firstAttribute="centerY" secondItem="kh9-bI-dsS" secondAttribute="centerY" id="Lby-hq-mya"/>
                            <constraint firstItem="mb3-C5-UpN" firstAttribute="leading" secondItem="8zf-7E-ija" secondAttribute="leading" id="SyI-SC-iNN"/>
                            <constraint firstItem="mb3-C5-UpN" firstAttribute="top" secondItem="8zf-7E-ija" secondAttribute="bottom" constant="13" id="yuO-kC-OCZ"/>
                        </constraints>
                    </view>
                    <connections>
                        <outlet property="txtLimitInput" destination="mb3-C5-UpN" id="cYi-Ep-sWq"/>
                    </connections>
                </viewController>
                <placeholder placeholderIdentifier="IBFirstResponder" id="x5A-6p-PRh" sceneMemberID="firstResponder"/>
            </objects>
        </scene>
    </scenes>
</document>