基于UIView实现UIKeyInput协议来实现输入框 TextView

之前有次需求是要求做cell内的输入框动态换行，顺便研究了一下UITextView的实现，核心是UIKeyInput协议，重写

- (BOOL)hasText {

- (void)insertText:(NSString *)text {

- (void)deleteBackward {

这三个方法来完成输入框。第一个方法判断是否有文字，第二个是插入文本是的回调，第三个方法是删除按钮按下时的回调。

整个输入框通过SGEditViewDelegate.h、SGEditView.h、SGEditView.m来实现。

SGEditViewDelegate.h

这个代理作用是模仿UITextView的部分协议方法，例如- (void)editViewDidChange:等等，在合适的时机调用。

#import <Foundation/Foundation.h>

@class SGEditView;

/// Delegate for SGEditView, response to various event called.
@protocol SGEditViewDelegate <NSObject>

/// When EditView did change its text and executed this method.
- (void)editViewDidChange: (SGEditView *)editView;

@optional

/// When EditView
- (BOOL)editViewShouldReturn: (SGEditView *)editView inChange: (NSString *)text;

/// When EditView become first responsder and the Keyboard was presented into scene, executed this method.
- (void)editViewDidBeginEditing: (SGEditView *)editView;

/// When EditView processd all tasks after the Keyboard finished typing. executed this method.
- (void)editViewDidEndEditing: (SGEditView *)editView;


@end

SGEditView.h

对外暴露一些属性，例如占位文字，文字间隙等等

#import <UIKit/UIKit.h>
#import "SGEditViewDelegate.h"

NS_ASSUME_NONNULL_BEGIN

/// Self define EditView likes UITextView but based on UIView.
@interface SGEditView : UIView

/// Delegate target.
@property (nonatomic, weak) NSObject<SGEditViewDelegate> *delegate;

@property (nonatomic, strong) NSString *placeholder;

@property (nonatomic, strong) NSString *text;

@property (nonatomic, strong) UIColor *textColor;

@property (nonatomic, strong) UIFont *font;

@property (nonatomic, assign) UIEdgeInsets textContainerInset;

@property (nonatomic, assign) BOOL isEnableEnterToLeave;

@end

NS_ASSUME_NONNULL_END

SGEditView.m

这里具体实现有些复杂，例如光标的位置计算就实现的有些问题，如果有读者平常业务是frame编写的就知道计算多行文字的末尾position是有多复杂，希望有经验的读者不吝赐教解决这个问题。

系统的UITextView输入框可以输入中文，但是中文存在候选文本，处理起来比较麻烦所以这里就没有实现。

具体实现原理就是：

touchBegin里面注册第一响应者调起键盘；
insertText方法里面在合适的时机把代理方法回调出去；
使用属性把文本保存起来，例如这里是用_text保存的；
调用[self setNeedsDisplay];把drawRect唤起；
在drawRect里面使用CF相关内容绘制文字，最后别忘了由于是调用的c代码，不要忘了手动释放内存。

#import "SGEditView.h"
#import <CoreText/CoreText.h>

static NSString * const path_text = @"text";

static NSString * const path_cursor_opacity = @"opacity";

@interface SGEditView ()<UIKeyInput>

@property (nonatomic, strong) UILabel *placeholderLabel;

@property (nonatomic, strong) UIView *cursor;

@property (nonatomic, strong) CABasicAnimation *cursorAnimation;

@property (nonatomic, readonly) BOOL canBecomeFirstResponder;

@end

@implementation SGEditView

- (instancetype)initWithFrame:(CGRect)frame {
    if (self = [super initWithFrame:frame]) {
        [self setupAttributes];
    }
    return self;
}

- (void)dealloc {
    [self removeObserver:self forKeyPath:path_text context:nil];
}

- (void)setupAttributes {
    self.text = @"";
    [self addSubview:self.placeholderLabel];
    [self addObserver:self forKeyPath:path_text options:NSKeyValueObservingOptionNew context:nil];
    
    [self addSubview:self.cursor];
    self.cursor.frame = CGRectMake(0, 0, 2, self.font.lineHeight);
    
}

- (void)touchesBegan:(NSSet<UITouch *> *)touches withEvent:(UIEvent *)event {
    [super touchesBegan:touches withEvent:event];
    if (self.canBecomeFirstResponder){
        [self becomeFirstResponder];
    }
}

- (void)observeValueForKeyPath:(NSString *)keyPath ofObject:(id)object change:(NSDictionary *)change context:(void *)context
{
    if ([keyPath isEqualToString:path_text]) {
        self.placeholderLabel.hidden = self.text.length > 0;

    }
}

- (void)drawRect:(CGRect)rect {
    [super drawRect:rect];
    
    CGRect insetRect = CGRectMake(rect.origin.x + self.textContainerInset.left,
                                  rect.origin.y - self.textContainerInset.top,
                                  rect.size.width - self.textContainerInset.left - self.textContainerInset.right,
                                  rect.size.height  - self.textContainerInset.bottom);
    
    CGContextRef ctx = UIGraphicsGetCurrentContext();
    
    NSDictionary *attrDictionary = @{NSFontAttributeName: self.font,
                                     NSForegroundColorAttributeName: self.textColor
                                    };
    NSAttributedString *attrString = [[NSAttributedString alloc] initWithString:self.text attributes:attrDictionary];
    
    CFAttributedStringRef drawStr = CFBridgingRetain(attrString);
    CTFramesetterRef setter = CTFramesetterCreateWithAttributedString(drawStr);
    CGPathRef path = CGPathCreateWithRect(insetRect, NULL);
    CTFrameRef frame = CTFramesetterCreateFrame(setter, CFRangeMake(0, CFAttributedStringGetLength(drawStr)), path, NULL);
    
    CGContextSaveGState(ctx);
    CGContextScaleCTM(ctx, 1, -1);
    CGContextTranslateCTM(ctx, 0, -CGRectGetHeight(insetRect));
    CTFrameDraw(frame, ctx);
    CGContextRestoreGState(ctx);
    
    CGPathRelease(path);
    CFRelease(frame);
    CFRelease(setter);
    CFRelease(drawStr);
}

- (BOOL)hasText{
    return self.text.length > 0;
}

- (void)insertText:(NSString *)text {
    if ([self.delegate respondsToSelector:@selector(editViewDidBeginEditing:)]){
        [self.delegate editViewDidBeginEditing:self];
    }
    
    if ([self.delegate respondsToSelector:@selector(editViewShouldReturn:inChange:)]){
        if ([self.delegate editViewShouldReturn:self inChange:text] == YES){
            return;
        }
    }
    
    if ([self.text isEqualToString:@"\n"]){
        [self resignFirstResponder];
        [self setNeedsDisplay];
        return;
    }
    
    self.text = [self.text stringByAppendingString:text];
    
    CGPoint cursorPoint = [self getLiveTextLeadingLocationIn:self.text];
    self.cursor.frame = CGRectMake(cursorPoint.x, cursorPoint.y, self.cursor.frame.size.width, self.cursor.frame.size.height);
    
    if ([self.delegate respondsToSelector:@selector(editViewDidChange:)]){
        [self.delegate editViewDidChange:self];
    }
    [self setNeedsDisplay];
    
    if ([self.delegate respondsToSelector:@selector(editViewDidEndEditing:)]){
        [self.delegate editViewDidEndEditing:self];
    }
}

- (void)deleteBackward {
    if (self.text.length > 0) {
        self.text = [self.text substringToIndex:[self.text length] -1];
    } else {
        self.text = @"";
    }
    
    CGPoint cursorPoint = [self getLiveTextLeadingLocationIn:self.text];
    self.cursor.frame = CGRectMake(cursorPoint.x, cursorPoint.y, self.cursor.frame.size.width, self.cursor.frame.size.height);
    
    [self setNeedsDisplay];
}

- (void)setPlaceholder:(NSString *)placeholder {
    self.placeholderLabel.text = placeholder;
}

- (UILabel *)placeholderLabel {
    if (!_placeholderLabel){
        _placeholderLabel = [[UILabel alloc] init];
        _placeholderLabel.textColor = [UIColor lightGrayColor];
        _placeholderLabel.frame = CGRectMake(0, 0, CGRectGetWidth(self.frame), 20);
        
    }
    return _placeholderLabel;
}

- (UIFont *)font {
    if (!_font){
        _font = [UIFont systemFontOfSize:16 weight:UIFontWeightLight];
    }
    return _font;
}

- (UIColor *)textColor {
    if (!_textColor){
        _textColor = [UIColor blackColor];
    }
    return _textColor;
}

- (UIView *)cursor {
    if (!_cursor){
        _cursor = [[UIView alloc] init];
        _cursor.layer.cornerRadius = 1;
        _cursor.backgroundColor = [[UIColor blueColor] colorWithAlphaComponent:0.4];
    }
    return _cursor;
}

- (BOOL)canBecomeFirstResponder {
    return YES;
}

- (CGPoint)getLiveTextLeadingLocationIn: (NSString *)text {
    const CGFloat MAX_SINGLE_W = CGRectGetWidth(self.frame) - self.textContainerInset.left - self.textContainerInset.right;
    const CGFloat FONT_H = ceil(self.font.lineHeight);
    
    CGFloat finalH = [self fixWidthGetHeight:text
                                     andFont:self.font
                                     andFixW:MAX_SINGLE_W] - FONT_H;
    CGFloat realW = [self fixHeightGetWidth:text
                                    andFont:self.font
                                    andFixH:FONT_H];
    
    CGFloat reminderW = reminder(realW, MAX_SINGLE_W);
    CGFloat finalW = realW > MAX_SINGLE_W ? (reminderW + 3.5) : realW;
    return CGPointMake(finalW, finalH);
}

- (CGFloat)fixWidthGetHeight: (NSString *) string andFont: (UIFont *)font andFixW: (CGFloat)w{
    return [string boundingRectWithSize:CGSizeMake(w, CGFLOAT_MAX)
                                options:NSStringDrawingUsesLineFragmentOrigin | NSStringDrawingUsesFontLeading
                             attributes:@{ NSFontAttributeName: font }
                                context:nil].size.height;
}

- (CGFloat)fixHeightGetWidth: (NSString *) string andFont: (UIFont *)font andFixH: (CGFloat)h{
    return [string boundingRectWithSize:CGSizeMake(CGFLOAT_MAX, h)
                                options:NSStringDrawingUsesLineFragmentOrigin | NSStringDrawingUsesFontLeading
                             attributes:@{ NSFontAttributeName: font }
                                context:nil].size.width;
}

int reminder(CGFloat a, CGFloat b){
    int c = a;
    int d = b;
    return c - (c / d) * d;
}

@end

ViewController中调用：

import UIKit

class ViewController: UIViewController, SGEditViewDelegate{
    

    lazy var editView: SGEditView = {
        let edit = SGEditView(frame: CGRect(x: 20, y: 200, width: 375 - 40, height: 100))
        edit.backgroundColor = .gray
        edit.placeholder = "Input accout."
        edit.textContainerInset = UIEdgeInsets(top: 0, left: 0, bottom: 5, right: 10)
        return edit
    }()
    

    override func viewDidLoad() {
        super.viewDidLoad()


        self.view.addSubview(editView)
        editView.delegate = self
    }
    
    func editViewDidBeginEditing(_ editView: SGEditView!) {
        print("------> editViewDidBeginEditing: \(editView.text)")
    }
    
    func editViewShouldReturn(_ editView: SGEditView!, inChange text: String!) -> Bool {
        if editView.text.contains("abc") {
            return true
        }
        return false
    }
    
    
    func editViewDidChange(_ editView: SGEditView!) {
        print("------> editViewDidChange: \(editView.text)")
    }
    
    func editViewDidEndEditing(_ editView: SGEditView!) {
        print("------> editViewDidEndEditing: \(editView.text)")
    }
    
}