iOS：练习题中如何用技术去实现一个连线题

一、介绍

本人做的app涉及的是教育行业，所以关于练习题的开发肯定是家常便饭。例如，选择题、填空题、连线题、判断题等，每一种题型都需要技术去实现，没啥多大难度，这里呢，就给出实现连线题的核心代码吧。过了年后，好久没写笔记了，今天就简单开始吧~~~

 

二、思想

采用上下文在画图的方法，首先确定起点和终点的坐标，然后通过两点画一条直线。

 

三、代码

(1)常量定义

lianXianHeader.h

//
//  LianXianHeader.h
//  LianxianDemo
//
//  Created by 夏远全 on 2018/2/9.
//  Copyright © 2018年 beijing. All rights reserved.
//

#ifndef LianXianHeader_h
#define LianXianHeader_hstatic CGFloat const BWidth   = 60;  //按钮的宽度
static CGFloat const BHeight  = 40;  //按钮的高度
static CGFloat const margin   = 40;  //按钮与屏幕的左边距、右边距
static CGFloat const Lpadding = 20;  //左边按钮上下间距
static CGFloat const Rpadding = 40;  //右边按钮上下间距static NSString* const kBeginPositionNotification = @"kBeginPositionNotification";
static NSString* const kEndPositionNotification   = @"kEndPositionNotification";
static NSString* const kClearAllLineNotification  = @"kClearAllLineNotification";
static NSString* const kFreshDrawLineNotification = @"kFreshDrawLineNotification";#endif /* LianXianHeader_h */
View Code

 

(2)连线模型

lianXianModel.h

//
//  LianXianModel.h
//  LianxianDemo
//
//  Created by 夏远全 on 2018/2/8.
//  Copyright © 2018年 beijing. All rights reserved.
//

#import <Foundation/Foundation.h>
#import <UIKit/UIKit.h>@interface LianXianModel : NSObject
@property (nonatomic, strong) NSArray  *questions;
@property (nonatomic, strong) NSArray  *options;
@property (nonatomic, strong) NSArray  *relationships;
@end
View Code

lianXianModel.m

//
//  LianXianModel.m
//  LianxianDemo
//
//  Created by 夏远全 on 2018/2/8.
//  Copyright © 2018年 beijing. All rights reserved.
//

#import "LianXianModel.h"@implementation LianXianModel@end
View Code

 

(3)绘制连线

lianXianDrawView.h

//
//  LianxianDrawView.h
//  Ubbsz
//
//  Created by 夏远全 on 2018/2/9.
//  Copyright © 2018年 beijing. All rights reserved.
//
//

#import <UIKit/UIKit.h>@interface LianxianDrawView : UIView@end
View Code

lianXianDrawView.m

//
//  LianxianDrawView.m
//  Ubbsz
//
//  Created by 夏远全 on 2018/2/9.
//  Copyright © 2018年 beijing. All rights reserved.
//
#import "LianxianDrawView.h"
#import "LianXianHeader.h"@interface LianxianDrawView()
{NSMutableArray *pointArray; //存储当前的一对坐标，起始点和终止点NSMutableArray *lineArray;  //存储全部的连线，每一条连线就是一对坐标NSString       *startPointString; //当前起点NSString       *endPointString;   //当前起点
    CGFloat        lineWidth;
}@end@implementation LianxianDrawView//对进行重写，以便在视图初始化的时候创建并设置自定义的Context
- (id)initWithFrame:(CGRect)frame
{if (self = [super initWithFrame:frame]) {[self setupDefaultValue];[self regesterNotification];}return self;
}//初始值
- (void)setupDefaultValue{pointArray=[[NSMutableArray alloc]init];lineArray=[[NSMutableArray alloc]init];lineWidth = 2.0f;self.backgroundColor = [UIColor colorWithRed:238/255.0 green:243/255.0  blue:248/255.0  alpha:1];
}//注册通知
- (void)regesterNotification{[[NSNotificationCenter defaultCenter] addObserver:self selector:@selector(toucheBegin:) name:kBeginPositionNotification object:nil];[[NSNotificationCenter defaultCenter] addObserver:self selector:@selector(toucheEnd:) name:kEndPositionNotification object:nil];[[NSNotificationCenter defaultCenter] addObserver:self selector:@selector(clearLine:) name:kClearAllLineNotification object:nil];[[NSNotificationCenter defaultCenter] addObserver:self selector:@selector(freshNeedsDisplay:) name:kFreshDrawLineNotification object:nil];
}//对drawRect进行重写
- (void)drawRect:(CGRect)rect
{//获取当前上下文，CGContextRef context=UIGraphicsGetCurrentContext();CGContextBeginPath(context);CGContextSetLineWidth(context, lineWidth);//线条拐角样式，设置为平滑
    CGContextSetLineJoin(context,kCGLineJoinRound);//线条开始样式，设置为平滑
    CGContextSetLineCap(context, kCGLineCapRound);//查看lineArray数组里是否有线条，有就将之前画的重绘，没有只画当前线条if ([lineArray count] > 0) {for (int i=0; i < [lineArray count]; i++) {NSArray * array=[NSArray arrayWithArray:[lineArray objectAtIndex:i]];if ([array count] > 0 && [array count]%2 == 0) {CGContextBeginPath(context);CGPoint myStartPoint = CGPointFromString(array.firstObject);CGContextMoveToPoint(context, myStartPoint.x, myStartPoint.y);CGPoint myEndPoint = CGPointFromString(array.lastObject);CGContextAddLineToPoint(context, myEndPoint.x,myEndPoint.y);CGContextSetStrokeColorWithColor(context,[[UIColor grayColor] CGColor]);CGContextSetLineWidth(context, lineWidth);CGContextStrokePath(context);}}}
}//接收起点按钮点击通知事件
- (void)toucheBegin:(NSNotification *)notification{CGRect beginFrame = [notification.object CGRectValue];CGPoint startPoint = CGPointMake(CGRectGetMaxX(beginFrame), CGRectGetMidY(beginFrame));startPointString = NSStringFromCGPoint(startPoint);if (pointArray.count==0) {[pointArray addObject:startPointString];}else{[pointArray replaceObjectAtIndex:0 withObject:startPointString];}
}//接收终点按钮点击通知事件
- (void)toucheEnd:(NSNotification *)notification{CGRect endFrame = [notification.object CGRectValue];CGPoint endPoint = CGPointMake(CGRectGetMinX(endFrame), CGRectGetMidY(endFrame));endPointString = NSStringFromCGPoint(endPoint);if (pointArray.count==2) {[pointArray replaceObjectAtIndex:1 withObject:endPointString];}else{[pointArray addObject:endPointString];}[self clearSomeHistoryLineView];[self addLA];[self setNeedsDisplay];
}//接收清除按钮点击通知事件
- (void)clearLine:(NSNotification *)notification{[self clearAllLineView];
}//接收重新绘制通知事件
- (void)freshNeedsDisplay:(NSNotification *)notification{NSArray *relationslineArray = notification.object;lineArray = [NSMutableArray arrayWithArray:relationslineArray];[self setNeedsDisplay];
}//添加连线
-(void)addLA{NSArray *array = [NSArray arrayWithArray:pointArray];[lineArray addObject:array];[pointArray removeAllObjects];
}//清除所有的连线
- (void)clearAllLineView
{[pointArray removeAllObjects];[lineArray removeAllObjects];[self setNeedsDisplay];
}//移除历史交叉重复的连线
- (void)clearSomeHistoryLineView{NSMutableArray *arrayM = [NSMutableArray array];for (int i=0; i < [lineArray count]; i++) {NSArray *array = [NSArray arrayWithArray:[lineArray objectAtIndex:i]];if ([array count] > 0) {NSString *hisBePointString = array.firstObject;NSString *hisEnPointString = array.lastObject;if ([startPointString isEqualToString:hisBePointString] || [endPointString isEqualToString:hisEnPointString]) {[arrayM addObject:array];}}}[lineArray removeObjectsInArray:arrayM];
}//移除通知
-(void)dealloc{[[NSNotificationCenter defaultCenter] removeObserver:self];
}@end
View Code

 

(4)计算尺寸

LianXianFrameUitity.h

//
//  LianXianSizeUitity.h
//  LianxianDemo
//
//  Created by 夏远全 on 2018/2/9.
//  Copyright © 2018年 beijing. All rights reserved.
//

#import <Foundation/Foundation.h>
#import "LianXianModel.h"@interface LianXianFrameUitity : NSObject+ (CGRect)calculateSizeWithModel:(LianXianModel *)lianxianModel;@end
View Code

LianXianFrameUitity.m 

//
//  LianXianSizeUitity.m
//  LianxianDemo
//
//  Created by 夏远全 on 2018/2/9.
//  Copyright © 2018年 beijing. All rights reserved.
//

#import "LianXianFrameUitity.h"
#import "LianXianHeader.h"@implementation LianXianFrameUitity+ (CGRect)calculateSizeWithModel:(LianXianModel *)lianxianModel{NSUInteger questionsCount = lianxianModel.questions.count;NSUInteger optionsCount = lianxianModel.options.count;CGFloat LHeight = questionsCount * (BHeight+Lpadding) + Lpadding;CGFloat RHeight = optionsCount * (BHeight+Rpadding) + Rpadding;CGFloat kWidth  = [UIScreen mainScreen].bounds.size.width; //默认宽度为屏幕的宽return CGRectMake(0, 0, kWidth, MAX(LHeight, RHeight));
}@end
View Code

 

(5)创建组件

LianXianComponentsView.h

//
//  LianXianComponentsView.h
//  LianxianDemo
//
//  Created by 夏远全 on 2018/2/6.
//  Copyright © 2018年 beijing. All rights reserved.
//

#import <UIKit/UIKit.h>
#import "LianXianModel.h"@interface LianXianComponentsView : UIView
@property (nonatomic, strong) LianXianModel *lianxianModel;
@end
View Code

LianXianComponentsView.m

//
//  LianXianComponentsView.m
//  LianxianDemo
//
//  Created by 夏远全 on 2018/2/6.
//  Copyright © 2018年 beijing. All rights reserved.
//

#import "LianXianComponentsView.h"
#import "LianxianDrawView.h"
#import "LianXianHeader.h"@interface LianXianComponentsView() {NSMutableArray *_leftBtns;NSMutableArray *_rightBtns;UIButton       *currentLeftBtn;CGFloat        borderWith;
}@end@implementation LianXianComponentsView//对进行重写，以便在视图初始化的时候创建并设置自定义的Context
- (id)initWithFrame:(CGRect)frame
{if (self = [super initWithFrame:frame]) {[self setupDefalutValue];}return self;
}//设置默认值
- (void)setupDefalutValue{self.backgroundColor = [UIColor clearColor];borderWith = 2.5;[[NSNotificationCenter defaultCenter] addObserver:self selector:@selector(restStatus:) name:kClearAllLineNotification object:nil];
}//接收模型
-(void)setLianxianModel:(LianXianModel *)lianxianModel{_lianxianModel = lianxianModel;[self setupLianXianUnit];if (lianxianModel && lianxianModel.relationships.count>0) {[self showLianXianResult];}else{[self listClickLeftButton];}
}//绘制连线选项
- (void)setupLianXianUnit{_leftBtns  = [[NSMutableArray array] init];_rightBtns = [[NSMutableArray array] init];CGFloat kWidth   = self.frame.size.width;CGFloat kHeight  = self.frame.size.height;CGFloat LY = (kHeight-(BHeight+Lpadding)*(self.lianxianModel.questions.count-1) - BHeight)/2;CGFloat RY = (kHeight-(BHeight+Rpadding)*(self.lianxianModel.options.count-1) - BHeight)/2;for (NSInteger i =0; i < self.lianxianModel.questions.count; i++) {UIButton *btn = [self createButtonWithFrame:CGRectMake(margin, LY+(BHeight+Lpadding)*i, BWidth, BHeight) title:[NSString stringWithFormat:@"%@",self.lianxianModel.questions[i]] tag:i];[self addSubview:btn];[_leftBtns addObject:btn];}for (NSInteger i =0; i< self.lianxianModel.options.count; i++) {UIButton *btn = [self createButtonWithFrame:CGRectMake(kWidth-margin-BWidth, RY+(BHeight+Rpadding)*i, BWidth, BHeight) title:[NSString stringWithFormat:@"%@",self.lianxianModel.options[i]] tag:i];[self addSubview:btn];[_rightBtns addObject:btn];}
}-(UIButton *)createButtonWithFrame:(CGRect)frame title:(NSString *)title tag:(NSInteger)tag{UIButton *btn = [UIButton buttonWithType:UIButtonTypeCustom];btn.frame = frame;btn.layer.cornerRadius = 5.0;btn.layer.borderColor = [UIColor lightGrayColor].CGColor;btn.layer.borderWidth = borderWith;btn.layer.masksToBounds = YES;btn.tag = tag;[btn setBackgroundImage:[self imageWithColor:[UIColor whiteColor]] forState:UIControlStateNormal];[btn setBackgroundImage:[self imageWithColor:[UIColor colorWithRed:138/255.0 green:193/255.0 blue:211/255.0 alpha:1]] forState:UIControlStateHighlighted];[btn setBackgroundImage:[self imageWithColor:[UIColor colorWithRed:138/255.0 green:193/255.0 blue:211/255.0 alpha:1]] forState:UIControlStateSelected];[btn addTarget:self action:@selector(tapBtn:) forControlEvents:UIControlEventTouchUpInside];[btn setTitle:title forState:UIControlStateNormal];[btn setTitleColor:[UIColor blackColor] forState:UIControlStateNormal];return btn;
}- (UIImage *)imageWithColor:(UIColor *)color
{CGFloat imageW = 20;CGFloat imageH = 20;UIGraphicsBeginImageContextWithOptions(CGSizeMake(imageW, imageH), NO, 0.0);[color set];UIRectFill(CGRectMake(0, 0, imageW, imageH));UIImage *image = UIGraphicsGetImageFromCurrentImageContext();UIGraphicsEndImageContext();return image;
}-(void)tapBtn:(UIButton *)btn{//判断左边按钮是否处于选择状态，只有首先左边处于此状态下，右边的按钮点击才能进行连线操作（当前仅支持单向连线）if ([_rightBtns containsObject:btn]) {BOOL isLeftBtnSelected = NO;for (UIButton *leftBtn in _leftBtns) {if (leftBtn.selected) {isLeftBtnSelected = YES;break;}}if (!isLeftBtnSelected) {return;}}if ([_leftBtns containsObject:btn]) {//设置连线起点currentLeftBtn.selected = NO;currentLeftBtn.layer.borderColor = [UIColor lightGrayColor].CGColor;btn.selected = YES;currentLeftBtn = btn;currentLeftBtn.layer.borderColor = [UIColor colorWithRed:32/255.0 green:199/255.0 blue:251/255.0 alpha:1].CGColor;//设置终点按钮可以选中状态for (UIButton *rightBtn in _rightBtns) {rightBtn.layer.borderColor = [UIColor colorWithRed:32/255.0 green:199/255.0 blue:251/255.0 alpha:1].CGColor;}//发送起点通知[[NSNotificationCenter defaultCenter] postNotificationName:kBeginPositionNotification object:[NSValue valueWithCGRect:btn.frame]];}if ([_rightBtns containsObject:btn]) {for (UIButton *leftBtn in _leftBtns) {if (leftBtn.selected) {//发送终点通知[[NSNotificationCenter defaultCenter] postNotificationName:kEndPositionNotification object:[NSValue valueWithCGRect:btn.frame]];//自动设置起始选择按钮
                [self listClickLeftButton];break;}}}
}//自动设置起始选择按钮
- (void)listClickLeftButton{if (!currentLeftBtn) {[self tapBtn:_leftBtns[0]];return;}NSUInteger tag = currentLeftBtn.tag;if (tag < _leftBtns.count-1) {  //自动下移[self tapBtn:_leftBtns[tag+1]];}else{[self tapBtn:_leftBtns[0]]; //重新开始
    }
}//绘制默认已经连线的选项，此处仅仅做成绩预览使用，不能再编辑
- (void)showLianXianResult{for (UIButton *leftBtn in _leftBtns) {leftBtn.layer.borderColor = [UIColor lightGrayColor].CGColor;leftBtn.selected = leftBtn.userInteractionEnabled = NO;}for (UIButton *rightBtn in _rightBtns) {rightBtn.layer.borderColor = [UIColor lightGrayColor].CGColor;rightBtn.selected = rightBtn.userInteractionEnabled = NO;}if (self.lianxianModel.relationships.count == 0) {return;}NSMutableArray *relationslineArray = [NSMutableArray array];for (NSString *result in self.lianxianModel.relationships) {NSString *question = [[result componentsSeparatedByString:@"-"] firstObject];NSString *option   = [[result componentsSeparatedByString:@"-"] lastObject];NSMutableArray *pointArray = [NSMutableArray array];for (UIButton *leftBtn in _leftBtns) {if ([leftBtn.currentTitle isEqualToString:question]) {CGPoint startPoint = CGPointMake(CGRectGetMaxX(leftBtn.frame), CGRectGetMidY(leftBtn.frame));NSString *startPointString = NSStringFromCGPoint(startPoint);[pointArray addObject:startPointString];break;}}for (UIButton *rightBtn in _rightBtns) {if ([rightBtn.currentTitle isEqualToString:option]) {CGPoint endPoint = CGPointMake(CGRectGetMinX(rightBtn.frame), CGRectGetMidY(rightBtn.frame));NSString *endPointString = NSStringFromCGPoint(endPoint);[pointArray addObject:endPointString];break;}}[relationslineArray addObject:pointArray];}if (relationslineArray.count > 0) {[[NSNotificationCenter defaultCenter] postNotificationName:kFreshDrawLineNotification object:relationslineArray];}
}//重置初始状态
- (void)restStatus:(NSNotification *)notification{for (UIButton *leftBtn in _leftBtns) {leftBtn.selected = NO;leftBtn.layer.borderColor = [UIColor lightGrayColor].CGColor;[self tapBtn:_leftBtns[0]]; //重新开始
    }
}@end
View Code

 

(6)连线容器

LianXianContainerView.h

//
//  LianXianContainerView.h
//  LianxianDemo
//
//  Created by 夏远全 on 2018/2/8.
//  Copyright © 2018年 beijing. All rights reserved.
//

#import <UIKit/UIKit.h>
#import "LianXianComponentsView.h"
#import "LianxianDrawView.h"@interface LianXianContainerView : UIView
@property (nonatomic, strong) LianXianComponentsView *componentsView;
@property (nonatomic, strong) LianxianDrawView *lianXianView;
@end
View Code

LianXianContainerView.m

//
//  LianXianContainerView.m
//  LianxianDemo
//
//  Created by 夏远全 on 2018/2/8.
//  Copyright © 2018年 beijing. All rights reserved.
//

#import "LianXianContainerView.h"
#import "LianXianComponentsView.h"
#import "LianxianDrawView.h"
#import "LianXianModel.h"@implementation LianXianContainerView- (id)initWithFrame:(CGRect)frame
{if (self = [super initWithFrame:frame]) {[self setup];}return self;
}- (void)setup{self.lianXianView = [[LianxianDrawView alloc]initWithFrame:self.bounds];self.componentsView = [[LianXianComponentsView alloc] initWithFrame:self.bounds];[self addSubview:self.lianXianView];[self addSubview:self.componentsView];
}@end
View Code

 

(7)显示连线

//
//  ViewController.m
//  LianxianDemo
//
//  Created by tianjing on 15/3/31.
//  Copyright © 2015年 tianjing. All rights reserved.
//

#import "ViewController.h"#import "LianXianContainerView.h"
#import "LianXianFrameUitity.h"
#import "LianXianModel.h"
#import "LianXianHeader.h"@interface ViewController ()@end@implementation ViewController- (void)viewDidLoad {[super viewDidLoad];UIButton *clearBtn = [[UIButton alloc] initWithFrame:CGRectMake(50, 50, 100, 40)];clearBtn.backgroundColor = [UIColor greenColor];[clearBtn setTitle:@"重置" forState:UIControlStateNormal];[clearBtn setTitleColor:[UIColor redColor] forState:UIControlStateNormal];[clearBtn addTarget:self action:@selector(clear:) forControlEvents:UIControlEventTouchUpInside];//创建模型LianXianModel *lianxianModel = [[LianXianModel alloc] init];lianxianModel.questions = @[@"天",@"好",@"人"]; /// 左边选项lianxianModel.options = @[@"夏",@"世",@"锋"];   /// 右边选项//lianxianModel.relationships = @[@"天-世",@"好-夏",@"人-锋"]; /// 连线关系，如果不为空，就只显示，不能编辑//clearBtn.hidden = (lianxianModel.relationships.count>0);//连线视图CGRect frame = [LianXianFrameUitity calculateSizeWithModel:lianxianModel];LianXianContainerView *containerView = [[LianXianContainerView alloc] initWithFrame:frame];containerView.center = self.view.center;containerView.componentsView.lianxianModel = lianxianModel;[self.view addSubview:containerView];[self.view addSubview:clearBtn];
}- (void)clear:(UIButton *)sender{[[NSNotificationCenter defaultCenter] postNotificationName:kClearAllLineNotification object:nil];
}@end
View Code

 

四、效果

提示：

左边按钮每次只有一个处于可连状态，而且每一次连接完会循环自动下移。

右边所有按钮始终处于可连状态。

同一个按钮再一次连接新的连线后，之前旧的跟其相关的连线都会被取消。 

 

  

 

五、采坑

如果练习题的界面是放在cell中的，因为复用的问题，在发送起点和终点的通知时，要对通知做唯一标识处理。

如果不这么做，可能会出现的bug是：上一道做过的连线题的连线会出现在下一道还没有做过的连线题上。

 

转载于:https://www.cnblogs.com/XYQ-208910/p/8532379.html

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今天看别人的代码&#xff0c;突然发现之前理解的sql的with as的用法有新的理解。 之前理解的with as只是想着做单表的union all 操作时才使用&#xff0c;今天发现在可以使用逗号做分割&#xff0c;做缓存不同的表数据。 下面的例子如下&#xff1a; WITH t1 AS (SELECT file_…
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javascript --- 从数组中,找出比给定元素大一丁点的元素

javascript --- 从数组中,找出比给定元素大一丁点的元素

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22 React高阶组件

22 React高阶组件

搭建服务端 yarn add express yarn add nodemon 在server目录下 npm init -y // 增加dev脚本"scripts": {"dev": "nodemon ./index.js"},引入 git HOC High Order Component 高阶组件&#xff0c;是组件的抽象HOC不是React提供的API&#xf…
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AngularJS：表达式

AngularJS：表达式

ylbtech-AngularJS&#xff1a;表达式1.返回顶部 1、AngularJS 表达式 AngularJS 使用 表达式 把数据绑定到 HTML。 AngularJS 表达式 AngularJS 表达式写在双大括号内&#xff1a;{{ expression }}。 AngularJS 表达式把数据绑定到 HTML&#xff0c;这与 ng-bind 指令有异曲同…
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省选模拟赛记录(越往下越新哦~~~)

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LOG 模拟赛第一次见尼玛这么给数据范围的……开考有点困,迷迷糊糊看完了三道题,真的是像老吕说的那样,一道都不会……思考T1,感觉有点感觉,但是太困了,就先码了暴力,发现打表可以50分,于是就大力打了一波表……转身T3,码出25分的O(n^2)算法,然后不会了……去了T2,码出35分的O(n…
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flutter --- 使用dio包

flutter --- 使用dio包

打开pubspec.yaml找到dependencies在最下面添加 dio: ^1.0.9ctrl s 之后,会自动下载依赖 使用: // get请求 import package:dio/dio.dart; Dio dio new Dio(); var response await dio.get("/test", data:{"id":12, "name":"marron&qu…
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24 React.createRef()用法细节分析

24 React.createRef()用法细节分析

通过React.createRef → ref对象通过元素的ref属性可以附加到React元素上一般通过构造器中给this的属性赋值一个ref&#xff0c;方便整个组件使用ref只要传递到react元素中&#xff0c;就可以利用ref的current属性访问到该真实DOM节点ref在componentDidMount和componentDidUpda…
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dart --- 环境配置

dart --- 环境配置

1.进入官网下载SDK http://www.gekorm.com/dart-windows/ 2.运行下载的EXE文件.下一步下一步… 3.打开小黑框,输入: dart --version VSCode关于Dart的插件: DartCode Runner 插件安装好后,需重启VSCode. 新建 index.dart,输入以下代码 main () {print("Hello Dart…
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25 Refs转发机制与在高阶组件中的使用

25 Refs转发机制与在高阶组件中的使用

将子节点的ref暴露给父节点 16.3以上 Refs转发&#xff0c;将ref自动通过组件传递给子组件 1. 在父组件创建ref对象 2. 给子组件赋值ref 3. 通过React.forward向子组件转发ref属性 4. 父组件的ref对象指向子组件dom 5. ref参数只有在 React.forwardRef 组件内定义时可接受con…
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26 JSX深度剖析与使用技巧

26 JSX深度剖析与使用技巧

React对JSX的处理 React.createElement有三个参数&#xff1a;标签类型&#xff0c;属性集合&#xff0c;子元素 JSX其实是React.createElement函数调用的语法糖 JSX → 编译 → React.createElement调用形式 class App extends React.Component {render() {return (<div cl…
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javascript --- 数组实用小技巧

javascript --- 数组实用小技巧

一个数组:[a,b,c,d,e],希望满足以下2个条件: 1.当索引在第0个位置的时候,数组为[b,c,d,e],在第1个位置的时候,数组为[a,c,d,e] … 2.若索引i 和 索引 j 的值相等,则只执行1次. 效果如下: nums [1,2,3,4] nums [1,1,1,2,2,3,4] 实现如下: let nums [1,1,1,2,2,3,4]; let le…
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Http的持久连接和管线化

Http的持久连接和管线化

【要点】 1. 什么是持久连接&#xff1f; 2. 什么是管线化&#xff1f; 【总结】 1.什么是持久连接&#xff1f; (keep alive模式) HTTP1.1规定了默认保持长连接&#xff08;HTTP persistent connection &#xff0c;也有翻译为持久连接&#xff09;;数据传输完成了保持TCP连接…
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dart --- 简单的闭包

dart --- 简单的闭包

首先得明白下面2点: 全局变量的特点:常驻内存,污染全局变量局部变量的特点:会被垃圾回收机制回收,不会污染作用域… // 闭包.dart void main(){myClosure(){var a 0; // a是一个局部变量.函数执行完毕后将被清理return (){a;print(a);};}var fn myClosure();fn();fn();fn()…
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