UIGestureRecognizer - BNR

　　继续上篇UITouch - BNR。该篇将实现线条选择、移动和删除操作。

　　UIGestureRecognizer有一系列子类，每一个子类都用于识别特定的手势。当识别出一个手势时，手势识别器会拦截视图的触摸事件。

　　使用UITapGestureRecognizer类，实现当用户连续点击屏幕两次时，全部线条都被清空。

修改BNRDrawView类的initWithFrame:方法如下：

 - (instancetype)initWithFrame:(CGRect)r {
     self = [super initWithFrame:r];
     if (self) {
         self.linesInProgress = [[NSMutableDictionary alloc] init];
         self.finishedLines = [[NSMutableArray alloc] init];
         self.backgroundColor = [UIColor grayColor];
         self.multipleTouchEnabled = YES;

         UITapGestureRecognizer *doubleTapRecognizer = [[UITapGestureRecognizer alloc]
                                                        initWithTarget:self
                                                        action:@selector(doubleTap:)];
         doubleTapRecognizer.numberOfTapsRequired = ;
         doubleTapRecognizer.delaysTouchesBegan = YES;　　//使第一次点击不产生红点         [self addGestureRecognizer:doubleTapRecognizer];
     }
     return self;
 }

实现连续两次点击的doubleTap:响应事件，如下：

 - (void)doubleTap:(UIGestureRecognizer *)gr {
     NSLog(@"Recognized Double Tap");
     [self.linesInProgress removeAllObjects];
     [self.finishedLines removeAllObjects];
     [self setNeedsDisplay];
 }

---

添加手势识别，允许用户删除一条选定的线条。修改BNRDrawView类的initWithFrame:方法如下：

 - (instancetype)initWithFrame:(CGRect)r {
     self = [super initWithFrame:r];
     if (self) {
         self.linesInProgress = [[NSMutableDictionary alloc] init];
         self.finishedLines = [[NSMutableArray alloc] init];
         self.backgroundColor = [UIColor grayColor];
         self.multipleTouchEnabled = YES;

         UITapGestureRecognizer *doubleTapRecognizer = [[UITapGestureRecognizer alloc]
                                                        initWithTarget:self
                                                        action:@selector(doubleTap:)];
         doubleTapRecognizer.numberOfTapsRequired = ;
         doubleTapRecognizer.delaysTouchesBegan = YES;
         [self addGestureRecognizer:doubleTapRecognizer];

         UITapGestureRecognizer *tapRecognizer = [[UITapGestureRecognizer alloc]
                                                  initWithTarget:self
                                                  action:@selector(tap:)];
         tapRecognizer.delaysTouchesBegan = YES;
         [tapRecognizer requireGestureRecognizerToFail:doubleTapRecognizer]; //区别点击与双击手势
         [self addGestureRecognizer:tapRecognizer];
     }
     return self;
 }

实现单击的tap:响应事件，如下：

 - (void)tap:(UIGestureRecognizer *)gr {
     NSLog(@"Recognized Tap");
 }

在BNRDrawView.m文件的类扩展中声明selectedLine属性，用来表示被用户选中的线条，如下：

@property (nonatomic, weak) BNRLine *selectedLine;

　　其中，finishedLines数组拥有对selectedLine的强引用。当selectedLine从finishedLines中被删除时，将变为nil。

　　修改BNRDrawView类中drawRect:方法，使selectedLine显示绿色，如下：

 - (void)drawRect:(CGRect)rect {
     [[UIColor blackColor] set];
     for (BNRLine *line in self.finishedLines) {
         [self strokeLike:line];
     }
     [[UIColor redColor] set];
     for (NSValue *key in self.linesInProgress) {
         [self strokeLike:self.linesInProgress[key]];
     }
     if(self.selectedLine) {
         [[UIColor greenColor] set];
         [self strokeLike:self.selectedLine];
     }
 }

获取接近点击处的线条：

 - (BNRLine *)lineAtPoint:(CGPoint)p {
     for(BNRLine *l in self.finishedLines) {
         CGPoint start = l.begin;
         CGPoint end = l.end;
         for (float t = 0.0; t <= 1.0; t += 0.05) {
             float x = start.x + t * (end.x - start.x);
             float y = start.y + t * (end.y - start.y);
             if (hypot(x - p.x, y - p.y) < 20.0) {
                 return l;
             }
         }
     }
     return nil;
 }

最后修改点击手势响应事件tap:方法如下：

 - (void)tap:(UIGestureRecognizer *)gr {
     NSLog(@"Recognized Tap");

     CGPoint point = [gr locationInView:self];
     self.selectedLine = [self lineAtPoint:point];
     [self setNeedsDisplay];
 }

---

　　接下来实现，当用户已经选中一条线条之后，将显示一个菜单提供对该线条的删除操作。

修改tap:方法如下：

 - (void)tap:(UIGestureRecognizer *)gr {
     NSLog(@"Recognized Tap");
     CGPoint point = [gr locationInView:self];
     self.selectedLine = [self lineAtPoint:point];

     if(self.selectedLine) {
         //使该视图成为menu item响应方法的目标
         [self becomeFirstResponder];
         UIMenuController *menu = [UIMenuController sharedMenuController];
         //创建一个新的删除UIMenuItem
         UIMenuItem *deleteItem = [[UIMenuItem alloc] initWithTitle:@"Delete" action:@selector(deleteLine:)];
         menu.menuItems = @[deleteItem];
         //设置menu的显示位置
         [menu setTargetRect:CGRectMake(point.x, point.y, , ) inView:self];
         [menu setMenuVisible:YES animated:YES];
     } else {
         [[UIMenuController sharedMenuController] setMenuVisible:NO animated:YES];
     }

     [self setNeedsDisplay];
 }

　　当自定义的视图类需要成为第一响应者时，必须重载canBecomeFirstResponder方法，在BNRDrawView.m中添加如下方法：

 - (BOOL)canBecomeFirstResponder {
     return YES;
 }

　　如果menu items的响应方法没有实现，该menu就不会显示。实现deleteLine:方法如下：

 - (void)deleteLine:(id)sender {
     [self.finishedLines removeObject:self.selectedLine];
     [self setNeedsDisplay];
 }

运行程序，效果如下：

---

　　接下来，实现如下功能，当用户长按住一条线时，该线将被选中，用户能够用手指拖动该线条。修改initWithFrame:方法如下：

 - (instancetype)initWithFrame:(CGRect)r {
     self = [super initWithFrame:r];
     if (self) {
         self.linesInProgress = [[NSMutableDictionary alloc] init];
         self.finishedLines = [[NSMutableArray alloc] init];
         self.backgroundColor = [UIColor grayColor];
         self.multipleTouchEnabled = YES;

         UITapGestureRecognizer *doubleTapRecognizer = [[UITapGestureRecognizer alloc]
                                                        initWithTarget:self
                                                        action:@selector(doubleTap:)];
         doubleTapRecognizer.numberOfTapsRequired = ;
         doubleTapRecognizer.delaysTouchesBegan = YES;
         [self addGestureRecognizer:doubleTapRecognizer];

         UITapGestureRecognizer *tapRecognizer = [[UITapGestureRecognizer alloc]
                                                  initWithTarget:self
                                                  action:@selector(tap:)];
         tapRecognizer.delaysTouchesBegan = YES;
         [tapRecognizer requireGestureRecognizerToFail:doubleTapRecognizer]; //区别点击与双击手势
         [self addGestureRecognizer:tapRecognizer];

         UILongPressGestureRecognizer *pressRecognizer = [[UILongPressGestureRecognizer alloc]
                                                          initWithTarget:self
                                                          action:@selector(longPress:)];
         [self addGestureRecognizer:pressRecognizer];
     }
     return self;
 }

　　手势识别器处理长按时，其state属性会经历三种变化，其为 UIGestureRecognizerStatePossible  UIGestureRecognizerStateBegan  UIGestureRecognizerStateEnded 。

实现长按的响应方法longPress:如下：

 - (void)longPress:(UIGestureRecognizer *)gr {
     if (gr.state == UIGestureRecognizerStateBegan) {
         CGPoint point = [gr locationInView:self];
         self.selectedLine = [self lineAtPoint:point];
         if (self.selectedLine) {
             [self.linesInProgress removeAllObjects];
         }
     } else if (gr.state == UIGestureRecognizerStateEnded) {
             self.selectedLine = nil;
     }
     [self setNeedsDisplay];
 }

---

　让BNRDrawView遵守UIGestureRecognizerDelegate协议，并添加一个UIPanGestureRecognizer属性，如下：

 @interface BNRDrawView () <UIGestureRecognizerDelegate>

 @property (nonatomic, strong) UIPanGestureRecognizer *moveRecognizer;
 @property (nonatomic, strong) NSMutableDictionary *linesInProgress;
 @property (nonatomic, strong) NSMutableArray *finishedLines;
 @property (nonatomic, weak) BNRLine *selectedLine;

 @end

修改initWithFrame:方法。此处cancelsTouchesInView属性默认为YES，意味着手势识别器将吞没任何它识别出的手势，这样的话，视图将没有机会对UIRespnder方法做出响应。将其设置为NO，这样，手势识别器能识别的触摸事件也会被UIResponder识别。代码如下：

 - (instancetype)initWithFrame:(CGRect)r {
     self = [super initWithFrame:r];
     if (self) {
         self.linesInProgress = [[NSMutableDictionary alloc] init];
         self.finishedLines = [[NSMutableArray alloc] init];
         self.backgroundColor = [UIColor grayColor];
         self.multipleTouchEnabled = YES;

         UITapGestureRecognizer *doubleTapRecognizer = [[UITapGestureRecognizer alloc]
                                                        initWithTarget:self
                                                        action:@selector(doubleTap:)];
         doubleTapRecognizer.numberOfTapsRequired = ;
         doubleTapRecognizer.delaysTouchesBegan = YES;
         [self addGestureRecognizer:doubleTapRecognizer];

         UITapGestureRecognizer *tapRecognizer = [[UITapGestureRecognizer alloc]
                                                  initWithTarget:self
                                                  action:@selector(tap:)];
         tapRecognizer.delaysTouchesBegan = YES;
         [tapRecognizer requireGestureRecognizerToFail:doubleTapRecognizer]; //区别点击与双击手势
         [self addGestureRecognizer:tapRecognizer];

         UILongPressGestureRecognizer *pressRecognizer = [[UILongPressGestureRecognizer alloc]
                                                          initWithTarget:self
                                                          action:@selector(longPress:)];
         [self addGestureRecognizer:pressRecognizer];

         self.moveRecognizer = [[UIPanGestureRecognizer alloc] initWithTarget:self action:@selector(moveLine:)];
         self.moveRecognizer.delegate = self;
         self.moveRecognizer.cancelsTouchesInView = NO;
         [self addGestureRecognizer:self.moveRecognizer];
     }
     return self;
 }

实现UIGestureRecognizerDelegate协议的gestureRecognizer:shouldRecognizeSimultaneouslyWithGestureRecognizer:方法，如果该方法返回YES，手势识别器将与其它的识别器分享该触摸事件。如下：

 - (BOOL)gestureRecognizer:(UIGestureRecognizer *)gestureRecognizer shouldRecognizeSimultaneouslyWithGestureRecognizer:(UIGestureRecognizer *)otherGestureRecognizer {
     if (gestureRecognizer == self.moveRecognizer) {
         return YES;
     }
     return NO;
 }

实现移动手势的响应事件moveLine:，如下：

 - (void)moveLine:(UIPanGestureRecognizer *)gr {
     if (!self.selectedLine) {
         return;
     }
     if (gr.state == UIGestureRecognizerStateChanged) {
         CGPoint translation = [gr translationInView:self];
         CGPoint begin = self.selectedLine.begin;
         CGPoint end = self.selectedLine.end;
         begin.x += translation.x;
         begin.y += translation.y;
         end.x += translation.x;
         end.y += translation.y;
         self.selectedLine.begin = begin;
         self.selectedLine.end = end;
         [self setNeedsDisplay];
         [gr setTranslation:CGPointZero inView:self];
     }
 }

程序代码链接：http://pan.baidu.com/s/1o6Dz5xg