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];
}
}