<原>第五章－CoreText

<原>第五章－CoreText－学习笔记1

转载请著名作者以及出处

首先说一下实现的原理，首先当手指开始触摸屏幕以及滑动的时候，效果与画矩形框是一样的因此此时的代码也机会没有区别，

当手指松开后在当前的矩形框处创建一个临时的textView ，并且背景变为灰色，textView 编辑结束，在textView的完成委托方法中去掉灰色的背景去掉临时的textView 在相同的位置上利用coreText 显示出刚才编辑的内容

首先手指触摸会调用到

TextTool.m

- (void)touchesBegan:(NSSet *)touches withEvent:(UIEvent *)event {
  UIView *touchedView = [delegate viewForUseWithTool:self];
 //注意下面这句代码
  [touchedView endEditing:YES];
  // we only track one touch at a time for this tool.
  UITouch *touch = [[event allTouches] anyObject];
  // remember the touch, and its original start point, for future
  [trackingTouches addObject:touch];
  CGPoint location = [touch locationInView:touchedView];
  [startPoints addObject:[NSValue valueWithCGPoint:location]];
}

代码除了注释的那一句基本上与前面的矩形是相同的纪录下来 UITouch 的实例以及开始的点

而注释那一句得到的touchedView 就是dudelView 如果此处设置为yes 在textView 成为第一响应弹出键盘后，我们可以直接触摸view 来取消TextView的第一响应状态

随着手指移动不断调用到 touchMoved 但是与前面矩形的实现一样这里的touchMoved方法为空画出临时矩形的实现代码在

drawTemporary 方法中

TextTool.m

- (void)drawTemporary {
  if (self.completedPath) {
    [delegate.strokeColor setStroke];
    [self.completedPath stroke];
  } else {
    UIView *touchedView = [delegate viewForUseWithTool:self];
    for (int i = 0; i<[trackingTouches count]; i++) {
      UITouch *touch = [trackingTouches objectAtIndex:i];
      CGPoint startPoint = [[startPoints objectAtIndex:i] CGPointValue];
      CGPoint endPoint = [touch locationInView:touchedView];
      CGRect rect = CGRectMake(startPoint.x, startPoint.y, endPoint.x - startPoint.x, endPoint.y - startPoint.y);
      UIBezierPath *path = [UIBezierPath bezierPathWithRect:rect];
      [delegate.strokeColor setStroke];
      [path stroke];
    }
  }
}

completedPath是一个UIBezierPath 的实例，在touchEnded方法中将最终矩形的路径设置到其中，所以在手指抬起来以前都只会进入到else分支，根据起点与当前手指触摸的点描出一个矩形来

当手指抬起来后进入touchEnded方法，而主要的实现代码就在这里面

TextTool.m

- (void)touchesEnded:(NSSet *)touches withEvent:(UIEvent *)event {
  UIView *touchedView = [delegate viewForUseWithTool:self];
  for (UITouch *touch in [event allTouches]) {
    // make a rect from the start point to the current point
    NSUInteger touchIndex = [trackingTouches indexOfObject:touch];
    // only if we actually remember the start of this touch...
    if (touchIndex != NSNotFound) {
      CGPoint startPoint = [[startPoints objectAtIndex:touchIndex] CGPointValue];
      CGPoint endPoint = [touch locationInView:touchedView];
      [trackingTouches removeObjectAtIndex:touchIndex];
      [startPoints removeObjectAtIndex:touchIndex];
      
      // detect short taps that are too small to contain any text;
      // these are probably accidents
      if (distanceBetween(startPoint, endPoint) < 50.0) return;
      
      CGRect rect = CGRectMake(startPoint.x, startPoint.y, endPoint.x - startPoint.x, endPoint.y - startPoint.y);
      self.completedPath = [UIBezierPath bezierPathWithRect:rect];
      
      // draw a shaded area over the entire view, so that the user can
      // easily see where to focus their attention.
      UIView *backgroundShade = [[[UIView alloc] initWithFrame:touchedView.bounds] autorelease];
      backgroundShade.backgroundColor = [UIColor colorWithWhite:0.0 alpha:0.5];
      backgroundShade.tag = SHADE_TAG;
      backgroundShade.userInteractionEnabled = NO;
      [touchedView addSubview:backgroundShade];
      
      // now comes the fun part.  we make a temporary UITextView for the
      // actual text input.
      UITextView *textView = [[[UITextView alloc] initWithFrame:rect] autorelease];
      textView.font = delegate.font;
      [[NSNotificationCenter defaultCenter] addObserver:self selector:@selector(keyboardDidShow:) name:UIKeyboardDidShowNotification object:nil];
      [[NSNotificationCenter defaultCenter] addObserver:self selector:@selector(keyboardWillShow:) name:UIKeyboardWillShowNotification object:nil];
      [[NSNotificationCenter defaultCenter] addObserver:self selector:@selector(keyboardDidHide:) name:UIKeyboardDidHideNotification object:nil];
      [[NSNotificationCenter defaultCenter] addObserver:self selector:@selector(keyboardWillHide:) name:UIKeyboardWillHideNotification object:nil];
      
      // in case the chosen view is going to be below the keyboard, we need to
      // make an effort to determine how far the display area should slide when
      // the keyboard is going to be shown.
      //
      // keyboard heights:
      //
      // 352 landscape
      // 264 portrait
      CGFloat keyboardHeight = 0;
      UIInterfaceOrientation orientation = ((UIViewController*)delegate).interfaceOrientation;
      if (UIInterfaceOrientationIsPortrait(orientation)) {
        keyboardHeight = 264;
      } else {
        keyboardHeight = 352;
      }
      CGRect viewBounds = touchedView.bounds;
      CGFloat rectMaxY = rect.origin.y + rect.size.height;
      CGFloat availableHeight = viewBounds.size.height - keyboardHeight;
      if (rectMaxY > availableHeight) {
        // calculate a slide distance so that the dragged box is centered vertically
        viewSlideDistance = rectMaxY - availableHeight;
      } else {
        viewSlideDistance = 0;
      }
      
      textView.delegate = self;
      [touchedView addSubview:textView];
      textView.editable = NO;
      textView.editable = YES;
      [textView becomeFirstResponder];
    }
  }
}

首先得到起点，终点，然后清空数组

if (distanceBetween(startPoint, endPoint) < 50.0) return; 进行了一个判断，防止用户画的矩形太小，影响输入文字，

如果大小没问题，接下来便将最终的矩形路径赋值到 self.completedPath 在退出此方法后进入drawTemporary后就会进入if分支

接着画出灰色的背景，此处的设置透明度为0.5, 并且为背景view设置tag为SHADE_TAG 这个标记用来在以后编辑完成的时候通过 viewWithTag方法找到这个背景的实例并且移除它

接下来便开始创建textView 其frame就是刚在最终得到的矩形路径的位置信息

接着注册了一些通知，即在键盘弹出，或者落下的时候调用的几个方法

下面的一部分代码实现的功能是如果键盘弹出可能会挡住 textView 判断是否挡住了如果挡住了需要向上移动多少距离，并且将这个距离赋值给全局的变量viewSlideDistance 如果没有挡住设置为0

最后将textView显示出来，并且通过[textView becomeFirstResponder]; 在其刚显示的时候马上成为第一响应者，弹出键盘

下面两个方法在键盘弹出之前以及落下之前，调用移动视图，防止textView 被挡

- (void)keyboardWillShow:(NSNotification *)aNotification {	
  UIInterfaceOrientation orientation = ((UIViewController*)delegate).interfaceOrientation;
	[UIView beginAnimations:@"viewSlideUp" context:NULL];
  UIView *view = [delegate viewForUseWithTool:self];
  CGRect frame = [view frame];
  switch (orientation) {
    case UIInterfaceOrientationLandscapeLeft:
      frame.origin.x -= viewSlideDistance; 
      break;
    case UIInterfaceOrientationLandscapeRight:
      frame.origin.x += viewSlideDistance; 
      break;
    case UIInterfaceOrientationPortrait:
      frame.origin.y -= viewSlideDistance; 
      break;
    case UIInterfaceOrientationPortraitUpsideDown:
      frame.origin.y += viewSlideDistance; 
      break;
    default:
      break;
  }
  [view setFrame:frame];
	[UIView commitAnimations];
}
- (void)keyboardWillHide:(NSNotification *)aNotification {
  UIInterfaceOrientation orientation = ((UIViewController*)delegate).interfaceOrientation;
	[UIView beginAnimations:@"viewSlideDown" context:NULL];
  UIView *view = [delegate viewForUseWithTool:self];
  CGRect frame = [view frame];
  switch (orientation) {
    case UIInterfaceOrientationLandscapeLeft:
      frame.origin.x += viewSlideDistance; 
      break;
    case UIInterfaceOrientationLandscapeRight:
      frame.origin.x -= viewSlideDistance; 
      break;
    case UIInterfaceOrientationPortrait:
      frame.origin.y += viewSlideDistance; 
      break;
    case UIInterfaceOrientationPortraitUpsideDown:
      frame.origin.y -= viewSlideDistance; 
      break;
    default:
      break;
  }
  [view setFrame:frame];
	[UIView commitAnimations];
}

当我们编辑完了内容后我们可以点击屏幕的其他地方（我们设置了［dudelView endEditing:YES］）或者点击键盘上的落下键盘按钮这时进入textView的 delegate

- (void)textViewDidEndEditing:(UITextView *)textView {
  //NSLog(@"textViewDidEndEditing");
  TextDrawingInfo *info = [TextDrawingInfo textDrawingInfoWithPath:completedPath text:textView.text strokeColor:delegate.strokeColor font:delegate.font];
  [delegate addDrawable:info];
  self.completedPath = nil;
  UIView *superView = [textView superview];
  [[superView viewWithTag:SHADE_TAG] removeFromSuperview];
  [textView resignFirstResponder];
  [textView removeFromSuperview];
  [[NSNotificationCenter defaultCenter] removeObserver:self];
}

这里用到了一个新类TextDrawingInfo 同上一章的PathDrawingInfo 类似，都是存放一个完整操作的全部信息，由于上一章我们做的是绘图操作，因此PathDrawingInfo 存放的是每次绘图操作的信息，而这次我们主要向利用coreText在屏幕上显示文字那么之前绘制的矩形的信息此时已经没有用我门要取得 CoreText 需要的信息，即我们这次文字操作的信息存到TextDrawingInfo 中去并且添加到 dudelView 的 drawables中最后将没用的东西全部从屏幕上移除

最后看以下 TextDrawingInfo 中的draw方法是怎么把文字绘制上去的

- (void)draw {
  CGContextRef context = UIGraphicsGetCurrentContext();

  NSMutableAttributedString *attrString = [[[NSMutableAttributedString alloc] initWithString:self.text] autorelease];
  [attrString addAttribute:(NSString *)(kCTForegroundColorAttributeName) value:(id)self.strokeColor.CGColor range:NSMakeRange(0, [self.text length])];
  
  CTFramesetterRef framesetter = CTFramesetterCreateWithAttributedString((CFAttributedStringRef)attrString);
  
  CTFrameRef frame = CTFramesetterCreateFrame(framesetter, CFRangeMake(0, [attrString length]), self.path.CGPath, NULL);
  CFRelease(framesetter);
  //CFRelease(attrString);
  if (frame) {
    CGContextSaveGState(context);
    
    // Core Text wants to draw our text upside-down!  This flips it the 
    // right way.
    CGContextTranslateCTM(context, 0, path.bounds.origin.y);
    CGContextScaleCTM(context, 1, -1);
    CGContextTranslateCTM(context, 0, -(path.bounds.origin.y + path.bounds.size.height));

    CTFrameDraw(frame, context);

    CGContextRestoreGState(context);

    CFRelease(frame);
  }
}

首先获得当前的上下文

创建一个属性自字符串NSMutableAttributedString 并设置他的颜色以及其他属性

利用该属性字符串创建一个CTFramesetterRef

再创建一个CTFrameRef

释放之前创建的CTFramesetterRef 对象framesetter

由于CoreText 是来自于Mac OS X的它在绘图的时候认为坐标轴是倒置的，所以在没ios中会产生倒置的效果，这里要转化以下才能正常显示

学习这一章主要学习它的思路怎么实现在一个view上画出一个矩形框后就是一个testView 并且编辑完成后在相应的位置相识出编辑的内容当然我们也可以利用一些其他的图文混排的库比如DTcoreText