ios - 如何继续drawRect : when finger on screen
<p><p>我有当前代码:</p>
<pre><code>- (void) touchesMoved:(NSSet *)touches withEvent:(UIEvent *)event {
self.objectPoint = [ locationInView:self];
float x, y;
if (self.objectPoint.x > self.objectPoint.x) {
x = self.objectPoint.x + 1;
}
else x = self.objectPoint.x - 1;
if (self.fingerPoint.y > self.objectPoint.y) {
y = self.objectPoint.y + 1;
}
else y = self.minionPoint.y - 1;
self.objectPoint = CGPointMake(x, y);
;
}
</code></pre>
<p>我的问题是我想让对象跟随您的手指，直到您将手指从屏幕上移开。只有当我的手指移动时它才会跟随。 <code>touchesEnded</code> 仅在我将手指从屏幕上移开时才起作用，所以这也不是我想要的。如何启用可以解决我的问题的功能？</p></p>
<br><hr><h1><strong>Best Answer-推荐答案</ strong></h1><br>
<p><p>如果您想触摸屏幕的某个部分，并且只要您的手指一直向下，就想朝那个方向移动绘制的对象，有几种方法。 </p>
<p>On 方法是使用某种形式的计时器，当用户将手指放在屏幕上时，它会重复调用一个方法(因为，正如您所指出的，您只会获得对 <code>touchesMoved</的更新</code>移动时)。虽然 <code>NSTimer</code> 是您遇到的最常见的计时器，但在这种情况下，您需要使用一个称为显示链接的专用计时器，即 <code>CADisplayLink</code>，它会触发何时可以执行屏幕更新。所以，你会:</p>
<ul>
<li><p>在<code>touchesBegan</code>中，捕捉用户在屏幕上触摸的位置并启动<code>CADisplayLink</code>；</p></li>
<li><p>在 <code>touchesMoved</code> 中，您将更新用户的触摸位置(但仅在他们移动手指时调用)；</p></li>
<li><p>在 <code>touchesEnded</code> 中，您可能会停止显示链接；和</p></li>
<li><p>在您的 <code>CADisplayLink</code> 处理程序中，您将更新位置(并且您需要知道您希望它移动的速度)。</p></li >
</ul>
<p>所以，这看起来像:</p>
<pre><code>- (void)touchesBegan:(NSSet *)touches withEvent:(UIEvent *)event
{
self.velocity = 100.0; // 100 points per second
self.touchLocation = [ locationInView:self];
;
}
- (void)touchesMoved:(NSSet *)touches withEvent:(UIEvent *)event
{
self.touchLocation = [ locationInView:self];
}
- (void)touchesEnded:(NSSet *)touches withEvent:(UIEvent *)event
{
;
}
- (void)startDisplayLink
{
self.displayLink = ;
self.lastTimestamp = CACurrentMediaTime(); // initialize the `lastTimestamp`
forMode:NSDefaultRunLoopMode];
}
- (void)stopDisplayLink
{
;
self.displayLink = nil;
}
- (void)handleDisplayLink:(CADisplayLink *)displayLink
{
// figure out the time elapsed, and reset the `lastTimestamp`
CFTimeInterval currentTimestamp = CACurrentMediaTime();
CFTimeInterval elapsed = currentTimestamp - self.lastTimestamp;
self.lastTimestamp = currentTimestamp;
// figure out distance to touch and distance we'd move on basis of velocity and elapsed time
CGFloat distanceToTouch= hypotf(self.touchLocation.y - self.objectPoint.y, self.touchLocation.x - self.objectPoint.x);
CGFloat distanceWillMove = self.velocity * elapsed;
// this does the calculation of the angle between the touch location and
// the current `self.objectPoint`, and then updates `self.objectPoint` on
// the basis of (a) the angle; and (b) the desired velocity.
if (distanceToTouch == 0.0) // if we're already at touchLocation, then just quit
return;
if (distanceToTouch < distanceWillMove) { // if the distance to move is less than the target, just move to touchLocation
self.objectPoint = self.touchLocation;
} else { // otherwise, calculate where we're going to move to
CGFloat angle = atan2f(self.touchLocation.y - self.objectPoint.y, self.touchLocation.x - self.objectPoint.x);
self.objectPoint = CGPointMake(self.objectPoint.x + cosf(angle) * distanceWillMove,
self.objectPoint.y + sinf(angle) * distanceWillMove);
}
;
}
</code></pre>
<p>要使用它，您需要定义一些属性:</p>
<pre><code>@property (nonatomic) CGFloat velocity;
@property (nonatomic) CGPoint touchLocation;
@property (nonatomic, strong) CADisplayLink *displayLink;
@property (nonatomic) CFTimeInterval lastTimestamp;
</code></pre></p>
<p style="font-size: 20px;">关于ios - 如何继续drawRect : when finger on screen，我们在Stack Overflow上找到一个类似的问题：
<a href="https://stackoverflow.com/questions/22826244/" rel="noreferrer noopener nofollow" style="color: red;">
https://stackoverflow.com/questions/22826244/
</a>
</p>
页:
[1]