UIImage 检测触摸和拖动

Question

这是一个相当常见的问题，我有几个答案，而且我快到了。我有一个按钮，按下时会创建一个图像（代码如下）

（numImages 在加载时设置为零，并用作创建的所有图像的标签号的计数）

UIImage *tmpImage = [[UIImage imageNamed:[NSString stringWithFormat:@"%i.png", sender.tag]] retain];
UIImageView *myImage = [[UIImageView alloc] initWithImage:tmpImage];

numImages += 1;

myImage.userInteractionEnabled = YES;
myImage.tag = numImages;
myImage.opaque = YES;
[self.view addSubview:myImage];
[myImage release];

然后我有一个 touchesBegan 方法，它会检测触摸的内容。我需要它做的是允许用户拖动新创建的图像。它几乎可以工作，但是当您拖动它时，图像会在整个地方闪烁。我可以访问您单击的图像，因为我可以得到它的标签，但我不能很好地拖动它。

- (void) touchesBegan:(NSSet *)touches withEvent:(UIEvent *)event {

    UITouch *touch = [[event allTouches] anyObject];
    CGPoint location = [touch locationInView:touch.view];

    if (touch.view.tag > 0) {
        touch.view.center = location;
    }

    NSLog(@"tag=%@", [NSString stringWithFormat:@"%i", touch.view.tag]);

}

- (void) touchesMoved:(NSSet *)touches withEvent: (UIEvent *)event {
    [self touchesBegan:touches withEvent:event];
}

它的工作原理是，当我单击它们时，我会为每个图像获得标签的输出。但是当我拖动时，它会闪烁……有什么想法吗？

Answer 1

回答我自己的问题 - 我决定创建一个类来处理我放置在视图上的图像。

如果有人感兴趣，请编码....

可拖动的.h

#import <Foundation/Foundation.h>
@interface Draggable : UIImageView {
    CGPoint startLocation;
}
@end

可拖动的.m

#import "Draggable.h"
@implementation Draggable

- (void) touchesBegan:(NSSet*)touches withEvent:(UIEvent*)event {
    // Retrieve the touch point
    CGPoint pt = [[touches anyObject] locationInView:self];
    startLocation = pt;
    [[self superview] bringSubviewToFront:self];
}
- (void) touchesMoved:(NSSet*)touches withEvent:(UIEvent*)event {
    // Move relative to the original touch point
    CGPoint pt = [[touches anyObject] locationInView:self];
    CGRect frame = [self frame];
    frame.origin.x += pt.x - startLocation.x;
    frame.origin.y += pt.y - startLocation.y;
    [self setFrame:frame];
}
@end

然后叫它

UIImage *tmpImage = [[UIImage imageNamed:"test.png"] retain];
UIImageView *imageView = [[UIImageView alloc] initWithImage:tmpImage];

CGRect cellRectangle;
cellRectangle = CGRectMake(0,0,tmpImage.size.width ,tmpImage.size.height );
UIImageView *dragger = [[Draggable alloc] initWithFrame:cellRectangle];
[dragger setImage:tmpImage];
[dragger setUserInteractionEnabled:YES];

[self.view addSubview:dragger];
[imageView release];
[tmpImage release];

Answer 2

当您更改center 时，通常会得到一个隐式动画。你是在惹-contentMode 还是打电话给-setNeedsDisplay？

您可以通过这种方式显式请求动画以避免删除和重新绘制：

if (touch.view.tag > 0) {
    [UIView beginAnimations:@"viewMove" context:touch.view];
    touch.view.center = location;
    [UIView commitAnimations];
}

请注意NSLog() 可能非常慢（比您预期的要慢得多；它比简单的printf 复杂得多），这可能会在像touchesMoved:withEvent: 这样经常调用的东西中造成麻烦。

顺便说一句，你在泄露tmpImage。