Question

相当常见的问题，我有几个答案，我几乎就在那里。我有一个按钮，按下后，将创建一个图像（代码如下）

（numImages在加载时设置为ZERO，用作所有图像的标记号的计数）

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，它将检测触摸的内容。我需要它做的是允许用户拖动新创建的图像。它几乎可以正常工作，但拖动它时图像会闪烁不已。我可以访问你点击的图像，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，当我点击它们时，我会得到每个图像的标记输出。但是当我拖动时，它闪烁......任何想法？

Answer 1

在回答我自己的问题时 - 我决定创建一个类来处理我放在视图上的图像。

代码，如果有人感兴趣....

Draggable.h

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

Draggable.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

并称之为

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

通常在更改center时会获得隐式动画。您是否正在弄乱-contentMode或任何机会致电-setNeedsDisplay？

您可以显式请求动画以避免删除并以这种方式重新绘制：

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要复杂得多），这会导致像{{{}}那样频繁出现问题{1}}。

顺便说一下，你正在泄漏touchesMoved:withEvent:。

UIImage检测触摸和拖动

2 个答案: