objective-c - iOS中的中断队列或文件写入操作
<p><p>我在 iPhone 上处理大图像，因此将它们保存到磁盘可能需要几秒钟的时间，有时当图像尚未完成保存时会出现删除图像的指令。我想中断保存过程并立即删除文件，而不是先等待它保存，但是我找不到任何方法来中断队列或保存操作。</p>
<pre><code>@interface YMSavedImage : NSObject {
UIImage *image;
NSString *path;
dispatch_queue_t imageAccess;
...
}
@end
@implementation YMSavedImage
- (id)init
{
...
imageAccess = dispatch_queue_create("imageAccessQueue", NULL);
...
}
- (void)save
{
dispatch_async(imageAccess, ^(void) {
;// This takes several seconds.
});
}
- (void)delete
{
dispatch_sync(imageAccess, ^(void) {
if () {
;
}
});
}
...
@end
</code></pre></p>
<br><hr><h1><strong>Best Answer-推荐答案</ strong></h1><br>
<p><p><code>writeToFile:atomically:</code> 想要一次性将所有数据写入文件。您最好捕获一个 <code>NSFileHandle</code> 并快速写入数据的子部分，在每次原子写入之后，您可以检查用户是否请求取消保存。</p>
<p>我建议如下:</p>
<pre><code>- (void)save
{
dispatch_async(imageAccess, ^{
// Create an empty file to populate
[ createFileAtPath:_imageFilePath contents:nil attributes:nil];
// Grab a handle on the file
NSFileHandle *handle = ;
NSData *imageData = UIImagePNGRepresentation(_image);
// Store how long the image is
NSUInteger totalLength = ;
// Store how many chunks we should need with the set kDesiredChunkSize
NSUInteger chunks = totalLength / kDesiredChunkSize;
NSUInteger i = 0;
// Walk through the image chunk by chunk and check if we are cancelled after each atomic operation
for (i = 0; i < chunks; i++) {
;
];
if (__userCancelledSave) { // The user asked us to cancel,
[ removeItemAtPath:_imageFilePath error:nil]; // FIXME: Handle this error
return;
}
}
// Write any remaining data that's less than one chunk in size
NSUInteger sizeDifference = totalLength - (chunks * kDesiredChunkSize);
if (sizeDifference > 0) {
;
];
}
});
}
</code></pre></p>
<p style="font-size: 20px;">关于objective-c - iOS中的中断队列或文件写入操作，我们在Stack Overflow上找到一个类似的问题：
<a href="https://stackoverflow.com/questions/7605017/" rel="noreferrer noopener nofollow" style="color: red;">
https://stackoverflow.com/questions/7605017/
</a>
</p>
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