Question

构建一个应用程序，让用户可以选择更改应用程序的背景。目前使用此代码保存选择器中的图像。

- (void)imagePickerController:(UIImagePickerController *)picker didFinishPickingMediaWithInfo:(NSDictionary *)info
{
    customImage = [info objectForKey:UIImagePickerControllerOriginalImage];

    NSData *data = UIImagePNGRepresentation(customImage);
    NSString *fetchCustomImage = @"userCustomImage.png";
    NSArray *path = NSSearchPathForDirectoriesInDomains(NSDocumentDirectory, NSUserDomainMask, YES);
    NSString *documentDirectory = [path objectAtIndex:0];
    NSString *fullPathToFile = [documentDirectory stringByAppendingPathComponent:fetchCustomImage];

    [data writeToFile:fullPathToFile atomically:YES];

    [self dismissViewControllerAnimated:YES completion:NULL];

    [self performSelector:@selector(fetchCustomBackground)]
}

然后调用void来显示图像

- (void)fetchCustomBackground
{
    //Fetch Background Image
    NSString *fetchUserImage = @"userCustomImage.png";
    NSArray *path = NSSearchPathForDirectoriesInDomains(NSDocumentDirectory, NSUserDomainMask, YES);
    NSString *documentDirectory = [path objectAtIndex:0];
    NSString *fullPath = [documentDirectory stringByAppendingPathComponent:fetchUserImage];
    NSData *data = [NSData dataWithContentsOfFile:fullPath];
    [background setImage:[UIImage imageWithData:data]];

}

在viewDidLoad

中

[self performSelector:@selector(fetchCustomBackground)];

目前应用程序非常慢，我猜是因为每次加载视图都需要获取图像，有没有办法保存它，所以你不必每次加载视图时调用它？

Answer 1

我发现从Documents加载单张图片没问题。但可以肯定的是，如果您正在加载大图并同时执行一些UI更新，则可能会出现问题。你必须使用Grand Central Dispatch释放主线程。

Answer 2

尝试更新您的功能。

- (void)fetchCustomBackground
{

dispatch_queue_t concurrentQueue = dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, 0);
dispatch_async(concurrentQueue, ^{

__block NSData *data;

dispatch_sync(concurrentQueue, ^{ 
    //Fetch Background Image
    NSString *fetchUserImage = @"userCustomImage.png";
    NSArray *path = NSSearchPathForDirectoriesInDomains(NSDocumentDirectory, NSUserDomainMask, YES);
    NSString *documentDirectory = [path objectAtIndex:0];
    NSString *fullPath = [documentDirectory stringByAppendingPathComponent:fetchUserImage];
    data = [NSData dataWithContentsOfFile:fullPath];
});
dispatch_sync(dispatch_get_main_queue(), ^{
[background setImage:[UIImage imageWithData:data]];
}); });
}

来自UIIMAGEPickerController的自定义背景图像

2 个答案: