如何动态处理图像平铺

Question

我正在编写一个应用程序，它将平铺图像 256 * 256 并将这些平铺文件写回到目录中。如果有任何更新，我每次都会更新我的 URL，并将这些图像平铺回来并存储在 iphone 文件夹中。我主要担心两件事： 1）内存消耗——5张大小为200KB的图像的内存消耗会很多吗？ 2) 如果我必须同时使用图像平铺 5 个不同的 URL，我可以多快处理我的应用程序？

我已经编写了一段代码来平铺并保存在一个 URL 的目录中，并且希望对 5 个 URL 执行相同的操作。是否建议采用这种方法，或者是否有人有不同的方法？

    - (void)viewDidLoad
    {
      [super viewDidLoad];

      NSString *URLString = @"http://www.abc.com/abc.html?event=123";   
      NSURL *url = [[NSURL alloc] initWithString:URLString];
      NSData * dataImage = [NSData dataWithContentsOfURL:url];

      NSString *directoryPath = [[NSBundle mainBundle] bundlePath];

      UIImage *big = [UIImage imageWithData:dataImage];
      [self saveTilesOfSize:(CGSize){256,256} forImage:big toDirectory:directoryPath          usingPrefix:@"image_124_"];  

       TileView *tv = [[TileView alloc] initWithFrame:(CGRect){{0,0}, (CGSize){5000,5000}}];
      [tv setTileTag:@"image_110_"];
      [tv setTileDirectory:directoryPath];

      [scrollView addSubview:tv];

      [scrollView setContentSize:(CGSize){5000,5000}];
    }


     - (void)saveTilesOfSize:(CGSize)size 
        forImage:(UIImage*)image 
        toDirectory:(NSString*)directoryPath 
        usingPrefix:(NSString*)prefix
     {
      CGFloat cols = [image size].width / size.width;
      CGFloat rows = [image size].height / size.height;

      int fullColumns = floorf(cols);
      int fullRows = floorf(rows);

      CGFloat remainderWidth = [image size].width - 
                      (fullColumns * size.width);
      CGFloat remainderHeight = [image size].height - 
                      (fullRows * size.height);


      if (cols > fullColumns) fullColumns++;
      if (rows > fullRows) fullRows++;

      CGImageRef fullImage = [image CGImage];

      for (int y = 0; y < fullRows; ++y) {
       for (int x = 0; x < fullColumns; ++x) {
       CGSize tileSize = size;
       if (x + 1 == fullColumns && remainderWidth > 0) {
       // Last column
       tileSize.width = remainderWidth;
       }

       if (y + 1 == fullRows && remainderHeight > 0) {
       // Last row
       tileSize.height = remainderHeight;
       }

       CGImageRef tileImage = CGImageCreateWithImageInRect(fullImage, 
                                    (CGRect){{x*size.width, y*size.height}, 
                                      tileSize});

        NSData *imageData = UIImagePNGRepresentation([UIImage imageWithCGImage:tileImage]);
       NSString *path = [NSString stringWithFormat:@"%@/%d.png", 
                    directoryPath, prefix];
  [imageData writeToFile:path atomically:NO];
 }
}    
}

Answer 1

我已经用不同的方法实现了类似问题的解决方案（不同的是，我没有将它们保存在目录中，这些仅用于显示目的。）。

在我的问题中，我有 84 个尺寸为 250x250 的图像，每个图像大小为 8KB（我将它们添加到 scrollView 上，并在滚动时加载它们，有点类似于谷歌地图，但是更顺畅）。起初我使用与你相同的方法，但性能有问题。所以，我使用了异步加载的概念。我编写了一个带有连接委托的 UIImageView 子类，因此 UIImageView 子类负责加载其图像。由于加载是异步的，因此性能要好得多。

正如您所问的

1）内存消耗 - 5 个大小为 200 KB 的图像的内存消耗会很多吗？

Ans：5x200KB = 1MB ~ 1.2MB 左右（所以你需要那么多内存来显示，如果你有那么多内存，那么你不用担心。）..在我的例子中，84x8KB = 672 ~ 900KB（因为我正在使用一些额外的东西，比如每个图像视图的活动指示器）。

2）如果我必须同时使用图像平铺 5 个不同的 URL，我可以多快处理我的应用程序？

Ans：当您在 viewDidLoad 中加载它时...或者在主线程中，那么性能将成为一个问题（可能会发生阻塞，因为我不完全确定您是否正在使用线程）。

快速建议：

1. write an UIImageView subclass which has connection delegate methods.
2. have some method that you can call from outside to message this imageView to start loading.(give the url)
3. do proper deallocation of resources like responseData and connection object, once the downloading is complete.
4. when you move from this view to other view do proper deallocation and removal of all these imageviews.
5. use intruments to look for the allocations by this.

代码：

TileImageView.h

@interface TileImageView : UIImageView 
{
    NSURLConnection *serverConnection;
    BOOL isImageRequested;
    NSMutableData *responseData;

}
-(void) startImageDownloading:(NSString *)pRequestURL
-(void) deallocateResources;
-(BOOL) isImageRequested;
-(void)cancelConnectionRequest;

-(void) addActivityIndicator;
-(void) removeActivityIndicator;
@end

< code>TileImageView.m

@implementation TileImageView


- (id)initWithFrame:(CGRect)frame {

    self = [super initWithFrame:frame];
    if (self) 
    {
        // Initialization code.
        isImageRequested = NO;

    }
    return self;
}

-(BOOL) isImageRequested
{
    return isImageRequested;
}

-(void) startImageDownloading:(NSString *)pRequestURL
{


    if (!isImageRequested)
    {



        NSURL *pServerURL = [[NSURL alloc] initWithString:pRequestURL];
        if (pServerURL != nil) 
        {
            isImageRequested = YES;
            [self addActivityIndicator];
            [self setBackgroundColor:[UIColor lightGrayColor]];
            NSURLRequest *pServerRequest = [[NSURLRequest alloc]initWithURL:pServerURL];
            serverConnection = [[NSURLConnection alloc] initWithRequest:pServerRequest delegate:self];
            if(serverConnection)
            {
                responseData = [[NSMutableData alloc] init];
            }
            [pServerURL release];
            [pServerRequest release];
        }


    }

}

-(void) addActivityIndicator
{
    UIActivityIndicatorView *tempActivityIndicator = [[UIActivityIndicatorView alloc] initWithActivityIndicatorStyle:UIActivityIndicatorViewStyleWhite];
    CGFloat size = self.frame.size.width*0.12;
    [tempActivityIndicator setFrame:CGRectMake(0, 0, size, size)];
    [tempActivityIndicator setCenter:CGPointMake(self.frame.size.width/2, self.frame.size.height/2)];
    [tempActivityIndicator setTag:1000];
    [tempActivityIndicator setHidesWhenStopped:YES];
    [tempActivityIndicator startAnimating];
    [self addSubview:tempActivityIndicator];
    [tempActivityIndicator release];
}

-(void) removeActivityIndicator
{
    UIActivityIndicatorView *tempActivityIndicator = (UIActivityIndicatorView *)[self viewWithTag:1000];
    if (tempActivityIndicator != nil)
    {
        [tempActivityIndicator stopAnimating];
        [tempActivityIndicator removeFromSuperview];
    }
}


-(void)cancelConnectionRequest
{
    if (isImageRequested && serverConnection != nil)
    {
        [serverConnection cancel];
        [self removeActivityIndicator];
        [self deallocateResources];
        isImageRequested = NO;
    }

}



// Name         :   connection: didReceiveAuthenticationChallenge:
// Description  :   NSURLConnectionDelegate method. Method that gets called when server sends an authentication challenge.
- (void)connection:(NSURLConnection *)connection didReceiveAuthenticationChallenge:(NSURLAuthenticationChallenge *)challenge 
{
    if ([challenge.protectionSpace.authenticationMethod isEqualToString:NSURLAuthenticationMethodServerTrust])
    {
        [challenge.sender useCredential:[NSURLCredential credentialForTrust:challenge.protectionSpace.serverTrust] forAuthenticationChallenge:challenge];
    }
    [challenge.sender continueWithoutCredentialForAuthenticationChallenge:challenge];
}

// Name         :   connection: didReceiveResponse:
// Description  :   NSURLConnectionDelegate method. Method that gets called when response for the launched URL is received..
-(void) connection:(NSURLConnection *) connection didReceiveResponse:(NSURLResponse *) response 
{
    [responseData setLength:0]; 

}

// Name         :   connection: didReceiveData:
// Description  :   NSURLConnectionDelegate method. Method that gets called when data for the launched URL is received..
-(void) connection:(NSURLConnection *) connection didReceiveData:(NSData *) data 
{
    [responseData appendData:data];
}

// Name         :   connection: didFailWithError:
// Description  :   NSURLConnectionDelegate method. Method that gets called when an error for the launched URL is received..
-(void) connection:(NSURLConnection *) connection didFailWithError:(NSError *) error 
{
    NSLog(@"Error occured while loading image : %@",error);
    [self removeActivityIndicator];
    [self deallocateResources];


    UILabel *tempLabel = [[UILabel alloc] initWithFrame:CGRectMake(0, 0, 150, 30)];
    [tempLabel setBackgroundColor:[UIColor clearColor]];
    [tempLabel setFont:[UIFont systemFontOfSize:11.0f]];
    [tempLabel setCenter:CGPointMake(self.frame.size.width/2, self.frame.size.height/2)];
    [tempLabel setText:@"Image not available."];
    [self addSubview:tempLabel];
    [tempLabel release];

}

// Name         :   connectionDidFinishLoading
// Description  :   NSURLConnectionDelegate method. Method that gets called when connection loading gets finished.
-(void) connectionDidFinishLoading:(NSURLConnection *) connection 
{
    [self removeActivityIndicator];
    UIImage *tempImage = [[UIImage alloc] initWithData:responseData];
    self.image = tempImage;
    [tempImage release];
    [self deallocateResources];
}

-(void) deallocateResources
{

    if (serverConnection != nil) 
    {
        [serverConnection release];
        serverConnection = nil;
    }
    if (responseData != nil)
    {
        [responseData release];
        responseData = nil;
    }
}

- (void)dealloc {
    [super dealloc];
}


@end

所以，如果您使用上面的代码，那么您只需添加 TileImageView 对象并调用方法 -(void) startImageDownloading :(NSString *)pRequestURL。

Please use instruments to track allocations.

更新：

**How do I add TileImageView on scrollView ? :**

//像这样，我在 2D 形状（12 x 7）网格中添加 84 个图像...添加图像后，我根据完整的网格大小设置滚动视图的 contentSize。

TileImageView *tileImageView  = [[TileImageView alloc]initWithFrame:<myFrameAsPerMyNeeds>];
[tileImageView setTag:<this is the identifier I use for recognizing the image>];
[myImageScrollView addSubView:tileImageView];
[tileImageView release];

..稍后在代码中，当用户滚动和其他图像视图可见时。我使用以下代码...

TileImageView *loadableImageView = (TileImageView *)[myImageScrollView viewWithTag:];
[loadableImageView开始图像下载：];

我不需要在 drawRect: 中执行任何操作，因为我不需要进行自定义绘图。

对于图像名称，您可以使用 imageView 中的标签属性，但如果您需要一些更像字符串的不同名称，那么您可以在 imageView 中为图像名称放置另一个属性并设置它同时添加图像视图。为了保存数据，您可以在 TileImageView 的 didFinishLoading 方法中下载图像后调用您的方法，您可以在其中使用该名称。

第二次更新

添加 TileImageView

gridCount = 0;
rows = 7;
columns = 12;
totalGrids = rows*columns;
//*above : all are NSInteger type variable declared at class level

chunkWidth = 250;
chunkHeight = 250;
contentWidth = 0.0;
contentHeight = 0.0;
//*above : all are CGFloat type variable declared at class level
for (int i=0; i<rows; i++) 
{
    contentWidth = 0.0;
    for (int j=0 ; j<columns; j++)
    {

        gridCount++;
        CGRect frame = CGRectMake(contentWidth, contentHeight, chunkWidth, chunkHeight);
        [self addNewImageViewWithTag:gridCount frame:frame];
        contentWidth += chunkWidth;
    }
    contentHeight += chunkHeight;
}

[imageScrollView setContentSize:CGSizeMake(contentWidth, contentHeight)];
[imageScrollView setContentOffset:CGPointMake(0, 0)];
[imageScrollView setUserInteractionEnabled:YES];

我如何在 ScrollView和 ScrollViewDelegate 方法中

- (void) scrollViewDidScroll:(UIScrollView *)scrollView
{
    if (isZoomed)
    {
        xOffset = scrollView.contentOffset.x;
        yOffset = scrollView.contentOffset.y;
        //*above : both are CGFloat type variable declared at class level

        visibleColumn = xOffset/chunkWidth+1;
        visibleRow = yOffset/chunkHeight+1;
        gridNumber = (visibleRow-1)*columns+visibleColumn;
        adjGrid1 = gridNumber+1;
        adjGrid2 = gridNumber+columns;
        adjGrid3 = adjGrid2+1;
        //*above : all are NSInteger type variable declared at class level
        if (gridNumber ==1)
        {
            [self createAndSendScrollRequest:gridNumber];
        }
        if (adjGrid1 > 0 && adjGrid1 <= totalGrids) 
        {
            [self createAndSendScrollRequest:adjGrid1];
        }
        if (adjGrid2 > 0 && adjGrid2 <= totalGrids) 
        {
            [self createAndSendScrollRequest:adjGrid2];
        }
        if (adjGrid3 > 0 && adjGrid3 <= totalGrids) 
        {
            [self createAndSendScrollRequest:adjGrid3];
        }
    }


}

。这就是createAndSendScrollRequest 的实现方式。

- (void) createAndSendScrollRequest:(NSInteger)chunkId
{

    TileImageView *loadingImageView = (TileImageView *)[imageScrollView viewWithTag:chunkId];
    if ([loadingImageView image]==nil) 
    {
        [loadingImageView startImageDownloading:<and here I pass url my url is based on tag so In reality I dont pass anything I just use it from the imageview's tag property>];
    }

}

谢谢，