Databases
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PO
 

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    <p>For loading images from the network there are two obvious failure cases:</p> <ol> <li>The downloaded file was not an image at all.</li> <li>The downloaded data only contains part of the image data.</li> </ol> <p>For the first case nil checking the return value of various UIImage methods is probably the best way to handle this error case.</p> <p>The following class methods on <code>UIImage</code> will return nil if the image could not be initialized with the data it was provided: <code>+ (UIImage *)imageWithData:(NSData *)data</code> and <code>+ (UIImage *)imageWithContentsOfFile:(NSString *)path</code>.</p> <p>Code that does the nil check might look like this:</p> <pre><code>UIImage *image = [UIImage imageWithContentsOfFile:pathToImage]; if (image) { // The image was loaded. Display it } else { // The image was not loaded. Redownload or display a placeholder, etc... } </code></pre> <p>For the second failure case it is likely the result of lost connection. For this case the failure is best handled in the NSURLConnection's delegate. When downloading the image if <code>- (void)connection:(NSURLConnection *)connection didFailWithError:(NSError *)error</code> is called then the data for the request should be discarded. </p> <p>Also keep in mind that <code>didFailWithError:</code> will not be called for 4xx or 5xx responses from the server. It is called when the connection is cut off for other reasons. It would generally be a good idea to make sure you only write image data to disk when the server has responded with a 200 OK.</p>
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    1. POHow to Check if an image is valid on iPhone
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    1. CONo, if the header of image is well, then it can be initialized as an UIImage and then display half
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    2. COI have updated the answer on how to deal with two common failure cases. Only checking the image itself is hard because you have to deal with all the different formats individually. Hard, annoying and generally not worth it.
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Detail views are divided into sections. All the information in the data section comes from columns in the selected row. The other sections display data from other, related rows.

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Try moving around until you find a non-empty to-many entry and click on the label to get to one. You can move back to the root by clicking on the database name in the header.

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