[英]IOS: Loading image from parse.com into a tableview
我正在嘗試將關聯的圖像從解析加載到自定義表格單元格中。 當我執行代碼時,成功查詢了解析,並且正確顯示了表格單元格的其他信息,如書名和作者,但是當我嘗試添加圖像時,應用程序崩潰了。
這是我用來獲取圖像數據的代碼。
-(void)queryForNewBooks{
_bookNameArray = [[NSMutableArray alloc] init];
_authorNameArray = [[NSMutableArray alloc] init];
_isbnNumberArray = [[NSMutableArray alloc] init];
_bookImageData = [[NSMutableArray alloc] init];
PFQuery *query = [PFQuery queryWithClassName:@"BooksForSale"];
[query orderByDescending:@"createdAt"];
[query findObjectsInBackgroundWithBlock:^( NSArray *objects, NSError *error) {
if (objects.count >=1) {
for (PFObject *object in objects) {
PFFile *imageFile = [object objectForKey:@"image"];
[imageFile getDataInBackgroundWithBlock:^(NSData *result, NSError *error) {
if (!error) {
NSData *data = result;
NSLog(@"HEYYYYYY");
[ _bookImageData addObject:data];
}
}];
這是表格單元格代碼
- (UITableViewCell *)tableView:(UITableView *)tableView cellForRowAtIndexPath:(NSIndexPath *)indexPath
{
static NSString *simpleTableIdentifier = @"TableViewCell";
TableViewCell *cell = (TableViewCell *)[tableView dequeueReusableCellWithIdentifier:simpleTableIdentifier];
if (cell == nil)
{
NSArray *nib = [[NSBundle mainBundle] loadNibNamed:@"TableViewCell" owner:self options:nil];
cell = [nib objectAtIndex:0];
}
NSLog(@"Here are the book names, %@",_bookNameArray);
cell.bookNameLabel.text = [_bookNameArray objectAtIndex:indexPath.row];
cell.authorNameLabel.text = [_authorNameArray objectAtIndex:indexPath.row];
UIImage *image = [UIImage imageWithData: [_bookImageData objectAtIndex:indexPath.row]];
cell.bookImageLabel.image = image;
return cell;
}
我相信正是這兩條線引起了這個問題
UIImage *image = [UIImage imageWithData: [_bookImageData objectAtIndex:indexPath.row]];
cell.bookImageLabel.image = image;
當我評論這兩行時,應用程序不會崩潰。
任何人都可以提供關於我做錯的建議嗎?
謝謝
錯誤日志:
*** Terminating app due to uncaught exception 'NSRangeException', reason: '*** -[__NSArrayM objectAtIndex:]: index 0 beyond bounds for empty array' *** First throw call stack: ( 0 CoreFoundation 0x000000010f951f45 __exceptionPreprocess + 165 1 libobjc.A.dylib 0x000000010f3cbdeb objc_exception_throw + 48 2 CoreFoundation 0x000000010f8359e4 -[__NSArrayM objectAtIndex:] + 212 3 ParseStarterProject 0x000000010c45fd41 -[ParseStarterProjectViewController tableView:cellForRowAtIndexPath:] + 753 4 UIKit 0x000000010dba9e2a -[UITableView _createPreparedCellForGlobalRow:withIndexPath:willDisplay:] + 782 5 UIKit 0x000000010dba9f3f -[UITableView _createPreparedCellForGlobalRow:willDisplay:] + 74 6 UIKit 0x000000010db7f307 -[UITableView _updateVisibleCellsNow:isRecursive:] + 3187 7 UIKit 0x000000010dbb2d1c -[UITableView _performWithCachedTraitCollection:] + 92 8 UIKit 0x000000010db9a884 -[UITableView layoutSubviews] + 223 9 UIKit 0x000000010db08e40 -[UIView(CALayerDelegate) layoutSublayersOfLayer:] + 710 10 QuartzCore 0x000000010cf4559a -[CALayer layoutSublayers] + 146 11 QuartzCore 0x000000010cf39e70 _ZN2CA5Layer16layout_if_neededEPNS_11TransactionE + 366 12 QuartzCore 0x000000010cf39cee _ZN2CA5Layer28layout_and_display_if_neededEPNS_11TransactionE + 24 13 QuartzCore 0x000000010cf2e475 _ZN2CA7Context18commit_transactionEPNS_11TransactionE + 277 14 QuartzCore 0x000000010cf5bc0a _ZN2CA11Transaction6commitEv + 486 15 QuartzCore 0x000000010cf5c37c _ZN2CA11Transaction17observer_callbackEP19__CFRunLoopObservermPv + 92 16 CoreFoundation 0x000000010f87d947 __CFRUNLOOP_IS_CALLING_OUT_TO_AN_OBSERVER_CALLBACK_FUNCTION__ + 23 17 CoreFoundation 0x000000010f87d8b7 __CFRunLoopDoObservers + 391 18 CoreFoundation 0x000000010f87350b __CFRunLoopRun + 1147 19 CoreFoundation 0x000000010f872e08 CFRunLoopRunSpecific + 488 20 GraphicsServices 0x0000000110f79ad2 GSEventRunModal + 161 21 UIKit 0x000000010da5430d UIApplicationMain + 171 22 ParseStarterProject 0x000000010c45dfbf main + 111 23 libdyld.dylib 0x00000001114fa92d start + 1 24 ??? 0x0000000000000001 0x0 + 1 ) libc++abi.dylib: terminating with uncaught exception of type NSException
看來數據沒有被添加到nsmutablearray中,這應該出現在這里
for (PFObject *object in objects) {
PFFile *imageFile = [object objectForKey:@"image"];
[imageFile getDataInBackgroundWithBlock:^(NSData *result, NSError *error) {
if (!error) {
NSData *data = result;
NSLog(@"HEYYYYYY");
[ _bookImageData addObject:data];
}
getDataInBackgroundWithBlock
是一個異步進程。 需要時間來收到回復。 所以在請求完成之前,你的_bookImageData是空數組。
在_bookImageData有數據之前, - (UITableViewCell *)tableView:(UITableView *)tableView cellForRowAtIndexPath:(NSIndexPath *)indexPath
正在調用- (UITableViewCell *)tableView:(UITableView *)tableView cellForRowAtIndexPath:(NSIndexPath *)indexPath
,並且BOOM你的應用程序崩潰了!
UIImage *image = [UIImage imageWithData: [_bookImageData objectAtIndex:indexPath.row]];
cell.bookImageLabel.image = image;
解決方案是
①通過以下方式接收_bookImageData后嘗試刷新tableview:[yourtableview reloadData]或類似的東西。
②在調用objectAtIndex之前,使用try .. catch或檢查_bookImageData,使應用程序不會崩潰。
推薦:使用一些placeHolder圖片讓你的應用程序更酷。 :)
@try {
UIImage *image = [UIImage imageWithData: [_bookImageData objectAtIndex:indexPath.row]];
cell.bookImageLabel.image = image;
} catch ...
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