为什么我要三次解雇这个UIAlertView？

我正在UILongPressGestureRecognizer上显示警告，我面临的问题是，每次我必须点击三次才能解除警报，而单击按钮时警报应该被解除。

由于这种exception行为，条目在核心数据中重复。

我使用的代码如下：

在cellForRowAtIndexPath中：

-(UITableViewCell *)tableView:(UITableView *)tableView cellForRowAtIndexPath:(NSIndexPath *)indexPath { // NSString * cellValue; if (tableView == listTable) { cellValue = [listVehicles objectAtIndex:indexPath.row]; } else { // handle search results table view cellValue = [filteredListItems objectAtIndex:indexPath.row]; } static NSString *CellIdentifier = @"vlCell"; VehicleListCell *cell = [tableView dequeueReusableCellWithIdentifier:CellIdentifier]; if (cell == nil) { NSLog(@"Cell Created"); NSArray *nibObjects = [[NSBundle mainBundle] loadNibNamed:@"VehicleListCell" owner:nil options:nil]; for (id currentObject in nibObjects) { if ([currentObject isKindOfClass:[VehicleListCell class]]) { cell = (VehicleListCell *)currentObject; } } UILongPressGestureRecognizer *pressRecongnizer = [[UILongPressGestureRecognizer alloc] initWithTarget:self action:@selector(tableCellPressed:)]; pressRecongnizer.minimumPressDuration = 0.5f; [cell addGestureRecognizer:pressRecongnizer]; [pressRecongnizer release]; } cell.textLabel.font = [UIFont systemFontOfSize:10]; [[cell ignition] setImage:[UIImage imageNamed:@"ignition.png"]]; [[cell direction] setImage:[UIImage imageNamed:@"south.png"]]; cell.licPlate.text = cellValue; NSLog(@"cellvalue for cellforRow: %@", cell.licPlate.text); return cell; } 

在（void）tableCellPressed：（UILongPressGestureRecognizer *）识别器方法

 - (void)tableCellPressed:(UILongPressGestureRecognizer *)recognizer { VehicleListCell* cell = (VehicleListCell *)[recognizer view]; cellValueForLongPress = cell.licPlate.text; NSLog(@"cell value: %@", cellValueForLongPress); UIAlertView *alert = [[UIAlertView alloc] initWithTitle:nil message:nil delegate:self cancelButtonTitle:@"Cancel" otherButtonTitles: nil] ; [alert addButtonWithTitle:@"Add to Favourites"]; [alert addButtonWithTitle:@"Take to Map"]; [alert show]; } 

在警报视图方法中：

 -(void)alertView:(UIAlertView *)alert clickedButtonAtIndex:(NSInteger)buttonIndex { NSString *title = [alert buttonTitleAtIndex:buttonIndex]; NSManagedObjectContext *context = [app managedObjectContext]; Favouritesdata * favourites = [NSEntityDescription insertNewObjectForEntityForName:@"Favouritesdata" inManagedObjectContext:context]; if([title isEqualToString:@"Add to Favourites"]) { NSLog(@"Added to favourites."); NSLog(@"cellValueForLongPress: %@", cellValueForLongPress); if (cellValueForLongPress <= 0) { NSLog(@"There is no value to save"); } else { favourites.licenseplate = cellValueForLongPress; } [alert dismissWithClickedButtonIndex:0 animated:YES]; } else if([title isEqualToString:@"Take to Map"]) { NSLog(@"Go to MapView"); } NSError *error; if (![context save:&error]) { NSLog(@"Error Occured");} } 

可能是什么问题？

Answer 1

问题是你的长按手势识别器会触发每个状态，开始，结束等。如果事件的状态不是’开始’状态，那么你应该返回而不执行后续代码。

 - (void)tableCellPressed:(UILongPressGestureRecognizer *)recognizer { if (recognizer.state != UIGestureRecognizerStateBegan) { return; } // ... rest of code } 

Answer 2

它会多次触发以指示手势的不同状态（开始，更改，结束等）。 因此，在处理程序方法中，检查手势识别器的state属性，以避免在手势的每个状态下执行操作。

在你的情况下：

 - (void)tableCellPressed:(UILongPressGestureRecognizer *)recognizer { VehicleListCell* cell = (VehicleListCell *)[recognizer view]; cellValueForLongPress = cell.licPlate.text; NSLog(@"cell value: %@", cellValueForLongPress); if (gestureRecognizer.state == UIGestureRecognizerStateBegan) { UIAlertView *alert = [[UIAlertView alloc] initWithTitle:nil message:nil delegate:self cancelButtonTitle:@"Cancel" otherButtonTitles: nil] ; [alert addButtonWithTitle:@"Add to Favourites"]; [alert addButtonWithTitle:@"Take to Map"]; [alert show]; } }