iOS开发之-Table View-Managing the Reordering of Rows-优快云博客

本文详细介绍了如何在表格视图中管理行的重新排列过程，包括行被拖动时的行为、接受新位置的判断及数据模型更新的实现。

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Managing the Reordering of Rows

What Happens When a Row is Relocated

1. The delegate assigns the controls in tableView:cellForRowAtIndexPath: by setting the showsReorderControl property of UITableViewCell objects to YES.

When the table view receives the setEditing:animated: message, it resends the same message to the cell objects corresponding to its visible rows. After that, the sequence of messages is as follows:

Every time the dragged row is over a destination, the table view sends tableView:targetIndexPathForMoveFromRowAtIndexPath:toProposedIndexPath: to its delegate (if it implements the method). In this method the delegate may reject the current destination for the dragged row and specify an alternative one.
The table view sends tableView:moveRowAtIndexPath:toIndexPath: to its data source (if it implements the method). In this method the data source updates the data-model array that is the source of items for the table view, moving the item to a different location in the array.

Examples of Moving a Row

Listing 8-1  Excluding a row from relocation
- (BOOL)tableView:(UITableView *)tableView canMoveRowAtIndexPath:(NSIndexPath *)indexPath {
    if (indexPath.row == 0) // Don't move the first row
      return NO;
 
   return YES;
}

Listing 8-2  Updating the data-model array for the relocated row
- (void)tableView:(UITableView *)tableView moveRowAtIndexPath:(NSIndexPath *)sourceIndexPath toIndexPath:(NSIndexPath *)destinationIndexPath {
    NSString *stringToMove = [[self.reorderingRows objectAtIndex:sourceIndexPath.row] retain];
    [self.reorderingRows removeObjectAtIndex:sourceIndexPath.row];
    [self.reorderingRows insertObject:stringToMove atIndex:destinationIndexPath.row];
    [stringToMove release];
}

Listing 8-3  Retargeting the destination row of a move operation
- (NSIndexPath *)tableView:(UITableView *)tableView
        targetIndexPathForMoveFromRowAtIndexPath:(NSIndexPath *)sourceIndexPath
        toProposedIndexPath:(NSIndexPath *)proposedDestinationIndexPath {
    NSDictionary *section = [data objectAtIndex:sourceIndexPath.section];
    NSUInteger sectionCount = [[section valueForKey:@"content"] count];
    if (sourceIndexPath.section != proposedDestinationIndexPath.section) {
        NSUInteger rowInSourceSection =
             (sourceIndexPath.section > proposedDestinationIndexPath.section) ?
               0 : sectionCount - 1;
        return [NSIndexPath indexPathForRow:rowInSourceSection inSection:sourceIndexPath.section];
    } else if (proposedDestinationIndexPath.row >= sectionCount) {
        return [NSIndexPath indexPathForRow:sectionCount - 1 inSection:sourceIndexPath.section];
    }
    // Allow the proposed destination.
    return proposedDestinationIndexPath;
}