How to get notified of UITableViewCell move start

问题:

I have a UITableView in my iOS app that gets refreshed periodically. The user is also able to move the tableview rows at all times (the tableview is always in editing mode).

I want to stop the refresh timer when the user starts dragging a row and start it again when the row is dropped.

The last part should be easy with moveRowAtIndexPath, but how to get notified about drag start?

Thanks!

回答1:

Your UITableViewDelegate will receive the following notifications in response to reordering actions:

- (void)tableView:(UITableView *)tableView willBeginReorderingRowAtIndexPath:(NSIndexPath *)indexPath;
- (void)tableView:(UITableView *)tableView didEndReorderingRowAtIndexPath:(NSIndexPath *)indexPath;
- (void)tableView:(UITableView *)tableView didCancelReorderingRowAtIndexPath:(NSIndexPath *)indexPath;

回答2:

I ran into the same problem some time ago and didn't find a solution. While I started this answer with an explanation why it can't be done, I actually found out how it can be done! :-)

In short: You have to create a custom subclass of UITableViewCell. Override layoutSubviews to attach a UILongPressGestureRecognizer to UITableViewCellReorderControl. Define a protocol and use a delegate to inform whoever you want to about the dragging state.

CustomTableViewCell.h:

#import <UIKit/UIKit.h>

@protocol CustomTableViewCellDelegate;

@interface CustomTableViewCell : UITableViewCell {
}

@property (nonatomic, assign) id <CustomTableViewCellDelegate> delegate;

@end

@protocol CustomTableViewCellDelegate
- (void)CustomTableViewCell:(CustomTableViewCell *)cell isDragging:(BOOL)value;
@end

CustomTableViewCell.m:

#import "CustomTableViewCell.h"

@implementation CustomTableViewCell

@synthesize delegate = _delegate;

- (void)handleGesture:(UIGestureRecognizer *)gestureRecognizer {
    if (gestureRecognizer.state == UIGestureRecognizerStateBegan) {
        [_delegate CustomTableViewCell:self isDragging:YES];    // Dragging started
    } else if (gestureRecognizer.state == UIGestureRecognizerStateEnded) {
        [_delegate CustomTableViewCell:self isDragging:NO];     // Dragging ended
    }
}

- (void)layoutSubviews {
    [super layoutSubviews];

    for (UIView *view in self.subviews) {
        if ([NSStringFromClass ([view class]) rangeOfString:@"ReorderControl"].location != NSNotFound) {    // UITableViewCellReorderControl
            if (view.gestureRecognizers.count == 0) {
                UILongPressGestureRecognizer *gesture = [[UILongPressGestureRecognizer alloc] initWithTarget:self action:@selector(handleGesture:)];
                gesture.cancelsTouchesInView    = NO;
                gesture.minimumPressDuration    = 0.150;
                [view addGestureRecognizer:gesture];
            }
        }
    }
}

@end

Be aware that while this code doesn't use any private APIs it still might stop working if Apple changes its internal implementation (i.e. by changing the classname of UITableViewCellReorderControl).

回答3:

Just I found a hack, since apple will reduce the alpha, we can use that i guess

@interface CustomTableViewCell () 
@property (nonatomic, assign) BOOL isDragging;
@end

-(void)draggingWillBegan
{
    //use a delegate method to inform tableview
}

-(void)draggingDidEnd
{
    //use a delegate method to inform tableview
}

- (void)layoutSubviews
{
    [super layoutSubviews];

    //Since apple wont provide en
    if(self.alpha <= 0.95 && !self.isDragging){
        self.isDragging = YES;
        [self draggingWillBegan];
    }

    if(self.alpha >= 0.95 && self.isDragging){
        self.isDragging = NO;
        [self draggingDidEnd];
    }
}

回答4:

this method gets called when you're done moving cells:

- (void) tableView:(UITableView *)tableView moveRowAtIndexPath:(NSIndexPath *)sourceIndexPath toIndexPath:(NSIndexPath *)destinationIndexPath