Touch and pull down a view

Question

I have a uiview at the top of the interface (below the status bar) that only the bottom part of it is shown.

Actually, I want to make the red uiview to slide down

Answer 1

No needs to find a workaround of drag-n-drop. An UIScrollView can do it without any performance loss brought by listening on touches.

@interface PulldownView : UIScrollView

@end

@implementation PulldownView

- (id)initWithFrame:(CGRect)frame
{
    self = [super initWithFrame:frame];
    if (!self) {
        return self;
    }
    self.pagingEnabled = YES;
    self.bounces = NO;
    self.showsVerticalScrollIndicator = NO;
    [self setBackgroundColor:[UIColor clearColor]];
    double pixelsOutside = 20;// How many pixels left outside.
    self.contentSize = CGSizeMake(320, frame.size.height * 2 - pixelsOutside);
    // redArea is the draggable area in red.
    UIView *redArea = [[UIView alloc] initWithFrame:frame];
    redArea.backgroundColor = [UIColor redColor];
    [self addSubview:redArea];
    return self;
}

// What this method does is to make sure that the user can only drag the view from inside the area in red.
- (UIView *)hitTest:(CGPoint)point withEvent:(UIEvent *)event
{
    if (point.y > height)
    {
        // Leaving useless touches to the views under it.
        return nil;
    }
    return [super hitTest:point withEvent:event];
}

@end

How to use:
1. Initialize an instance of PulldownView.
2. Add any content you want to display to the instance using [addSubview:].
3. Hide the area in red.

[pulldownView setContentOffset:CGPointMake(0, heightOfTheView - pixelsOutside)];

This is a simple example. You can add any features to it like adding a titled button bar on the bottom of the draggable area to implement click-n-drop, or adding some method to the interface to reposition it by the caller.