Empty UITableView not bouncing when loaded from a nib

问题

A UITableView should bounce (even when empty) when user scrolls as long as the bounces and alwaysBounceVertical properties are set to YES. When I initialize a UITableViewController, everything works as expected. When I initialized a UIViewController loaded from a nib with a simple view hierarchy: a top level UIView with a single UITableView child, then the table view doesn't bounce anymore. Here is the code I used:

#import <UIKit/UIKit.h>

@interface AppDelegate : UIResponder <UIApplicationDelegate, UITableViewDataSource>
@end

@implementation AppDelegate

@synthesize window = _window;

- (BOOL) application:(UIApplication *)application didFinishLaunchingWithOptions:(NSDictionary *)launchOptions
{
    self.window = [[UIWindow alloc] initWithFrame:[[UIScreen mainScreen] bounds]];

    UIViewController *rootViewController = nil;
    UITableView *tableView;
    BOOL loadFromNib = NO;
    if (loadFromNib)
    {
        rootViewController = [[UIViewController alloc] initWithNibName:@"ViewController" bundle:nil];
        tableView = [rootViewController.view.subviews objectAtIndex:0];
    }
    else
    {
        rootViewController = [[UITableViewController alloc] initWithStyle:UITableViewStylePlain];
        tableView = (UITableView *)rootViewController.view;
    }
    tableView.dataSource = self;
    NSLog(@"%@ bounces: %@", tableView.class, tableView.bounces ? @"YES" : @"NO");
    NSLog(@"%@ alwaysBounceVertical: %@", tableView.class, tableView.alwaysBounceVertical ? @"YES" : @"NO");

    self.window.rootViewController = rootViewController;
    [self.window makeKeyAndVisible];

    return YES;
}

- (NSInteger) tableView:(UITableView *)tableView numberOfRowsInSection:(NSInteger)section
{
    return 0;
}

- (UITableViewCell *) tableView:(UITableView *)tableView cellForRowAtIndexPath:(NSIndexPath *)indexPath
{
    return [[UITableViewCell alloc] initWithStyle:UITableViewCellStyleDefault reuseIdentifier:nil];
}

@end

When I run this code with the loadFromNib variable set to YES or NO, it always logs this:

UITableView bounces: YES
UITableView alwaysBounceVertical: YES

But when I load it from the nib (i.e. loadFromNib is set to YES), the table view doesn’t bounce when I try to scroll. Why doesn’t it bounce?

回答1:

I cannot precisely explain why, but the behaviour with empty table views seems pretty erratic. Anyway, setting tableView.bounces = YES manually (e.g. in the -viewDidLoad method of the view controller the table view belongs to) fixes such issues and ensures that your table view always bounces, even when empty.

来源：https://stackoverflow.com/questions/12316055/empty-uitableview-not-bouncing-when-loaded-from-a-nib

标签

ios

uitableview