Subclassing UITableViewCell（15）

注意属性都是weak

// Load the NIB file
UINib *nib = [UINib nibWithNibName:@"HomepwnerItemCell" bundle:nil];

// Register this NIB which contains the cell

[[self tableView] registerNib:nib  forCellReuseIdentifier:@"HomepwnerItemCell"]; 

// Get the new or recycled cell

HomepwnerItemCell *cell = [tableView  dequeueReusableCellWithIdentifier:@"HomepwnerItemCell"]; 

xib与nib之间的关系

Let’s go back to the UINib class you used when loading HomepwnerItemCell.xib. An instance of UINib knows how to read a XIB file. (Remember, XIB and NIB are used interchangeably; technically, an application loads NIBs, but we work with XIBs, so it’s easier to call them that.)

An instance of UINib is created with the contents of a XIB file. It loads the data in that file and holds on to it as long as it lives. When it is sent the message instantiateWithOwner:options:, the UINib parses that data: all of the archived objects come alive, and all of the connections are established. (The object passed as the first argument is the File's Owner.)

In Chapter 10, you loaded a XIB file by sending the message loadNibNamed:owner:options: to the main NSBundle without ever using UINib. Well, loadNibNamed:owner:options: uses UINib under the hood. It creates an instance of UINib and sends it the message instantiateWithOwner:options:, relaying the options and owner arguments.

Both of these methods return an NSArray. This array contains all of the top-level objects in the XIB file (the ones that aren’t under a disclosure tab in the outline view of the XIB). When you register a XIB file with a table view, it scans this array for an instance of UITableViewCell or a subclass of it and returns it to your data source.

Since the table view just scans the XIB file for a UITableViewCell, it is important that you only put one instance of UITableViewCell in a XIB file used for this purpose. Otherwise, the table view will get confused and throw an exception.