How do you load custom UITableViewCells from Xib files?
The question is simple: How do you load custom UITableViewCell from Xib files? Doing so allows you to use Interface Builder to design your cells. The answer apparently is not simple due to memory managment issues. This thread mentions the issue and suggests a solution, but is pre NDA-release and lacks code. Here's a long thread that discusses the issue without providing a definitive answer.
Here's some code I've used:
static NSString *CellIdentifier = @"MyCellIdentifier";
MyCell *cell = (MyCell *)[tableView dequeueReusableCellWithIdentifier:CellIdentifier];
if (cell == nil) {
NSArray *nib = [[NSBundle mainBundle] loadNibNamed:CellIdentifier owner:self options:nil];
cell = (MyCell *)[nib objectAtIndex:0];
}
To use this code, create MyCell.m/.h, a new subclass of UITableViewCell and add IBOutlets for the components you want. Then create a new "Empty XIB" file. Open the Xib file in IB, add a UITableViewCell object, set its identifier to "MyCellIdentifier", and set its class to MyCell and add your components. Finally, connect the IBOutlets to the components. Note that we did not set the File's Owner in IB.
Other methods advocate setting the File's Owner and warn of memory leaks if the Xib is not loaded via an additional factory class. I tested the above under Instruments/Leaks and saw no memory leaks.
So what's the canonical way to load cells from Xibs? Do we set File's Owner? Do we need a factory? If so, what's the code for the factory look like? If there are multiple solutions, let's clarify the pros and cons of each of them...
Here are two methods which the original author states was recommended by an IB engineer.
See the actual post for more details. I prefer method #2 as it seems simpler.
Method #1:
- (UITableViewCell *)tableView:(UITableView *)tableView cellForRowAtIndexPath:(NSIndexPath *)indexPath {
UITableViewCell *cell = [tableView dequeueReusableCellWithIdentifier:@"BDCustomCell"];
if (cell == nil) {
// Create a temporary UIViewController to instantiate the custom cell.
UIViewController *temporaryController = [[UIViewController alloc] initWithNibName:@"BDCustomCell" bundle:nil];
// Grab a pointer to the custom cell.
cell = (BDCustomCell *)temporaryController.view;
[[cell retain] autorelease];
// Release the temporary UIViewController.
[temporaryController release];
}
return cell;
}
Method #2:
- (UITableViewCell *)tableView:(UITableView *)tableView cellForRowAtIndexPath:(NSIndexPath *)indexPath {
UITableViewCell *cell = [tableView dequeueReusableCellWithIdentifier:@"BDCustomCell"];
if (cell == nil) {
// Load the top-level objects from the custom cell XIB.
NSArray *topLevelObjects = [[NSBundle mainBundle] loadNibNamed:@"BDCustomCell" owner:self options:nil];
// Grab a pointer to the first object (presumably the custom cell, as that's all the XIB should contain).
cell = [topLevelObjects objectAtIndex:0];
}
return cell;
}
Update (2014): Method #2 is still valid but there is no documentation for it anymore. It used to be in the official docs but is now removed in favor of storyboards.
I posted a working example on Github:
https://github.com/bentford/NibTableCellExample
正确的解决方案是这样的：
- (void)viewDidLoad
{
[super viewDidLoad];
UINib *nib = [UINib nibWithNibName:@"ItemCell" bundle:nil];
[[self tableView] registerNib:nib forCellReuseIdentifier:@"ItemCell"];
}
-(UITableViewCell *)tableView:(UITableView *)tableView cellForRowAtIndexPath:(NSIndexPath *)indexPath
{
// Create an instance of ItemCell
PointsItemCell *cell = [tableView dequeueReusableCellWithIdentifier:@"ItemCell"];
return cell;
}
Register
After iOS 7, this process has been simplified down to ( swift 3.0 ):
// For registering nib files
tableView.register(UINib(nibName: "MyCell", bundle: Bundle.main), forCellReuseIdentifier: "cell")
// For registering classes
tableView.register(MyCellClass.self, forCellReuseIdentifier: "cell")
( Note ) This is also achievable by creating the cells in the .xib or .stroyboard files, as prototype cells. If you need to attach a class to them, you can select the cell prototype and add the corresponding class (must be a descendant of UITableViewCell , of course).
Dequeue
And later on, dequeued using ( swift 3.0 ):
override func tableView(tableView: UITableView, cellForRowAtIndexPath indexPath: NSIndexPath) -> UITableViewCell
{
let cell : UITableViewCell = tableView.dequeueReusableCell(withIdentifier: "cell", for: indexPath)
cell.textLabel?.text = "Hello"
return cell
}
The difference being that this new method not only dequeues the cell, it also creates if non-existant (that means that you don't have to do if (cell == nil) shenanigans), and the cell is ready to use just as in the example above.
( Warning ) tableView.dequeueReusableCell(withIdentifier:for:) has the new behavior, if you call the other one (without indexPath: ) you get the old behavior, in which you need to check for nil and instance it yourself, notice the UITableViewCell? return value.
if let cell = tableView.dequeueReusableCell(withIdentifier: "cell", for: indexPath) as? MyCellClass
{
// Cell be casted properly
cell.myCustomProperty = true
}
else
{
// Wrong type? Wrong identifier?
}
And of course, the type of the associated class of the cell is the one you defined in the .xib file for the UITableViewCell subclass, or alternatively, using the other register method.
Configuration
Ideally, your cells have been already configured in terms of appearance and content positioning (like labels and image views) by the time you registered them, and on the cellForRowAtIndexPath method you simply fill them in.
All together
class MyCell : UITableViewCell
{
// Can be either created manually, or loaded from a nib with prototypes
@IBOutlet weak var labelSomething : UILabel? = nil
}
class MasterViewController: UITableViewController
{
var data = ["Hello", "World", "Kinda", "Cliche", "Though"]
// Register
override func viewDidLoad()
{
super.viewDidLoad()
tableView.register(MyCell.self, forCellReuseIdentifier: "mycell")
// or the nib alternative
}
override func tableView(tableView: UITableView, numberOfRowsInSection section: Int) -> Int
{
return data.count
}
// Dequeue
override func tableView(tableView: UITableView, cellForRowAtIndexPath indexPath: NSIndexPath) -> UITableViewCell
{
let cell = tableView.dequeueReusableCell(withIdentifier: "mycell", for: indexPath) as! MyCell
cell.labelSomething?.text = data[indexPath.row]
return cell
}
}
And of course, this is all available in ObjC with the same names.
链接地址: http://www.djcxy.com/p/78228.html