Set UITableView Delegate and DataSource

问题:

This is my problem: I have this small UITableView in my storyboard:

And this is my code:

SmallTableViewController.h

#import <UIKit/UIKit.h>
#import "SmallTable.h"

@interface SmallViewController : UIViewController

@property (weak, nonatomic) IBOutlet UITableView *myTable;

@end

SmallTableViewController.m

#import "SmallViewController.h"

@interface SmallViewController ()

@end

@implementation SmallViewController
@synthesize myTable = _myTable;

- (void)viewDidLoad
{
    SmallTable *myTableDelegate = [[SmallTable alloc] init];
    [super viewDidLoad];
    [self.myTable setDelegate:myTableDelegate];
    [self.myTable setDataSource:myTableDelegate];

    // Do any additional setup after loading the view, typically from a nib.
}

- (void)viewDidUnload
{
    [super viewDidUnload];
    // Release any retained subviews of the main view.
}

- (BOOL)shouldAutorotateToInterfaceOrientation:(UIInterfaceOrientation)interfaceOrientation
{
    return (interfaceOrientation != UIInterfaceOrientationPortraitUpsideDown);
}

@end

Now as you can see, I want to set an instance called myTableDelegate as Delegate and DataSource of myTable.

This is the Source of SmallTable class.

SmallTable.h

#import <Foundation/Foundation.h>

@interface SmallTable : NSObject <UITableViewDelegate , UITableViewDataSource>

@end

SmallTable.m

@implementation SmallTable

- (NSInteger)numberOfSectionsInTableView:(UITableView *)tableView
{
    // Return the number of sections.
    return 0;
}

- (NSInteger)tableView:(UITableView *)tableView numberOfRowsInSection:(NSInteger)section
{
    // Return the number of rows in the section.
    return 5;
}

- (UITableViewCell *)tableView:(UITableView *)tableView cellForRowAtIndexPath:(NSIndexPath *)indexPath
{
    static NSString *CellIdentifier = @"Cell";
    UITableViewCell *cell = [tableView dequeueReusableCellWithIdentifier:CellIdentifier];

    // Configure the cell...
    cell.textLabel.text = @"Hello there!";

    return cell;
}

#pragma mark - Table view delegate

- (void)tableView:(UITableView *)tableView didSelectRowAtIndexPath:(NSIndexPath *)indexPath
{
    NSLog(@"Row pressed!!");
}

@end

I implemented all the UITableViewDelegate and UITableViewDataSource method that the app need. Why it just crash before the view appear??

Thanks!!

回答1:

rickster is right. But I guess you need to use a strong qualifier for your property since at the end of your viewDidLoad method the object will be deallocated anyway.

@property (strong,nonatomic) SmallTable *delegate;

// inside viewDidload

[super viewDidLoad];
self.delegate = [[SmallTable alloc] init];    
[self.myTable setDelegate:myTableDelegate];
[self.myTable setDataSource:myTableDelegate];

But is there any reason to use a separated object (data source and delegate) for your table? Why don't you set SmallViewController as both the source and the delegate for your table?

In addition you are not creating the cell in the correct way. These lines do nothing:

static NSString *CellIdentifier = @"Cell";
UITableViewCell *cell = [tableView dequeueReusableCellWithIdentifier:CellIdentifier];

// Configure the cell...
cell.textLabel.text = @"Hello there!";

dequeueReusableCellWithIdentifier simply retrieves from the table "cache" a cell that has already created and that can be reused (this to avoid memory consumption) but you haven't created any.

Where are you doing alloc-init? Do this instead:

static NSString *CellIdentifier = @"Cell";
UITableViewCell *cell = [tableView dequeueReusableCellWithIdentifier:CellIdentifier];
if(!cell) {
    cell = // alloc-init here
}
// Configure the cell...
cell.textLabel.text = @"Hello there!";

Furthermore say to numberOfSectionsInTableView to return 1 instead of 0:

- (NSInteger)numberOfSectionsInTableView:(UITableView *)tableView
{
    // Return the number of sections.
    return 1;
}

回答2:

Presumably you're using ARC? Your myTableDelegate is only referenced in a local variable in viewDidLoad -- once that method ends, it's deallocated. (In the delegate/datasource pattern, objects do not own their delegates, so the table view's references back to your object are weak.) I wouldn't expect that alone to cause a crash, but it's likely key to your problem.

回答3:

setDelegate will not retain the delegate.

And

numberOfSectionsInTableView method has to return 1 instead of 0;

回答4:

(NSInteger)numberOfSectionsInTableView:(UITableView *)tableView
{
    // Return the number of sections.
    return 0;
}

Number of sections should be set at least one

回答5:

The delegate of an UITableView object must adopt the UITableViewDelegate protocol. Optional methods of the protocol allow the delegate to manage selections, configure section headings and footers, help to delete methods.