ios - 純代碼創建collectionView

• 開始考慮好一點點時間,因為一般的都是用xib,或者storyboard來寫的.這次用純代碼...廢話較多請看

• 首先把storyboard干掉,工程里面的main干掉
  

• 由於干掉了storyboard則啟動的控制器要在Appdelegate中指定

#import "AppDelegate.h"
#import "ViewController.h"
@interface AppDelegate ()

@end

@implementation AppDelegate


- (BOOL)application:(UIApplication *)application didFinishLaunchingWithOptions:(NSDictionary *)launchOptions {

    self.window = [[UIWindow alloc] initWithFrame:[UIScreen mainScreen].bounds];
    UICollectionViewFlowLayout * fly = [UICollectionViewFlowLayout new];
    fly.itemSize = CGSizeMake(50, 50);
    fly.sectionInset = UIEdgeInsetsMake(50, 10, 0, 10);
    //創建collectionViewController並設置布局參數
    ViewController * vc = [[ViewController alloc] init];
    self.window.rootViewController = vc;
    UICollectionView * colView = [[UICollectionView alloc] initWithFrame:[UIScreen mainScreen].bounds collectionViewLayout:fly];
    vc.collectionView = colView;
    //必須注冊可重用id
    [vc.collectionView registerClass:[UICollectionViewCell class] forCellWithReuseIdentifier:@"Cell"];
    [vc.collectionView setCollectionViewLayout:fly];
    vc.collectionView.backgroundColor = [UIColor blueColor];
    [self.window makeKeyAndVisible];
    return YES;
    
}

• 上述代碼中,一定要在創建viewcontroller的時候給它的collectionView指定布局參數,否則一直會報錯,報錯原因就是:"請給UICollectionView初始化一個non-nil的layout(布局參數)",如果報這個錯誤而你在控制的.m文件中viewDidload中給self.CollectionView 設置並且初始化了一個布局參數,再次運行程序依然會報上面的錯誤.
• 所以創建控制器的時候給控制器.collectionView指定布局參數.
• 指定布局參數后還會報錯,說:請給cell設置一個可重用ID,當你在viewdidload中注冊了一個Id后依然報錯,打全局斷點會崩到數據源第三個方法中...此時正確的解決方式就是,在Appdelegate中創建控制器的時候讓控制器的.collectionView register 注冊一個可重用id.此時再運行正確.
• 注意點1: 此時打斷點在Viewcontroller中的viewdidload方法,----結果是根本不會執行viewdidload,所以它才報錯讓你注冊一個可重用id,如果在Appdelegate中的控制器的.collectionView注冊一個可重用ID則 解決.

#import "ViewController.h"

@interface ViewController ()<UICollectionViewDataSource,UICollectionViewDelegate,UICollectionViewDelegateFlowLayout>


/** 布局參數 */ 
//@property (nonatomic, strong) UICollectionViewFlowLayout *flowLayout;

@end

@implementation ViewController

//此時懶加載沒有用 因為viewdidload中的方法根本不會執行
//-(UICollectionViewFlowLayout *)flowLayout{
//
//    if (_flowLayout == nil) {
//        _flowLayout = [[UICollectionViewFlowLayout alloc] init];
//    }
//    return _flowLayout;
//}


//不執行---
- (void)viewDidLoad {
    [super viewDidLoad];
    
//    self.view.backgroundColor = [UIColor whiteColor];
//    self.collectionView.dataSource = self;
//    self.collectionView.delegate = self;
//    [self.collectionView registerClass:[UICollectionViewCell class] forCellWithReuseIdentifier:@"Cell"];
}

-(void)collectionView:(UICollectionView *)collectionView didSelectItemAtIndexPath:(NSIndexPath *)indexPath{

    NSLog(@"dianji");
}

- (void)didReceiveMemoryWarning {
    [super didReceiveMemoryWarning];
    // Dispose of any resources that can be recreated.
}


#pragma mark <UICollectionViewDataSource>


- (NSInteger)collectionView:(UICollectionView *)collectionView numberOfItemsInSection:(NSInteger)section {
    return 100;
}

- (UICollectionViewCell *)collectionView:(UICollectionView *)collectionView cellForItemAtIndexPath:(NSIndexPath *)indexPath {
    static NSString * const reuseIdentifier = @"Cell";
    UICollectionViewCell * cell = [collectionView dequeueReusableCellWithReuseIdentifier:reuseIdentifier forIndexPath:indexPath];
    cell.backgroundColor = [UIColor colorWithPatternImage:[UIImage imageNamed:@"Snip20160422_5"]];
    return cell;
}



@end

綜上: 純 代碼創建collectionView,以及collectionVIewController,在哪里創建的collectionViewcontroller就在哪里設置布局參數以及cell的可重用ID即可. 切記切記...demo地址:http://pan.baidu.com/s/1i4KLlbv