懶加載 ?也稱為延遲加載
即在需要的時候才加載（效率低，占用內(nèi)存欣μ健）
所謂懶加載然爆，寫的是其get方法.
注意：如果是懶加載的話則一定要注意先判斷是否已經(jīng)有了，如果沒有那么再去進(jìn)行實例化
使用懶加載的好處：
（1）不必將創(chuàng)建對象的代碼全部寫在viewDidLoad方法中黍图，代碼的可讀性更強(qiáng)
（2）每個控件的getter方法中分別負(fù)責(zé)各自的實例化處理曾雕，代碼彼此之間的獨立性強(qiáng)，松耦合
?#import "YYViewController.h"
?#define POTOIMGW? ? 200
?#define POTOIMGH? ? 300
?#define POTOIMGX? ? 60
#define? POTOIMGY? ? 50
?@interface YYViewController ()
?@property(nonatomic,strong)UILabel *firstlab;
?@property(nonatomic,strong)UILabel *lastlab;
@property(nonatomic,strong)UIImageView *icon;
@property(nonatomic,strong)UIButton *leftbtn;
@property(nonatomic,strong)UIButton *rightbtn;
@property(nonatomic,strong)NSArray *array;
@property(nonatomic ,assign)int i;
-(void)change;
?@end
?@implementation YYViewController
?- (void)viewDidLoad
?{? ? ?[super viewDidLoad];
? ? ?[self change];
?}
-(void)change
?{
? ? [self.firstlab setText:[NSString stringWithFormat:@"%d/5",self.i+1]];
? ?//先get再set
? ?self.icon.image=[UIImage imageNamed:self.array[self.i][@"name"]];
? ? ?self.lastlab.text=self.array[self.i][@"desc"];
? ? ?self.leftbtn.enabled=(self.i!=0);
? ? self.rightbtn.enabled=(self.i!=4); }
?//延遲加載
?/**1.圖片的序號標(biāo)簽*/
-(UILabel *)firstlab
?{
? ? //判斷是否已經(jīng)有了助被，若沒有剖张，則進(jìn)行實例化
? ? ?if (!_firstlab) {
? ? ? ?_firstlab=[[UILabel alloc]initWithFrame:CGRectMake(20, 10, 300, 30)];
? ? ? ? ?[_firstlab setTextAlignment:NSTextAlignmentCenter];
? ? ? ? ?[self.view addSubview:_firstlab];
? ? ?}
? ? ?return _firstlab;
?}
?/**2.圖片控件的延遲加載*/
?-(UIImageView *)icon
?{
? ? ? //判斷是否已經(jīng)有了，若沒有揩环，則進(jìn)行實例化
? ? ?if (!_icon) {
? ? ? ?_icon=[[UIImageView alloc]initWithFrame:CGRectMake(POTOIMGX, POTOIMGY, POTOIMGW, POTOIMGH)];
? ? ? ? ?UIImage *image=[UIImage imageNamed:@"biaoqingdi"];
? ? ? ? _icon.image=image;
? ? ? ? ?[self.view addSubview:_icon];
? ? }
? ? return _icon;
?}
?/**3.描述控件的延遲加載*/
?-(UILabel *)lastlab
?{
? ?? //判斷是否已經(jīng)有了搔弄，若沒有，則進(jìn)行實例化
? ? ?if (!_lastlab) {
? ? ? ? ?_lastlab=[[UILabel alloc]initWithFrame:CGRectMake(20, 400, 300, 30)];
? ? ? ?[_lastlab setTextAlignment:NSTextAlignmentCenter];
? ? ? ? [self.view addSubview:_lastlab];
? ? ?}
? ? return _lastlab;
?}
?/**4.左鍵按鈕的延遲加載*/
?-(UIButton *)leftbtn
?{
? ? ? //判斷是否已經(jīng)有了丰滑，若沒有顾犹，則進(jìn)行實例化
? ? ?if (!_leftbtn) {
? ? ? ? _leftbtn=[UIButton buttonWithType:UIButtonTypeCustom];
? ? ? ? ?_leftbtn.frame=CGRectMake(0, self.view.center.y, 40, 40);
? ? ? ? ?[_leftbtn setBackgroundImage:[UIImage imageNamed:@"left_normal"] forState:UIControlStateNormal];
? ? ? ? ?[_leftbtn setBackgroundImage:[UIImage imageNamed:@"left_highlighted"] forState:UIControlStateHighlighted];
? ? ? ? ?[self.view addSubview:_leftbtn];
? ? ? ? ?[_leftbtn addTarget:self action:@selector(leftclick:) forControlEvents:UIControlEventTouchUpInside];
? ? }
? ? return _leftbtn;
?}
/**5.右鍵按鈕的延遲加載*/
-(UIButton *)rightbtn
?{
? ? ?if (!_rightbtn) {
? ? ? ? _rightbtn=[UIButton buttonWithType:UIButtonTypeCustom];
? ? ? ? ?_rightbtn.frame=CGRectMake(POTOIMGX+POTOIMGW+10, self.view.center.y, 40, 40);
? ? ? ? [_rightbtn setBackgroundImage:[UIImage imageNamed:@"right_normal"] forState:UIControlStateNormal];
? ? ? ? ?[_rightbtn setBackgroundImage:[UIImage imageNamed:@"right_highlighted"] forState:UIControlStateHighlighted];
? ? ? ? ?[self.view addSubview:_rightbtn];
? ? ? ? [_rightbtn addTarget:self action:@selector(rightclick:) forControlEvents:UIControlEventTouchUpInside];
? ? ?}
? ? ?return _rightbtn;
?}
?//array的get方法
?-(NSArray *)array
?{
? ?if (_array==nil) {
? ? ? NSString *path=[[NSBundle mainBundle] pathForResource:@"data" ofType:@"plist"];
? ? ? ? ?_array=[[NSArray alloc]initWithContentsOfFile:path];
? ? ?}
? ? return _array;
}
?-(void)rightclick:(UIButton *)btn
?{
? ? ?self.i++;
? ? ?[self change];
}
-(void)leftclick:(UIButton *)btn
{
? ? self.i--;
? ? ?[self change];
?}
@end
