UIimage View

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UIImageView 的contentMode这个属性是用来设置图片的显示方式，如居中、居右，是否缩放等，有以下几个常量可供设定：
UIViewContentModeScaleToFill
UIViewContentModeScaleAspectFit
UIViewContentModeScaleAspectFill
UIViewContentModeRedraw
UIViewContentModeCenter
UIViewContentModeTop
UIViewContentModeBottom
UIViewContentModeLeft
UIViewContentModeRight
UIViewContentModeTopLeft
UIViewContentModeTopRight
UIViewContentModeBottomLeft
UIViewContentModeBottomRight
注意以上几个常量，凡是没有带Scale的，当图片尺寸超过 ImageView尺寸时，只有部分显示在ImageView中。UIViewContentModeScaleToFill属性会导致图片变形。UIViewContentModeScaleAspectFit会保证图片比例不变，而且全部显示在ImageView中，这意味着ImageView会有部分空白。UIViewContentModeScaleAspectFill也会证图片比例不变，但是是填充整个ImageView的，可能只有部分图片显示出来。

比较字符串用isEqualToString
计时器销毁invalidate
progressView和activityIndictor控制图片的加载显示图的加载进度，加载过程中

- (void)viewDidLoad {
    [super viewDidLoad];
    // Do any additional setup after loading the view, typically from a nib.
    //初始化imageview并分配空间
    self.imageview =[[UIImageView alloc]initWithFrame:CGRectMake(30, 160, 260, 180)];
    //设置imageview的背景色
    self.imageview.backgroundColor=[UIColor groupTableViewBackgroundColor];
    //在imageview上贴上图片
    [self.imageview setImage:[UIImage imageNamed:@"222.jpg"]];
    //设置imagevie的默认显示模式
    self.imageview.contentMode=UIViewContentModeScaleAspectFit;
    //将view贴到viewcontrol上
    [self.view addSubview:self.imageview];
    
    //定义在segment上显示的数组
    NSArray *arrar=[[NSArray alloc]initWithObjects:@"111.png",@"222.jpg", nil];
    //初始化
    self.segment=[[UISegmentedControl alloc]initWithItems:arrar];
    //设置segmentcontrol的frame
    self.segment.frame=CGRectMake(30, 460, 260, 30);
    //添加回调
    [self.segment addTarget:self action:@selector(tapB:) forControlEvents:UIControlEventValueChanged];
    //默认按键
    self.segment.selectedSegmentIndex=0;
    [self.view addSubview:self.segment];
  /*
    self.label=[[UILabel alloc]initWithFrame:CGRectMake(100, 150, 100, 50)];
    self.label.backgroundColor=[UIColor groupTableViewBackgroundColor];
    self.label.text=@"显示一段文字";
    
    [self.view addSubview:self.label];
    
    self.button=[[UIButton alloc]initWithFrame:CGRectMake(100, 250,100 ,50 )];;
    self.button.backgroundColor=[UIColor groupTableViewBackgroundColor];
    [self.button addTarget:self action:@selector(tapA) forControlEvents:UIControlEventTouchUpInside];
    _isButton=YES;
    [self.button setTitle:@"按钮" forState: UIControlStateNormal];
    [self.view addSubview:self.button];*/
}
/*
-(void)tapA
{
    if (_isButton==YES) {
        self.label.text=@"你好";
        [self.view addSubview:self.label];
    } else {
        self.label.text=@"欢迎";
        [self.view addSubview:self.label];
    }
}*/
-(void)tapB:(UISegmentedControl *)sender
{
    switch (sender.selectedSegmentIndex) {
        case 1:
            [self.imageview setImage:[UIImage imageNamed:@"111.png"]];
            break;
        case 0:
            [self.imageview setImage:[UIImage imageNamed:@"222.jpg"]];
            break;
            
        default:
            break;
    }
}



- (void)viewDidLoad {
    [super viewDidLoad];
    // Do any additional setup after loading the view, typically from a nib.
 /*   //初始化imageview并分配空间
    self.imageview =[[UIImageView alloc]initWithFrame:CGRectMake(30, 160, 260, 180)];
    //设置imageview的背景色
    self.imageview.backgroundColor=[UIColor groupTableViewBackgroundColor];
    //在imageview上贴上图片
    [self.imageview setImage:[UIImage imageNamed:@"222.jpg"]];
    //设置imagevie的默认显示模式
    self.imageview.contentMode=UIViewContentModeScaleAspectFit;
    //将view贴到viewcontrol上
    [self.view addSubview:self.imageview];
    
    //定义在segment上显示的数组
    NSArray *arrar=[[NSArray alloc]initWithObjects:@"111.png",@"222.jpg", nil];
    //初始化
    self.segment=[[UISegmentedControl alloc]initWithItems:arrar];
    //设置segmentcontrol的frame
    self.segment.frame=CGRectMake(30, 460, 260, 30);
    //添加回调
    [self.segment addTarget:self action:@selector(tapB:) forControlEvents:UIControlEventValueChanged];
    //默认按键
    self.segment.selectedSegmentIndex=0;
    [self.view addSubview:self.segment];
  */
 
    self.label=[[UILabel alloc]initWithFrame:CGRectMake(100, 150, 100, 50)];
    self.label.backgroundColor=[UIColor groupTableViewBackgroundColor];
    self.label.text=@"显示一段文字";
    
    [self.view addSubview:self.label];
    
    self.button=[[UIButton alloc]initWithFrame:CGRectMake(100, 250,100 ,50 )];;
    self.button.backgroundColor=[UIColor groupTableViewBackgroundColor];
    [self.button addTarget:self action:@selector(tapA) forControlEvents:UIControlEventTouchUpInside];
    _isButton=YES;
    [self.button setTitle:@"按钮" forState: UIControlStateNormal];
    [self.view addSubview:self.button];
}

-(void)tapA
{
    if (_isButton==YES) {
        self.label.text=@"你好";
        [self.view addSubview:self.label];
    } else {
        self.label.text=@"欢迎";
        [self.view addSubview:self.label];
    }
}

UIimage View

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原文地址：http://www.cnblogs.com/quwujin/p/4770679.html