IOS 中的一些知识点

16.状态栏的网络活动风火轮是否旋转：

[UIApplication sharedApplication].networkActivityIndicatorVisible，默认值是NO。

17.截取屏幕图片：

//创建一个基于位图的图形上下文并指定大小为CGSizeMake(200,400)

UIGraphicsBeginImageContext(CGSizeMake(200,400));

//renderInContext 呈现接受者及其子范围到指定的上下文

[self.view.layer renderInContext:UIGraphicsGetCurrentContext()];

//返回一个基于当前图形上下文的图片

UIImage *aImage = UIGraphicsGetImageFromCurrentImageContext();

//移除栈顶的基于当前位图的图形上下文

UIGraphicsEndImageContext();

//以png格式返回指定图片的数据

imageData = UIImagePNGRepresentation(aImage);

18.更改cell选中的背景：

UIView *myview = [[UIView alloc] init];

myview.frame = CGRectMake(0, 0, 320, 47);

myview.backgroundColor = [UIColorcolorWithPatternImage:[UIImage imageNamed:@"0006.png"]];

cell.selectedBackgroundView = myview;:

19.显示图片：

CGRect myImageRect = CGRectMake(0.0f, 0.0f, 320.0f, 109.0f);

UIImageView *myImage = [[UIImageView alloc] initWithFrame:myImageRect];

[myImage setImage:[UIImage imageNamed:@"myImage.png"]];

myImage.opaque = YES; //opaque是否透明

[self.view addSubview:myImage];

20.能让图片适应框的大小（beta）

NSString*imagePath = [[NSBundle mainBundle] pathForResource:@"XcodeCrash"ofType:@"png"];

UIImage *image = [[UIImage alloc]initWithContentsOfFile:imagePath];

UIImage *newImage= [image transformWidth:80.f height:240.f];

UIImageView *imageView = [[UIImageView alloc]initWithImage:newImage];

[newImagerelease];

[image release];

[self.view addSubview:imageView];

21.实现点击图片进行跳转的代码：（生成一个带有背景图片的button，给button绑定想要的事件）

UIButton *imgButton=[[UIButton alloc]initWithFrame:CGRectMake(0, 0, 120, 120)];

[imgButton setBackgroundImage:(UIImage *)[self.imgArray objectAtIndex:indexPath.row] forState:UIControlStateNormal];

imgButton.tag=[indexPath row];

[imgButton addTarget:self action:@selector(buttonClick:) forControlEvents:UIControlEventTouchUpInside];

22.键盘回收：

-（IBAction）textFieldDoneEditing：（id）sender{

[sender resighFirstRespond]；

}

通过点击背景回收键盘：（两个都得添加）

-（IBAction）textFieldDoneEditing：（id）sender{

[sender resighFirstRespond]；

}

-（IBAction）backgroundTapped：（id）sender{

[nameField resignFirstRespond];

[numberField resignFirstRespond];

}