Cat learn iOS (51) Multi-threaded network GCD Download merged pictures _ use of queue groups

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Merge picture (picture watermark) The first method effect

Realize:

Ideas:
1. Download 2 pictures respectively: Big picture, LOGO
2. Merge 2 photos
3. Display to a ImageView body

  //Asynchronous Download    Dispatch_async(Dispatch_get_global_queue (Dispatch_queue_priority_default,0), ^{//1. Download the 1th one        Nsurl*URL1 = [Nsurlurlwithstring:@"Http://g.hiphotos.baidu.com/image/pic/item/f2deb48f8c5494ee460de6182ff5e0fe99257e80.jpg"]; NSData *data1 = [NSData DATAWITHCONTENTSOFURL:URL1];UIImage*image1 = [UIImageIMAGEWITHDATA:DATA1];//2. Download the 2nd one        Nsurl*URL2 = [Nsurlurlwithstring:@"Http://su.bdimg.com/static/superplus/img/logo_white_ee663702.png"]; NSData *data2 = [NSData datawithcontentsofurl:url2];UIImage*image2 = [UIImageIMAGEWITHDATA:DATA2];//3. Merging pictures        //Open a bitmap contextUigraphicsbeginimagecontextwithoptions (Image1. Size,NO,0.0);//Draw 1th picture        CGFloatIMAGE1W = Image1. Size. Width;CGFloatimage1h = Image1. Size. Height; [Image1 Drawinrect:cgrectmake (0,0, IMAGE1W, image1h)];//Draw 2nd picture        CGFloatimage2w = Image2. Size. Width*0.5;CGFloatIMAGE2H = Image2. Size. Height*0.5;CGFloatimage2y = image1h-image2h; [Image2 Drawinrect:cgrectmake (0, image2y, image2w, image2h)];//Get the picture in context        UIImage*fullimage = Uigraphicsgetimagefromcurrentimagecontext ();//End ContextUigraphicsendimagecontext ();//4. Back to the main thread display picture        Dispatch_async(Dispatch_get_main_queue (), ^{ Self. ImageView. Image= Fullimage;    }); });

But this is done in an asynchronous thread, but when the first diagram is downloaded, the second graph is still waiting, and we want each diagram to be downloaded in a separate asynchronous thread, so we use the second method.

: The second method

First define two ImageView

@property (weaknonatomicIBOutletUIImageView *imageView;@property (nonatomicstrongUIImage *image1;@property (nonatomicstrongUIImage *image2;

And then implement this implementation

 //Asynchronous Download    Dispatch_async(Dispatch_get_global_queue (Dispatch_queue_priority_default,0), ^{//1. Download the 1th one        Nsurl*URL1 = [Nsurlurlwithstring:@"Http://g.hiphotos.baidu.com/image/pic/item/f2deb48f8c5494ee460de6182ff5e0fe99257e80.jpg"]; NSData *data1 = [NSData DATAWITHCONTENTSOFURL:URL1]; Self. Image1= [UIImageIMAGEWITHDATA:DATA1]; [ SelfBindimages]; });Dispatch_async(Dispatch_get_global_queue (Dispatch_queue_priority_default,0), ^{//2. Download the 2nd one        Nsurl*URL2 = [Nsurlurlwithstring:@"Http://su.bdimg.com/static/superplus/img/logo_white_ee663702.png"]; NSData *data2 = [NSData datawithcontentsofurl:url2]; Self. Image2= [UIImageIMAGEWITHDATA:DATA2]; [ SelfBindimages]; });

It works by opening two asynchronous threads to download two images, which will be called after the download is complete.
"Self bindimages" method, this time we set in the S method back to the main interface refresh, but first to determine whether the two graphs have data, as follows:

- (void) bindimages{if( Self. Image1==Nil|| Self. Image2==Nil)return;//3. Merging pictures    //Open a bitmap contextUigraphicsbeginimagecontextwithoptions ( Self. Image1. Size,NO,0.0);//Draw 1th picture    CGFloatIMAGE1W = Self. Image1. Size. Width;CGFloatimage1h = Self. Image1. Size. Height; [ Self. Image1Drawinrect:cgrectmake (0,0, IMAGE1W, image1h)];//Draw 2nd picture    CGFloatimage2w = Self. Image2. Size. Width*0.5;CGFloatIMAGE2H = Self. Image2. Size. Height*0.5;CGFloatimage2y = image1h-image2h; [ Self. Image2Drawinrect:cgrectmake (0, image2y, image2w, image2h)];//Get the picture in context    UIImage*fullimage = Uigraphicsgetimagefromcurrentimagecontext ();//End ContextUigraphicsendimagecontext ();//4. Back to the main thread display picture    Dispatch_async(Dispatch_get_main_queue (), ^{ Self. ImageView. Image= Fullimage; });}

Although we solve the problem through our own ideas, we have a better solution, that is, the queue group

Third method: When does queue group complete use queue group?

First: Perform 2 time-consuming operations asynchronously, respectively
Second: Wait for 2 asynchronous operations to complete, then return to the main thread to perform the operation

If you want to implement these requirements quickly and efficiently, consider using queue groups, as follows:

// 1.创建队列组group =  dispatch_group_create();// 2.1第一个队列组异步dispatch_group_async(group0), ^{    // 执行1个耗时的异步操作});// 2.2第二个队列组异步dispatch_group_async(group0), ^{    // 执行1个耗时的异步操作});// 3.所有队列组异步线程结束后dispatch_group_notify(group, dispatch_get_main_queue(), ^{    // 等前面的异步操作都执行完毕后，回到主线程...});

Then let's do it with the queue group, the code is as follows:

//1. Queue Groupdispatch_group_t group = Dispatch_group_create ();dispatch_queue_tQueue = Dispatch_get_global_queue (Dispatch_queue_priority_default,0);//2. Download Picture 1__blockUIImage*image1 =Nil; Dispatch_group_async (group, queue, ^{Nsurl*URL1 = [Nsurlurlwithstring:@"Http://g.hiphotos.baidu.com/image/pic/item/f2deb48f8c5494ee460de6182ff5e0fe99257e80.jpg"];        NSData *data1 = [NSData DATAWITHCONTENTSOFURL:URL1]; Image1 = [UIImageIMAGEWITHDATA:DATA1]; });//3. Download Picture 2__blockUIImage*image2 =Nil; Dispatch_group_async (group, queue, ^{Nsurl*URL2 = [Nsurlurlwithstring:@"Http://su.bdimg.com/static/superplus/img/logo_white_ee663702.png"];        NSData *data2 = [NSData datawithcontentsofurl:url2]; Image2 = [UIImageIMAGEWITHDATA:DATA2]; });//4. Merge pictures (ensure that after all tasks in the group are executed, the block inside the Notify function is executed)Dispatch_group_notify (group, queue, ^{//Open a bitmap contextUigraphicsbeginimagecontextwithoptions (Image1. Size,NO,0.0);//Draw 1th picture        CGFloatIMAGE1W = Image1. Size. Width;CGFloatimage1h = Image1. Size. Height; [Image1 Drawinrect:cgrectmake (0,0, IMAGE1W, image1h)];//Draw 2nd picture        CGFloatimage2w = Image2. Size. Width*0.5;CGFloatIMAGE2H = Image2. Size. Height*0.5;CGFloatimage2y = image1h-image2h; [Image2 Drawinrect:cgrectmake (0, image2y, image2w, image2h)];//Get the picture in context        UIImage*fullimage = Uigraphicsgetimagefromcurrentimagecontext ();//End ContextUigraphicsendimagecontext ();//5. Back to the main thread display picture        Dispatch_async(Dispatch_get_main_queue (), ^{ Self. ImageView. Image= Fullimage;    }); });

__block keywords

Note: Here we use a __block keyword, because if not added, the block is not allowed to access the outside of the block of things.

Small Summary: Open asynchronous

(Direct knock Dispatch_a ... Can come out a bunch of hints, and then choose to fill, no difficulty, said before.

dispatch_async(dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, 0), ^{    code});

To open a queue group:

First build a queue group:

dispatch_group_t group =  dispatch_group_create();

Then change the queue to a queue and use Dispatch_get_global_queue.

dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, 0), ^{    // 执行1个耗时的异步操作});

You can get a few more on the top, and a couple of threads.

And then at the end, use this:

dispatch_group_notify(group, dispatch_get_main_queue(), ^{    // 等前面的异步操作都执行完毕后，回到主线程...});

The process of merging pictures

Steps:
1. Open a Bitmap context
2.1 Drawing the 1th picture
2.2 Drawing the 2nd picture
3. Get the picture in context
4. End Context

//1. Open a bitmap contextUigraphicsbeginimagecontextwithoptions (Image1. Size,NO,0.0);///2.1 Draw 1th Picture        CGFloatIMAGE1W = Image1. Size. Width;CGFloatimage1h = Image1. Size. Height; [Image1 Drawinrect:cgrectmake (0,0, IMAGE1W, image1h)];///2.2 Draw 2nd picture        CGFloatimage2w = Image2. Size. Width*0.5;CGFloatIMAGE2H = Image2. Size. Height*0.5;CGFloatimage2y = image1h-image2h; [Image2 Drawinrect:cgrectmake (0, image2y, image2w, image2h)];//3. Get the picture in context        UIImage*fullimage = Uigraphicsgetimagefromcurrentimagecontext ();//4. End ContextUigraphicsendimagecontext ();

Cat learn iOS (51) Multi-threaded network GCD Download merged pictures _ use of queue groups