React-native Demo (1)

Today put react native environment to complete, and then run a small demo to try.
First Environmental configuration & Hello World Summary

According to the above study article, I basically completed, but in the configuration process encountered 2 problems, need to end. node is installed

Since I installed react-native before I installed node, we would have an error when executing, this is because react-native is using io.js, This time we need to install io.js, and you have to delete node, I follow the tutorial on the solution using Brew unlink node, to remove the reference to node, and then install IOJS, but the use of sudo brew link Iojs--force will be error:

58demacbook-pro:react-native wuxian$ sudo brew link iojs--force
linking/usr/local/cellar/iojs/2.5.0 ... 
Error:could not symlink bin/node
Target/usr/local/bin/node
already exists. Want to remove it:
  rm '/usr/local/bin/node ' to force the

link and overwrite all conflicting files:
  bre W link--overwrite iojs to

list all files, would be deleted:
  brew link--overwrite--dry-run iojs

Workaround

This time we're going to use sudo brew link--overwrite iojs--force to cover node. js with Iojs. error for null pointer

After I initialize a HelloWorld project, I get an error and report a null pointer.

Nsurlsessiondownloadtask *task = [_urlsession downloadtaskwithurl:url completionhandler:nil];

I changed it to an empty implementation:

 NSURLSessionDownloadTask *task = [_URLSession downloadTaskWithURL:url completionHandler:^(NSURL *location, NSURLResponse *response, NSError *error){
  }];

The program is running successfully.

Then I found another solution to the problem on GitHub

It is correct to delete the Completionhandler:nil of the method after it becomes the following form:

Nsurlsessiondownloadtask *task = [_urlsession Downloadtaskwithurl:url];