//api注册
api = WXAPIFactory.createWXAPI(this, "APP_ID", true);
api.registerApp("APP_ID");
SendAuth.Req req = new SendAuth.Req();
//授权读取用户信息
req.scope = "snsapi_userinfo";
//自定义信息
req.state = "wechat_sdk_demo_test";
//向微信发送请求
api.sendReq(req);

public class WXEntryActivity extends Activity implements IWXAPIEventHandler{
  @Override
  public void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    //注册API
    api = WXAPIFactory.createWXAPI(this, "APP_ID");
    api.handleIntent(getIntent(), this);
  }
  @Override
  public void onResp(BaseResp resp) {
    if(resp instanceof SendAuth.Resp){
      SendAuth.Resp newResp = (SendAuth.Resp) resp;
      //获取微信传回的code
      String code = newResp.code;
    }
  }
}