Question

Sun_SSH_1.1.4, SSH protocols 1.5/2.0, OpenSSL 0x0090704f
debug1: Reading configuration data /etc/ssh/ssh_config
debug1: Rhosts Authentication disabled, originating port will not be trusted.
debug1: ssh_connect: needpriv 0
debug1: Connecting to 192.168.232.250 [192.168.232.250] port 22.
debug1: Connection established.
debug1: identity file /etc/ssh_host_key type 0
debug2: key_type_from_name: unknown key type '-----BEGIN'
debug2: key_type_from_name: unknown key type '-----END'
debug1: identity file /etc/ssh_host_rsa_key type 1
debug2: key_type_from_name: unknown key type '-----BEGIN'
debug2: key_type_from_name: unknown key type '-----END'
debug1: identity file /etc/ssh_host_dsa_key type 2
debug1: Logging to host: 192.168.232.250
debug1: Local user: root Remote user: root
debug1: Remote protocol version 2.0, remote software version mpSSH_0.2.0
debug1: no match: mpSSH_0.2.0
debug1: Enabling compatibility mode for protocol 2.0
debug1: Local version string SSH-2.0-Sun_SSH_1.1.4
debug1: use_engine is 'yes'
debug1: pkcs11 engine initialized, now setting it as default for RSA, DSA, and symmetric ciphers
debug1: pkcs11 engine initialization complete

**debug2: kex_parse_kexinit: diffie-hellman-group-exchange-sha1,diffie-hellman-group14-sha1,diffie-hellman-group1-sha1
debug2: kex_parse_kexinit: ssh-rsa,ssh-dss
debug2: kex_parse_kexinit: aes128-ctr,aes128-cbc,arcfour,3des-cbc,blowfish-cbc
debug2: kex_parse_kexinit: aes128-ctr,aes128-cbc,arcfour,3des-cbc,blowfish-cbc
debug2: kex_parse_kexinit: hmac-md5,hmac-sha1,hmac-sha1-96,hmac-md5-96
debug2: kex_parse_kexinit: hmac-md5,hmac-sha1,hmac-sha1-96,hmac-md5-96
debug2: kex_parse_kexinit: none,zlib
debug2: kex_parse_kexinit: none,zlib
debug2: kex_parse_kexinit: i-default
debug2: kex_parse_kexinit: i-default
debug2: kex_parse_kexinit: first_kex_follows 0
debug2: kex_parse_kexinit: reserved 0**

debug1: Failed to acquire GSS-API credentials for any mechanisms (No credentials were supplied, or the credentials were unavailable or inaccessible
Unknown code 0
)
debug1: SSH2_MSG_KEXINIT sent
debug1: SSH2_MSG_KEXINIT received

**debug2: kex_parse_kexinit: diffie-hellman-group-exchange-sha1,diffie-hellman-group14-sha1,diffie-hellman-group1-sha1
debug2: kex_parse_kexinit: ssh-rsa,ssh-dss
debug2: kex_parse_kexinit: aes128-ctr,aes128-cbc,arcfour,3des-cbc,blowfish-cbc
debug2: kex_parse_kexinit: aes128-ctr,aes128-cbc,arcfour,3des-cbc,blowfish-cbc
debug2: kex_parse_kexinit: hmac-md5,hmac-sha1,hmac-sha1-96,hmac-md5-96
debug2: kex_parse_kexinit: hmac-md5,hmac-sha1,hmac-sha1-96,hmac-md5-96
debug2: kex_parse_kexinit: none,zlib
debug2: kex_parse_kexinit: none,zlib
debug2: kex_parse_kexinit: i-default
debug2: kex_parse_kexinit: i-default
debug2: kex_parse_kexinit: first_kex_follows 0
debug2: kex_parse_kexinit: reserved 0
debug2: kex_parse_kexinit: diffie-hellman-group1-sha1
debug2: kex_parse_kexinit: ssh-rsa,ssh-dss
debug2: kex_parse_kexinit: aes128-cbc,3des-cbc
debug2: kex_parse_kexinit: aes128-cbc,3des-cbc
debug2: kex_parse_kexinit: hmac-md5,hmac-sha1
debug2: kex_parse_kexinit: hmac-md5,hmac-sha1
debug2: kex_parse_kexinit: none
debug2: kex_parse_kexinit: none
debug2: kex_parse_kexinit:
debug2: kex_parse_kexinit:
debug2: kex_parse_kexinit: first_kex_follows 0
debug2: kex_parse_kexinit: reserved 0**

debug2: mac_init: found hmac-md5
debug1: kex: server->client aes128-cbc hmac-md5 none
debug2: mac_init: found hmac-md5
debug1: kex: client->server aes128-cbc hmac-md5 none
debug1: Peer sent proposed langtags, ctos:
debug1: Peer sent proposed langtags, stoc:
debug1: We proposed langtags, ctos: i-default
debug1: We proposed langtags, stoc: i-default
debug1: dh_gen_key: priv key bits set: 118/256
debug1: bits set: 504/1024
debug1: sending SSH2_MSG_KEXDH_INIT
debug1: expecting SSH2_MSG_KEXDH_REPLY
Warning: Permanently added '192.168.232.250' (RSA) to the list of known hosts.
debug1: bits set: 518/1024
debug1: ssh_rsa_verify: signature correct
debug2: kex_derive_keys
debug1: newkeys: mode 1
debug1: set_newkeys: setting new keys for 'out' mode
debug1: SSH2_MSG_NEWKEYS sent
debug1: expecting SSH2_MSG_NEWKEYS
debug1: newkeys: mode 0
debug1: set_newkeys: setting new keys for 'in' mode
debug1: SSH2_MSG_NEWKEYS received
debug1: done: ssh_kex2.
debug1: send SSH2_MSG_SERVICE_REQUEST
debug2: service_accept: ssh-userauth
debug1: got SSH2_MSG_SERVICE_ACCEPT
debug1: Authentications that can continue: password,publickey
debug1: Next authentication method: publickey
debug1: Trying public key: /etc/ssh_host_rsa_key
debug2: we sent a publickey packet, wait for reply
debug1: Authentications that can continue: password,publickey
debug1: Trying public key: etc/ssh_host_dsa_key
debug2: we sent a publickey packet, wait for reply
debug1: Authentications that can continue: password,publickey
debug2: we did not send a packet, disable method
debug1: Next authentication method: password

LineChartView是Charts库中的类

我将Serial AccessQueue与LineChartView和color变量一起用于线程安全工作。当在DispatchQueue.main上调用super.draw（rect）时，我看到空白的空白屏幕。

我调试了LineChartView的draw（），发现UIGraphicsGetCurrentContext（）返回nil。为什么？

Answer 1

UIKit希望所有绘图都在主线程上完成。如果要绘制背景，则需要在CALayer级别使用Core图形。请参阅CALayer.drawsAsynchronously

的文档

Answer 2

将此视图视为当前图形上下文，因为它会在drawRect开始运行之前自动打开，并在其结束时自动关闭。

现在考虑异步对于“完成”概念的含义。我们从当前的运行循环返回，并且在任何异步代码都无法开始之前就关上了门。

所以您的代码是这样的：

// the door opens
override func draw(_ rect: CGRect) {
    accessQueue.async {
        // the door closes
        self.updateColors()
        DispatchQueue.main.async {
            super.draw(rect)
        }
    }
}

门一旦关闭，就没有当前的图形上下文，所有绘图命令也无处可去。因此，您的整个代码是无用的。

调试LineChartView的draw（）并发现UIGraphicsGetCurrentContext（）返回nil。为什么？

这就是原因。到代码运行时，不再有图形上下文。

UIView draw（_ rect：CGRect）不适用于多线程

2 个答案: