appium安卓7.0以上报错：Original error: Command failed: ps: uiautomator，及sessionId":null的情况

appium安卓7.0以上报错：Original error: Command failed: ps: uiautomator

解决方法：步骤如下

1.找到appium的安装目录下的adb.js文件，目录为：Appium\node_modules\appium\node_modules\appium-adb\lib 

2.打开adb.js，找到如下代码：

ADB.prototype.shell = function (cmd, cb) {
if (cmd.indexOf('"') === -1) {
cmd = '"' + cmd + '"';
}
var execCmd = 'shell ' + cmd;
this.exec(execCmd, cb);
};

在上段代码后添加如下代码：

ADB.prototype.shell_grep = function (cmd, grep, cb) {
if (cmd.indexOf('"') === -1) {
cmd = '"' + cmd + '"';
}
var execCmd = 'shell ' + cmd + '| grep ' + grep;
this.exec(execCmd, cb);
};

　　

3.找到如下代码：

ADB.prototype.getPIDsByName = function (name, cb) {
logger.debug("Getting all processes with '" + name + "'");
this.shell("ps '" + name + "'", function (err, stdout) {
if (err) return cb(err);
stdout = stdout.trim();
var procs = [];
var outlines = stdout.split("\n");
outlines.shift();
_.each(outlines, function (outline) {
if (outline.indexOf(name) !== -1) {
procs.push(outline);
}
});
if (procs.length < 1) {
logger.debug("No matching processes found");
return cb(null, []);
}
var pids = [];
_.each(procs, function (proc) {
var match = /[^\t ]+[\t ]+([0-9]+)/.exec(proc);
if (match) {
pids.push(parseInt(match[1], 10));
}
});
if (pids.length !== procs.length) {
var msg = "Could not extract PIDs from ps output. PIDS: " +
JSON.stringify(pids) + ", Procs: " + JSON.stringify(procs);
return cb(new Error(msg));
}
cb(null, pids);
});
};

把如上代码注释掉，添加如下代码：

ADB.prototype.getPIDsByName = function (name, cb) {
logger.debug("Getting all processes with '" + name + "'");
this.shell_grep("ps", name, function (err, stdout) {
if (err) {
logger.debug("No matching processes found");
return cb(null, []);
}
var pids = [];
_.each(procs, function (proc) {
var match = /[^\t ]+[\t ]+([0-9]+)/.exec(proc);
if (match) {
pids.push(parseInt(match[1], 10));
}
});
if (pids.length !== procs.length) {
var msg = "Could not extract PIDs from ps output. PIDS: " +
JSON.stringify(pids) + ", Procs: " + JSON.stringify(procs);
return cb(new Error(msg));
}
cb(null, pids);
});
};

　　

4.重启appium，问题解决