问题
Appium has a way to inspect the view hierarchy of an app using an inspector. I am interested in building one myself.
I know the overview answer of: it uses some webdriver to accomplish this. But how? It puzzles me that a separate iOS app can some how communicate to another app, and show even its screen.
How does it work under the hood? or how does the iOS app communicate to the UI inspector to send its screen shots and hierarchy?
回答1:
It puzzles me that a separate iOS app can some how communicate to another app, and show even its screen.
Yes! Apps should not be able to do this. But there exists a special kind of app, built just for testing, which IS able to do this.
The way this is done is using Apple's XCUITest framework. When you write an XCUITest in XCode, it builds a special app which is able to start your test app and then communicate with it using the XCUITest methods. These methods allow you to inspect elements in the view.
In order to create a view tree, you start at the root view and iterate over the children, building out a tree with a tree traversal.
Normally, the XCUITest app exits when your test script finishes, which means you won't be able to access it from a desktop app for viewing the tree as it updates. If you write your test script to run an infinite loop and open a network port for communication with an outside process, now you can build your viewer. This is exactly what Appium does, so I suggest you check out the appium source code and maybe just use that?
More information in this blog post
[edit]: Oh yeah, Appium uses Feacebook's WebDriverAgent project as the script that runs on the app. So WebDriverAgent is basically an XCUITest script which runs a server and can take commands during a test. Appium does a ton of work to bundle and package it into the special kind of companion app that is able to access your app, installs it on the iOS device, and then runs the test. WebDriverAgent has a command which iterates over the UIHierarchy and returns the whole tree.
来源：https://stackoverflow.com/questions/58391393/how-does-a-ui-app-inspectors-like-the-one-in-appium-work