Appium-Android中UiSelector的instance参数含义及取值咨询

Hey there! Let’s break down exactly what the instance() parameter does in your UiSelector code, and how to choose the right value for it.

What does instance() mean? #

When you use className("android.widget.TextView"), UiAutomator scans the entire screen and collects all elements that match the android.widget.TextView class. The instance() method acts as an index to pick a specific element from that matched list. Think of it like pointing to the nth item in a list of results.

What values can instance() take? #

• It accepts zero-based integers (meaning we start counting from 0, not 1).
  • instance(0) targets the first matching element UiAutomator finds in the UI hierarchy.
  • instance(1) targets the second matching element, instance(2) the third, and so on.
• There’s no upper limit beyond the number of matching elements on the screen—if you use an index higher than the number of matches, you’ll get a NoSuchElementException.

Example to make it concrete #

Suppose your screen has three TextView elements in this order: "Dashboard", "Notifications", "Settings".

• new UiSelector().className("android.widget.TextView").instance(0) → targets "Dashboard"
• new UiSelector().className("android.widget.TextView").instance(1) → targets "Notifications"
• new UiSelector().className("android.widget.TextView").instance(2) → targets "Settings"

A quick note: The order of elements in the matched list depends on how UiAutomator traverses the UI hierarchy (typically top-to-bottom, left-to-right, but this can vary based on your app’s layout structure). For more stable tests, it’s better to combine className() with other selectors like text() or resourceId() if those are available—but instance() is super handy when you don’t have unique identifiers to work with.

Your original code:

driver.findElementByAndroidUIAutomator("new UiSelector().className(\"android.widget.TextView\").instance(0)");

This line specifically tells Appium to locate the very first android.widget.TextView element present on the current screen.

内容的提问来源于stack exchange，提问作者Gaurav Singh