How To Achieve The Best Lookup Performance

This article contains several practical suggestions about how to create effective element lookup queries using location strategies supported by WebDriverAgent. All examples are written using a pseudo-language.

Select The Most Effective Lookup Strategy

By.xpath('//XCUIElementTypeTable') -> 
By.className('XCUIElementTypeTable')

By.xpath('//XCUIElementTypeTable[@name="table"]') -> 
By.accessibilityId('table')

By.xpath('//XCUIElementTypeTable[@name="table"]') -> 
By.predicate('type == "XCUIElementTypeTable" AND name == "table"')

By.xpath('//XCUIElementTypeTable[@name="table" or @label="tableLabel"]') -> 
By.predicate('type == "XCUIElementTypeTable" AND (name == "table" OR label == "tableLabel")')

By.xpath('//XCUIElementTypeTable[@name="table2" or @name="table1"]') -> 
By.predicate('type == "XCUIElementTypeTable" AND name IN {"table2","table1"}')

By.xpath('//XCUIElementTypeTable[@name="table"]/XCUIElementTypeCell[@visible="true"]') ->
By.classChain('**/XCUIElementTypeTable[`name == "table"`]/XCUIElementTypeCell[`visible == 1`]')

By.xpath('//XCUIElementTypeTable[@name="table"]//XCUIElementTypeTextField[@name='input' and @visible="true"]') ->
By.classChain('**/XCUIElementTypeTable[`name == "table"`]/**/XCUIElementTypeTextField[`name == "input" AND visible == 1`]')

By.xpath('//XCUIElementTypeTable[@name="table"]/XCUIElementTypeCell[@visible="true" and .//XCUIElementTypeTextField[@name="input]]') ->
By.classChain('**/XCUIElementTypeTable[`name == "table"`]/**/XCUIElementTypeCell[`visible == 1`][$type == "XCUIElementTypeTextField" AND name == "input"$]')

This is the list of available location strategies sorted by their performance (the first one is the fastest one):

1. Class Name
2. Accessibility Id
3. Link Text
4. Predicate
5. Class Chain
6. XPath

Always try to use the strategy, which is closer to the top of this list. XPath strategy can sometimes be very slow, because it is not natively supported by XCTest and WDA requires additional efforts to implement it, which seriously affects lookup time. Use XPath locators only if there is no other alternative, for example if some special functions or axes are used in the query.

Limit The Search Scope

dstElement = driver.findElement(
  By.xpath('//XCUIElementTypeTable[@name="table"]//XCUIElementTypeTextField[@visible="true"]')) -> 
tableEl = driver.findElement(By.accessibilityId('table'));
dstElement = tableEl.findElement(
  By.predicate('type == "XCUIElementTypeTextField" AND visible == 1'))

The more UI elements in the current search scope you have the longer lookup times you get. By default the search scope is the source of the whole page (expressions like driver.findElement). By limiting it to the source of the particular element (e. g. tableEl.findElement) one can decently optimize lookup performance especially if multiple lookups are going to be executed on the same root element. This strategy can also help to avoid XPath locators or improve lookup times for them if it is executed in the limited scope.

Do Not Search Multiple Elements If Only One Element Is Expected To Be Matched

dstElement = driver.findElements(By.xpath('//XCUIElementTypeTable'))[0] -> 
dstElement = driver.findElement(By.className('XCUIElementTypeTable'))

Usually findElements takes more time to complete than findElement, because it is not necessary to scan through the whole source to find all matches, but rather return after the first one is detected.

Avoid Generic Matchers

By.xpath('//*[@*="1"]/parent::*') -> 
By.xpath('//XCUIElementTypeButton[@name="1"]/parent::XCUIElementTypeCell')

Generic matchers like asterisk * in combination with findElements call may require to scan all the attributes of each UI element, which is quite ineffective from performance perspective.