Please solve the programming task below using a self-contained code snippet in a markdown code block.

You are given a 0-indexed integer array nums and an integer threshold.
Find the length of the longest subarray of nums starting at index l and ending at index r (0 <= l <= r < nums.length) that satisfies the following conditions:

nums[l] % 2 == 0
For all indices i in the range [l, r - 1], nums[i] % 2 != nums[i + 1] % 2
For all indices i in the range [l, r], nums[i] <= threshold

Return an integer denoting the length of the longest such subarray.
Note: A subarray is a contiguous non-empty sequence of elements within an array.
 
Please complete the following python code precisely:
```python
class Solution:
    def longestAlternatingSubarray(self, nums: List[int], threshold: int) -> int:
```