UiSelector.resourceId("myButtonId") not working

I'm trying to get the facebook Login button in UIautomator but its failing to find the button given the id of the button
```

```
And here is the code how I'm accessing the button in my test case
`UiObject facebookButton = mDevice.findObject(new UiSelector().resourceId("login_button_facebook"));`

Its failing to find the button saying :
```
android.support.test.uiautomator.UiObjectNotFoundException: UiSelector[RESOURCE_ID=login_button_facebook]
at android.support.test.uiautomator.UiObject.click(UiObject.java:416)
```
Please let me know if I'm doing it wrong.
The documentation has not much detail about how to use it.

从布局 XML 和调用 UiSelector.resourceId("login_button_facebook") 的测试用例开始，然后阅读与报告的 UiObjectNotFoundException 相关的 UiSelector.resourceId 和 UiObject API。根据已渲染的 Facebook 登录按钮确认选择器行为，并验证测试能够找到并点击它。

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