Android Studio：在xml属性中，竖线到底是什么意思？

Question

I am confused as to what exactly the | means in the following context:

android:layout_gravity="center_vertical|center_horizontal"

Is the definition of the use of this symbol specified anywhere, in case I come across others?

Answer 1

It means that it has both flags enabled, center_vertical and center_horizontal.

In the Java side, the pipe is a bitwise OR operation, which is commonly used to store flags, which are then checked using a bitwise AND (& operator) operation.

Answer 2

android:layout_gravity determines gravity which view specifies to its parent thus position which it would like to "take" in the parent to which it belongs to.

Generally you can read about attributes at Android dev site: https://developer.android.com/reference/android/widget/LinearLayout.LayoutParams.html

Answer 3

Some attributes accept more than one value, like layout_gravity. The | character separe these values, in that case meaning that your layout gonna take both gravities, center_vertical and center_horizontal. You could simply this by using:

android:layout_gravity="center"

You can combine this constants in order to position your content in relation to it parent: https://developer.android.com/reference/android/R.attr.html#layout_gravity

Other examples of attributes that take more than one value:

android:gravity="left|bottom"

android:inputType="textMultiLine|textCapSentences"

android:gravity="left|bottom"

android:foregroundGravity="fill_horizontal|top"

android:inputType="text|textAutoComplete|textNoSuggestions"

android:windowSoftInputMode="adjustResize|stateHidden"

android:configChanges="keyboardHidden|orientation|screenSize"