Test MarginLayoutParams vs LinearLayout.LayoutParams

[swankjesse]

No description provided.

[swankjesse]

This test shows that LinearLayout.LayoutParams has different behavior from ViewGroup.MarginLayoutParams when both are used in a LinearLayout with Paparazzi.

I believe both types have the same behavior on real devices.

It’s unlikely that the root cause of this is Paparazzi; it’s much more likely that layoutlib has the original bug.

I’m unsure of next steps here. We could report it upstream to layoutlib? And we should advise developers to use LinearLayout.LayoutParams when configuring a LinearLayout as that works consistently across platforms.

[swankjesse]

I found the root cause of the difference in behavior. It’s not layoutlib vs. real devices; instead it’s an API-level distinction.

From View.java:

/**
 * Prior to N, some ViewGroups would not convert LayoutParams properly even though both extend
 * MarginLayoutParams. For instance, converting LinearLayout.LayoutParams to
 * RelativeLayout.LayoutParams would lose margin information. This is fixed on N but target API
 * check is implemented for backwards compatibility.
 *
 * {@hide}
 */
protected static boolean sPreserveMarginParamsInLayoutParamConversion;

[swankjesse]

No action to take in Paparazzi on this.