Layout_toleftof = "@ ID/xx" indicates that the control with this ID cannot be found.

When you adjust the layout, You need to place control a on the left of control B. My XML layout file is a control defined from left to right in order, so control a is first defined, then control B is defined in the properties of control.

Android: layout_toleftof = "@ ID/sharebutton" always prompts that I cannot find the sharebutton ID, which is clearly defined later. Why can't eclipse find it?

Later, the toleftof and torightof control parameters you wanted to use must be defined before they are used,

So define control B first and then define control.