public static GUILayoutOption ExpandWidth (bool expand);

説明

コントロールの水平方向の拡張を許可/禁止するオプション

If this is true, the enclosed UI elements can expand to fill the available horizontal width.

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using UnityEngine;
using System.Collections;

public class ExampleClass : MonoBehaviour { void OnGUI() { GUILayout.BeginVertical(); GUILayout.Button("Short Button", GUILayout.ExpandWidth(false)); GUILayout.Button("Very very long Button"); GUILayout.EndVertical(); } }