如何让这个ggplot图例和条形图的顺序一致？

# 创建一个数据框
df <- data.frame(
  category = c("A", "B", "C", "D"),
  value = c(10, 20, 30, 40)
)

# 将category列转换为因子，并按照自定义顺序排序
df$category <- factor(df$category, levels = c("B", "D", "A", "C"))

# 绘制条形图
library(ggplot2)
p <- ggplot(df, aes(x = category, y = value, fill = category)) +
  geom_bar(stat = "identity")

# 调整图例顺序
p + scale_fill_manual(values = c("#FF0000", "#00FF00", "#0000FF", "#FFFF00"))