PS：很基礎(chǔ)的東西割择，記錄一下腻豌，用起來(lái)方便些犬第。

按iOS版本分：
iOS5，6：320 x 480(1x) 响牛、640 x 960(2x)、 640 × 1136(Retina 4)
iOS8赫段，9：1242 × 2208(Retina HD 5.5″)呀打、 750 × 1334(Retina HD 4.7″)
iOS7-9 ：640 × 960(2x) 、640 × 1136(Retina 4)
iOS11+：1125?×?2436（3x）糯笙。蘋(píng)果X的贬丛。

所以，4/4s需要2張给涕。5/5s需要2張豺憔。6/7/8需要1張。對(duì)應(yīng)的plus需要1張够庙。iPhoneX需要1張恭应。（3GS可以忽略了）共計(jì)7張圖片。
對(duì)應(yīng)Assets.xcassets文件夾中的Contents.json文件耘眨。其中filename需要和圖片名一致昼榛。

{
  "images" : [
    {
      "extent" : "full-screen",
      "idiom" : "iphone",
      "subtype" : "2436h",
      "filename" : "startpage_iPhoneX_1125x2436pt@3x.png",
      "minimum-system-version" : "11.0",
      "orientation" : "portrait",
      "scale" : "3x"
    },
    {
      "extent" : "full-screen",
      "idiom" : "iphone",
      "subtype" : "736h",
      "filename" : "startpage_plus_iOS89_414x736pt@3x.png",
      "minimum-system-version" : "8.0",
      "orientation" : "portrait",
      "scale" : "3x"
    },
    {
      "extent" : "full-screen",
      "idiom" : "iphone",
      "subtype" : "667h",
      "filename" : "startpage_iPhone678_iOS89_375x667pt@2x.png",
      "minimum-system-version" : "8.0",
      "orientation" : "portrait",
      "scale" : "2x"
    },
    {
      "extent" : "full-screen",
      "idiom" : "iphone",
      "subtype" : "retina4",
      "filename" : "startpage_iPhone5_iOS789_320x568pt@2x.png",
      "minimum-system-version" : "7.0",
      "orientation" : "portrait",
      "scale" : "2x"
    },
    {
      "orientation" : "portrait",
      "idiom" : "iphone",
      "filename" : "startpage_iPhone5_iOS56_320x568pt@2x.png",
      "extent" : "full-screen",
      "subtype" : "retina4",
      "scale" : "2x"
    },
    {
      "orientation" : "portrait",
      "idiom" : "iphone",
      "filename" : "startpage_iPhone4_iOS789_320x480pt@2x.png",
      "extent" : "full-screen",
      "minimum-system-version" : "7.0",
      "scale" : "2x"
    },
    {
      "orientation" : "portrait",
      "idiom" : "iphone",
      "filename" : "startpage_iPhone4_iOS56_320x480pt@2x.png",
      "extent" : "full-screen",
      "scale" : "2x"
    },
    {
      "orientation" : "portrait",
      "idiom" : "iphone",
      "filename" : "startpage_iPhone3GS_iOS56_320x480pt.png",
      "extent" : "full-screen",
      "scale" : "1x"
    }
  ],
  "info" : {
    "version" : 1,
    "author" : "xcode"
  }
}