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配方列表性能110 行 · 1 个文件

A list too big to build

createView is rare, bindView is constant. Anything slow in bindView — a query, a request, an allocation — is felt directly as stutter while scrolling.

它展示了什么

Fifty thousand rows, and only a screenful of components.

An ordinary list builds one component per item. At a few hundred that is fine and simpler; at fifty thousand it allocates fifty thousand components before the first frame and the app appears to hang on open. VirtualListView keeps only what fits and recycles those as you scroll, so the cost follows the size of the window rather than the size of the data.

That is why the adapter has two methods and not one. createView builds an empty row — rarely, only when the pool runs dry. bindView fills a row that already exists, on every scroll, for every row that comes into view. Building components in bindView defeats the whole thing: it is the recycling that makes this cheap, and allocating in the bind step throws the saving away while keeping the complexity.

The price is that every row is the same height. That is what lets the list work out which items are on screen without measuring any of them, and it is the one case this cannot serve.

在你的机器上运行

每个示例都是普通的 Window，启动器只需要它的名字。

gradlew lwjgl3:run --args="classname dev.cf.recipe.R17BigList"
修改它

Java 是提前编译的，浏览器无法自行重建你的修改 —— 这里的代码在发布前已由 TeaVM 转成 JavaScript。把文件复制到项目里，它在四个平台上原样运行；上面那条命令就是全部准备工作。

正在此处运行CrossFly 0.1.32
正在启动应用…

由 TeaVM 编译为 JavaScript —— 是同一份代码，不是录像。 · 全部示例

它用到了什么

本示例触及的框架类型。带链接的有参考页。

ComponentGapGridLayoutIconBadgeLabelPalColorRelativeStylesVirtualListViewWidgets

源码

完整无删减。这就是那个文件，不是片段。

原始
dev/cf/recipe/R17BigList.java
package dev.cf.recipe;

import dev.cf.Tones;

import dev.crossfly.ui.*;
import dev.crossfly.ui.color.*;
import dev.crossfly.ui.graphics.*;
import dev.crossfly.ui.layout.*;
import dev.crossfly.ui.style.*;

import static dev.crossfly.ui.Widgets.*;

/**
 * Fifty thousand rows, and only a screenful of components.
 *
 * <p>An ordinary list builds one component per item. At a few hundred that is fine and simpler; at
 * fifty thousand it allocates fifty thousand components before the first frame and the app appears
 * to hang on open. {@link VirtualListView} keeps only what fits and <b>recycles</b> those as you
 * scroll, so the cost follows the size of the window rather than the size of the data.</p>
 *
 * <p>That is why the adapter has two methods and not one. {@code createView} builds an empty row —
 * rarely, only when the pool runs dry. {@code bindView} fills a row that already exists, on every
 * scroll, for every row that comes into view. <b>Building components in bindView defeats the whole
 * thing</b>: it is the recycling that makes this cheap, and allocating in the bind step throws the
 * saving away while keeping the complexity.</p>
 *
 * <p>The price is that every row is the same height. That is what lets the list work out which
 * items are on screen without measuring any of them, and it is the one case this cannot serve.</p>
 */
public class R17BigList extends Recipe
{
   private static final int COUNT = 50000;

   public String title()
   {
      return "A list too big to build";
   }

   public String note()
   {
      return "createView is rare, bindView is constant. Anything slow in bindView — a query, a"
         + " request, an allocation — is felt directly as stutter while scrolling.";
   }

   /**
    * One row, holding references to the parts that change.
    *
    * <p>Keeping the labels as fields is the point: {@code bindView} then sets two strings, with no
    * tree walk and no allocation. Looking the labels up by tag on every bind would work and would
    * put a search into the scroll path.</p>
    */
   private static class Row extends Component
   {
      final Label name = label("", 1f, true, Styles.textColor, Position.START);
      final Label code = label("", 1f, false, Styles.captionColor, Position.END);
      final IconBadge tile = Tones.tile("", Tones.accent());

      Row() throws Exception
      {
         setLayout(new GridLayout(Position.START, Position.CENTER));
         getStyle().ingap(Gap.ofFont(.8f, .3f, .8f, .3f));
         add(0f, .7f, .3f, tile, outgap(name, .6f, 0, 0, 0), code);
      }

      /**
       * Repaints the tile for the row's new index.
       *
       * <p>A recycled view keeps whatever the last index left on it, so the colour has to be
       * re-bound exactly like the text is. Miss this and the list looks right until you scroll,
       * and then the tiles stop matching the numbers — the classic recycler bug, worth showing
       * in the recipe that is about recycling.</p>
       */
      void tone(int index)
      {
         PalColor t = Tones.cycle(index);
         tile.text(String.valueOf((char) ('A' + index % 26)));
         tile.getStyle()
            .backColor(t.withAlpha(0x24))
            .textColor(t);
      }
   }

   public void build(Component body) throws Exception
   {
      VirtualListView list = new VirtualListView(Relative.ofFont(3.2f),
         new VirtualListView.DataAdapter()
         {
            public int getCount()
            {
               return COUNT;
            }

            public Component createView() throws Exception
            {
               return new Row();
            }

            public void bindView(Component view, int index)
            {
               Row r = (Row) view;
               r.name.setText("Item " + (index + 1));
               r.code.setText("#" + (100000 + index));
               r.tone(index);
            }
         });
      list.testTag("recipe.biglist");
      body.add(LAY_FILL, list);
   }
}
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