[null,null,["最后更新时间 (UTC)：2025-07-25。"],[[["\u003cp\u003e\u003ccode\u003eui.Panel\u003c/code\u003e objects arrange widgets within a UI and use layouts to control their display, offering two options: flow and absolute.\u003c/p\u003e\n"],["\u003cp\u003e\u003ccode\u003eui.root\u003c/code\u003e is the main panel in the Code Editor, initially containing the default map, which can be cleared or modified by adding widgets.\u003c/p\u003e\n"],["\u003cp\u003eFlow layouts arrange widgets sequentially in a row or column, with stretching options to fill available space within the panel.\u003c/p\u003e\n"],["\u003cp\u003eAbsolute layouts position widgets based on the \u003ccode\u003eposition\u003c/code\u003e property in their style, allowing precise placement within the panel.\u003c/p\u003e\n"],["\u003cp\u003eThe \u003ccode\u003ewidgets()\u003c/code\u003e method allows direct manipulation of a panel's widget list, enabling dynamic updates and changes to the UI.\u003c/p\u003e\n"]]],[],null,["# Panels and Layouts\n\nPanels\n------\n\nA `ui.Panel` is an upper-level UI container in which to arrange widgets. Each\n`ui.Panel` has a `ui.Panel.Layout` object that controls how its\nwidgets are arranged on the screen. Learn more in the [Layouts\nsection](/earth-engine/guides/ui_panels#layouts). Panels also maintain a list of widgets (which could include other panels)\nthat have been added to them. To manage widgets in the panel, either `add()`\nor `remove()` them from the panel, or retrieve the list of widgets by calling\n`widgets()` on the panel. The widgets list is an instance of\n`ui.data.ActiveList`, which means that you can configure the panel by manipulating\nthe list and the widgets in it.\n\nui.root\n-------\n\nThe `ui.root` is a fixed instance of a `ui.Panel` for everything\nin the Code Editor below the horizontal bar. By default, it contains only a single\nwidget: the default map. Specifically, the item at `ui.root.widgets().get(0)`\nis the `Map` object (an instance of `ui.Map`) that is displayed\nby default in the Code Editor). In addition to the `Map` alias, the only\nother special thing about the default Map is that it has geometry editing tools in it. To\nobtain an empty canvas in which to build your UI, `clear()` the default map\nout of `ui.root`:\n\n### Code Editor (JavaScript)\n\n```javascript\nui.root.clear();\n```\n\nAlternatively, it's possible to modify the default map in the root panel by adding\nwidgets to it. Specifically, think of a map as a panel with an absolute layout (see the\n[Layouts section](/earth-engine/guides/ui_panels#layouts) for details). The following example\nillustrates a modification of the default map:\n\n### Code Editor (JavaScript)\n\n```javascript\n// Load a VIIRS surface reflectance image and display on the map.\nvar image = ee.Image('NOAA/VIIRS/001/VNP09GA/2022_06_05').select('M.*');\nMap.addLayer(image, {bands: ['M5', 'M4', 'M3'], min: 0, max: 4e3, gamma: 1.5});\n\n// Create the title label.\nvar title = ui.Label('Click to inspect');\ntitle.style().set('position', 'top-center');\nMap.add(title);\n\n// Create a panel to hold the chart.\nvar panel = ui.Panel();\npanel.style().set({\n width: '400px',\n position: 'bottom-right'\n});\nMap.add(panel);\n\n// Register a function to draw a chart when a user clicks on the map.\nMap.style().set('cursor', 'crosshair');\nMap.onClick(function(coords) {\n panel.clear();\n var point = ee.Geometry.Point(coords.lon, coords.lat);\n var chart = ui.Chart.image.regions(image, point, null, 30);\n chart.setOptions({title: 'Band values'});\n panel.add(chart);\n});\n```\n\nNote that the example modifies the default map (which is `Map`) by treating\nit as a panel and adding widgets to it. Because maps have absolute layout, the position\nof a widget on a map is determined by a `position` property of the\n`style` property of the widget. See the [absolute\nlayout section](/earth-engine/guides/ui_panels#absolute) for details.\n\nWhen you share a Code Editor link with another user, by default the `ui.root`\ntakes up most of the window, and the text editor, docs panel, and console are hidden. By\ncontrolling the `ui.root` layout, you can control how other users experience\nyour script.\n\nLayouts\n-------\n\nLayouts control how widgets in a panel are arranged for display. There are two layout\noptions, described below: flow layout and absolute layout. Layouts are specified with\nthe `ui.Panel.Layout` class. Set a panel's layout either in the constructor\nor with `setLayout()`. The order in which widgets are added determines\nhow widgets are arranged in a panel with flow layout. The `position` property\neach widget's `style` determines how a widget will be arranged in a panel\nwith absolute layout. If the style on a widget is irrelevant for the layout in which\nthe widget is placed, it's ignored.\n\n### Flow\n\nA flow layout displays widgets in a row (`'horizontal'`) or a column\n(`'vertical'`). The widgets are arranged according to the order in which\nthey are added to the panel. For example, consider the following buttons added to a panel:\n\n### Code Editor (JavaScript)\n\n```javascript\n// Create a panel with vertical flow layout.\nvar panel = ui.Panel({\n layout: ui.Panel.Layout.flow('vertical'),\n style: {width: '300px'}\n});\n\n// Add a bunch of buttons.\nfor (var i = 0; i \u003c 30; i++) {\n panel.add(ui.Button({label: 'Button ' + i, style: {stretch: 'horizontal'}}));\n}\n\nui.root.clear();\nui.root.add(panel);\n```\n\nThe vertical layout should look something like:\n\nNote that the `width` of the panel is set to 300 pixels and the\n`stretch` is set to `'horizontal'` with the `style`\nproperty. The `stretch` style property applies to widgets in a panel with\nflow layout. For example, `{stretch: 'horizontal'}` means the widget will\nexpand to fill available horizontal space within the panel. In the previous example,\nchange the flow layout type to `'horizontal'` to see the buttons arranged\nin a row instead of a column.\n\nIn a horizontal flow panel, a horizontally stretched widget expands to fill the space\navailable after all other widgets have taken up their natural *widths* . If more\nthan one widget is stretched horizontally, then the available horizontal space is\nsplit among them. A vertically stretched widget expands to fill the *height*\nof the panel.\n\nIn a vertical flow panel, a vertically stretched widget expands to fill the space\navailable after all other widgets have taken up their natural *heights* . If\nmore than one widget is stretched vertically, then the available vertical space is\nsplit among them. A horizontally stretched widget expands to fill the *width*\nof the panel.\n\n### Absolute\n\nAn absolute layout positions widgets according to positions in the panel. Unlike the\nflow layout, the position of a widget is determined by the `position` property\nof the widget's `style` property, not the order in which it is added to\nthe panel. The following example demonstrates using the `root.ui` panel with\nan absolute layout (the root panel's layout is a horizontal flow by default, but can be\nset with `ui.root.setLayout()`):\n\n### Code Editor (JavaScript)\n\n```javascript\nui.root.clear();\nui.root.setLayout(ui.Panel.Layout.absolute());\n\n// A function to make buttons labeled by position.\nfunction makeButton(position) {\n return ui.Button({\n label: position,\n style: {position: position}\n });\n}\n\n// Add labeled buttons to the panel.\nui.root.add(makeButton('top-left'));\nui.root.add(makeButton('top-center'));\nui.root.add(makeButton('top-right'));\nui.root.add(makeButton('middle-left'));\nui.root.add(makeButton('middle-right'));\nui.root.add(makeButton('bottom-left'));\nui.root.add(makeButton('bottom-center'));\nui.root.add(makeButton('bottom-right'));\n```\n\nThe absolute layout panel should look something like:\n\n`widgets()`\n-----------\n\nWhen you add a widget to a panel, it adds the widget to the panel's list of\nwidgets. Calling `widgets()` on the panel returns the\n`ui.data.ActiveList` which you can use to manipulate the widgets in the\npanel. Consider the following example, which adds widgets to a panel, adds the panel\nto the root panel, then updates a chart when the user clicks on the map:\n\n### Code Editor (JavaScript)\n\n```javascript\n// Load and display NDVI data.\nvar ndvi = ee.ImageCollection('NOAA/VIIRS/001/VNP13A1')\n .filterDate('2021-01-01', '2022-01-01').select('NDVI');\nMap.addLayer(\n ndvi.median(), {min: 0, max: 10000, palette: ['99c199', '006400']}, 'NDVI');\n\n// Configure the map.\nMap.setCenter(-94.84497, 39.01918, 8);\nMap.style().set('cursor', 'crosshair');\n\n// Create an empty panel in which to arrange widgets.\n// The layout is vertical flow by default.\nvar panel = ui.Panel({style: {width: '400px'}})\n .add(ui.Label('Click on the map'));\n\n// Set a callback function for when the user clicks the map.\nMap.onClick(function(coords) {\n // Create or update the location label (the second widget in the panel)\n var location = 'lon: ' + coords.lon.toFixed(2) + ' ' +\n 'lat: ' + coords.lat.toFixed(2);\n panel.widgets().set(1, ui.Label(location));\n\n // Add a red dot to the map where the user clicked.\n var point = ee.Geometry.Point(coords.lon, coords.lat);\n Map.layers().set(1, ui.Map.Layer(point, {color: 'FF0000'}));\n\n // Create a chart of NDVI over time.\n var chart = ui.Chart.image.series(ndvi, point, ee.Reducer.mean(), 200)\n .setOptions({\n title: 'NDVI Over Time',\n vAxis: {title: 'NDVI'},\n lineWidth: 1,\n pointSize: 3,\n });\n\n // Add (or replace) the third widget in the panel by\n // manipulating the widgets list.\n panel.widgets().set(2, chart);\n});\n\n// Add the panel to the ui.root.\nui.root.add(panel);\n```\n\nIn this example, observe that first, widgets are added to panel using\n`add()`. In the callback function registered to map clicks, `panel`'s\nlist of widgets is modified instead. Specifically, the third widget (which may or may\nnot exist) is set such that a new chart is displayed of NDVI over time. Learn more about\nevent handling functions on the [Events page](/earth-engine/guides/ui_events)."]]
