react-native/Libraries/Utilities/Dimensions.js

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/**
* Copyright (c) 2015-present, Facebook, Inc.
* All rights reserved.
*
* This source code is licensed under the BSD-style license found in the
* LICENSE file in the root directory of this source tree. An additional grant
* of patent rights can be found in the PATENTS file in the same directory.
*
* @providesModule Dimensions
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* @flow
*/
'use strict';
var Platform = require('Platform');
var UIManager = require('UIManager');
var RCTDeviceEventEmitter = require('RCTDeviceEventEmitter');
var invariant = require('fbjs/lib/invariant');
var dimensions = {};
class Dimensions {
/**
* This should only be called from native code by sending the
* didUpdateDimensions event.
*
* @param {object} dims Simple string-keyed object of dimensions to set
*/
static set(dims: {[key:string]: any}): void {
// We calculate the window dimensions in JS so that we don't encounter loss of
// precision in transferring the dimensions (which could be non-integers) over
// the bridge.
if (dims && dims.windowPhysicalPixels) {
// parse/stringify => Clone hack
dims = JSON.parse(JSON.stringify(dims));
var windowPhysicalPixels = dims.windowPhysicalPixels;
dims.window = {
width: windowPhysicalPixels.width / windowPhysicalPixels.scale,
height: windowPhysicalPixels.height / windowPhysicalPixels.scale,
scale: windowPhysicalPixels.scale,
fontScale: windowPhysicalPixels.fontScale,
};
if (Platform.OS === 'android') {
// Screen and window dimensions are different on android
var screenPhysicalPixels = dims.screenPhysicalPixels;
dims.screen = {
width: screenPhysicalPixels.width / screenPhysicalPixels.scale,
height: screenPhysicalPixels.height / screenPhysicalPixels.scale,
scale: screenPhysicalPixels.scale,
fontScale: screenPhysicalPixels.fontScale,
};
// delete so no callers rely on this existing
delete dims.screenPhysicalPixels;
} else {
dims.screen = dims.window;
}
// delete so no callers rely on this existing
delete dims.windowPhysicalPixels;
}
Object.assign(dimensions, dims);
}
/**
* Initial dimensions are set before `runApplication` is called so they should
* be available before any other require's are run, but may be updated later.
*
* Note: Although dimensions are available immediately, they may change (e.g
* due to device rotation) so any rendering logic or styles that depend on
* these constants should try to call this function on every render, rather
* than caching the value (for example, using inline styles rather than
* setting a value in a `StyleSheet`).
*
* Example: `var {height, width} = Dimensions.get('window');`
*
* @param {string} dim Name of dimension as defined when calling `set`.
* @returns {Object?} Value for the dimension.
*/
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static get(dim: string): Object {
invariant(dimensions[dim], 'No dimension set for key ' + dim);
return dimensions[dim];
}
}
Dimensions.set(UIManager.Dimensions);
RCTDeviceEventEmitter.addListener('didUpdateDimensions', function(update) {
Dimensions.set(update);
});
module.exports = Dimensions;