NativeScript/packages/core/ui/content-view/index.ts

import { View, CustomLayoutView, AddChildFromBuilder } from '../core/view';
import { layout } from '../../utils';

/**
 * Represents a View that has a single child - content.
 * The View itself does not have visual representation and serves as a placeholder for its content in the logical tree.
 */
export class ContentView extends CustomLayoutView implements AddChildFromBuilder {
	private _content: View;

	/**
	 * Gets or sets the single child of the view.
	 */
	get content(): View {
		return this._content;
	}
	set content(value: View) {
		const oldView = this._content;
		if (this._content) {
			this._removeView(this._content);
		}

		this._content = value;

		if (this._content) {
			this._addView(this._content);
		}

		this._onContentChanged(oldView, value);
		if (__APPLE__ && oldView !== value) {
			this.requestLayout();
		}
	}

	get layoutView(): View {
		let result: View;

		if (this._content) {
			let first = true;
			this._content._eachLayoutView((child) => {
				if (first) {
					first = false;
					result = child;
				} else {
					throw new Error('More than one layout child inside a ContentView');
				}
			});
		}

		return result;
	}

	get _childrenCount(): number {
		return this._content ? 1 : 0;
	}

	//@private
	/**
	 * Called when the content property has changed.
	 * @private
	 * @param oldView The previous content.
	 * @param newView The new content.
	 */
	public _onContentChanged(oldView: View, newView: View) {
		//
	}

	public _addChildFromBuilder(name: string, value: any) {
		if (value instanceof View) {
			this.content = value;
		}
	}

	public eachChildView(callback: (child: View) => boolean) {
		const content = this._content;
		if (content) {
			callback(content);
		}
	}

	// This method won't be called in Android because we use the native android layout.
	public onMeasure(widthMeasureSpec: number, heightMeasureSpec: number): void {
		const result = View.measureChild(this, this.layoutView, widthMeasureSpec, heightMeasureSpec);

		const width = layout.getMeasureSpecSize(widthMeasureSpec);
		const widthMode = layout.getMeasureSpecMode(widthMeasureSpec);

		const height = layout.getMeasureSpecSize(heightMeasureSpec);
		const heightMode = layout.getMeasureSpecMode(heightMeasureSpec);

		const measureWidth = Math.max(result.measuredWidth, this.effectiveMinWidth);
		const measureHeight = Math.max(result.measuredHeight, this.effectiveMinHeight);

		const widthAndState = View.resolveSizeAndState(measureWidth, width, widthMode, 0);
		const heightAndState = View.resolveSizeAndState(measureHeight, height, heightMode, 0);

		this.setMeasuredDimension(widthAndState, heightAndState);
	}

	// This method won't be called in Android because we use the native android layout.
	public onLayout(left: number, top: number, right: number, bottom: number): void {
		View.layoutChild(this, this.layoutView, 0, 0, right - left, bottom - top);
	}
}

ContentView.prototype.recycleNativeView = 'auto';