libgdx中弹框组件如何阻止事件穿透到下层组件

Background-背景说明

项目组中反馈说,自己定制了一个libgdx的Dialog,但是出现事件会穿透到底层组件的问题;
借此稍微看了下,libgdx以及scene2d的事件机制

所以这篇文章的内容包括以下几点:

• libgdx的事件简介
• scene2d/stage事件处理机制
• 阻止事件穿透的两个核心点
• scene2d/window组件的实现举例

libgdx的事件简介

不同平台有不同的输入设备,以及不同设备之间支持的输入属性是不同的;
通常来说: 桌面用户通过键盘和鼠标;安卓用户通过触摸屏,还会有一些额外的硬件设备支持,如:陀螺仪等;

libgdx 抽象了上述的输入设备,鼠标和触摸被一致处理,通常这样做满足大多数的应用,不过也会造成一些问题: 如无法识别多指触摸

InputProcessor事件回调

libgdx会把系统的事件处理,统一回调 InputProcessor 接口

public class InputAdapter implements InputProcessor {
	public boolean keyDown (int keycode) {
		return false;
	}

	public boolean keyUp (int keycode) {
		return false;
	}

	public boolean keyTyped (char character) {
		return false;
	}

	public boolean touchDown (int screenX, int screenY, int pointer, int button) {
		return false;
	}

	public boolean touchUp (int screenX, int screenY, int pointer, int button) {
		return false;
	}

	public boolean touchDragged (int screenX, int screenY, int pointer) {
		return false;
	}

	@Override
	public boolean mouseMoved (int screenX, int screenY) {
		return false;
	}

	@Override
	public boolean scrolled (int amount) {
		return false;
	}
}

多个输入事件处理器

有时候应用会需要多个输入事件处理器,如:先分发给UI事件处理器,然后再给应用的世界处理器

可以通过 InputMultiplexer实现

InputMultiplexer multiplexer = new InputMultiplexer();
multiplexer.addProcessor(new MyUiInputProcessor());
multiplexer.addProcessor(new MyGameInputProcessor());
Gdx.input.setInputProcessor(multiplexer);

InputMultiplexer 维护一个 事件处理器列表,所有新的事件需要处理时,按照列表依次分发

重点: 如果当前事件处理器返回true时,表明该事件已处理完成,不需要分发给后续的事件处理器

scene2d/stage事件处理机制

scene2d/stage 在libgdx 事件上,另外再加了一层逻辑,主要是实现了事件在组件链上的传递
事件传播分为两个阶段:
首先是capture,从root 到 target ,在这阶段,父节点可以预处理事件或者取消事件等;
然后是normal,从 target 返回 root

主要在Actor的fire方法中实现

public boolean fire (Event event) {
		if (event.getStage() == null) event.setStage(getStage());
		event.setTarget(this);

		// 收集所有的父级组件
		Array<Group> ancestors = Pools.obtain(Array.class);
		Group parent = this.parent;
		while (parent != null) {
			ancestors.add(parent);
			parent = parent.parent;
		}

		try {
			// 所有父级,从root开始到 Actor 逐级处理 capture listeners
			Object[] ancestorsArray = ancestors.items;
			for (int i = ancestors.size - 1; i >= 0; i--) {
				Group currentTarget = (Group)ancestorsArray[i];
				currentTarget.notify(event, true);
				if (event.isStopped()) return event.isCancelled();
			}

			// Notify the target capture listeners.
			notify(event, true);
			if (event.isStopped()) return event.isCancelled();

			// Notify the target listeners.
			notify(event, false);
			if (!event.getBubbles()) return event.isCancelled();
			if (event.isStopped()) return event.isCancelled();

			// 第二阶段,逐级冒泡到root, 处理 所有 的listeners
			for (int i = 0, n = ancestors.size; i < n; i++) {
				((Group)ancestorsArray[i]).notify(event, false);
				if (event.isStopped()) return event.isCancelled();
			}

			return event.isCancelled();
		} finally {
			ancestors.clear();
			Pools.free(ancestors);
		}
	}

阻止事件穿透的两个核心点

所以要阻止事件的传播,需要满足以下两个条件

• 要能捕获到事件,也就是说作为Event的target或者作为父级组件的 capture listeners

• 对应事件返回True 或者stop,阻止事件继续传递

作为Event的target就需要实现 Actor的hit检测:

	/** Returns the deepest {@link #isVisible() visible} (and optionally, {@link #getTouchable() touchable}) actor that contains
	 * the specified point, or null if no actor was hit. The point is specified in the actor's local coordinate system (0,0 is the
	 * bottom left of the actor and width,height is the upper right).
	 * <p>
	 * This method is used to delegate touchDown, mouse, and enter/exit events. If this method returns null, those events will not
	 * occur on this Actor.
	 * <p>
	 * The default implementation returns this actor if the point is within this actor's bounds and this actor is visible.
	 * @param touchable If true, hit detection will respect the {@link #setTouchable(Touchable) touchability}.
	 * @see Touchable */
	public Actor hit (float x, float y, boolean touchable) {
		if (touchable && this.touchable != Touchable.enabled) return null;
		if (!isVisible()) return null;
		return x >= 0 && x < width && y >= 0 && y < height ? this : null;
	}

scene2d/window组件的实现举例

window 是table子类,实现了拖拽和模态弹框
当设置了 isModal 属性时,就能够防止弹框底层的事件穿透

主要是两块内容:

• hit函数

	public Actor hit (float x, float y, boolean touchable) {
		if (!isVisible()) return null;
		Actor hit = super.hit(x, y, touchable);
		if (hit == null && isModal && (!touchable || getTouchable() == Touchable.enabled)) return this;
		float height = getHeight();
		if (hit == null || hit == this) return hit;
		if (y <= height && y >= height - getPadTop() && x >= 0 && x <= getWidth()) {
			// Hit the title bar, don't use the hit child if it is in the Window's table.
			Actor current = hit;
			while (current.getParent() != this)
				current = current.getParent();
			if (getCell(current) != null) return this;
		}
		return hit;
	}

• 返回相应事件为True

		addListener(new InputListener() {
			float startX, startY, lastX, lastY;

			public boolean touchDown (InputEvent event, float x, float y, int pointer, int button) {
        ...
				return edge != 0 || isModal;
			}

			public void touchUp (InputEvent event, float x, float y, int pointer, int button) {
				dragging = false;
			}

			public void touchDragged (InputEvent event, float x, float y, int pointer) {
				if (!dragging) return;
				...
				setBounds(Math.round(windowX), Math.round(windowY), Math.round(width), Math.round(height));
			}

			public boolean mouseMoved (InputEvent event, float x, float y) {
				updateEdge(x, y);
				return isModal;
			}

			public boolean scrolled (InputEvent event, float x, float y, int amount) {
				return isModal;
			}

			public boolean keyDown (InputEvent event, int keycode) {
				return isModal;
			}

			public boolean keyUp (InputEvent event, int keycode) {
				return isModal;
			}

			public boolean keyTyped (InputEvent event, char character) {
				return isModal;
			}
		});