Realization idea

====

By monitoring the state of the keyboard and the state of the commodity card, the translation y animation is made for the bullet screen area. The implementation idea is very simple. There are some difficulties below

• Implementation method of monitoring keyboard state

• How to get the height of the keyboard

Monitor keyboard pop-up and stow

========

Because Android can't monitor the keyboard, online solutions are judged indirectly by viewTreeObserver

view.viewTreeObserver.addOnGlobalLayoutListener {

	// Here, by judging the visible height of the screen, you can indirectly judge the pop-up and retraction

} 

Why can it be achieved in this way?

Let's take a look at when addOnGlobalLayoutListener was called back

Here, you need to understand the drawing process of View. The code is in line 2628 (API 29) of the ViewRootImpl class

if (triggerGlobalLayoutListener) {

    mAttachInfo.mRecomputeGlobalAttributes = false;

    mAttachInfo.mTreeObserver.dispatchOnGlobalLayout();

}

This callback will be triggered when a Window such as an Activity or Dialog completes the measurement and layout of the added layout. It can be inferred from this that the re layout of the Activity must be triggered when the keyboard pops up and retracts

Why does keyboard pop-up trigger the rearrangement of activities

Android provides the property of windowSoftInputMode for developers to configure the state of the keyboard and how the interface should adapt to the keyboard

// The current interface does not change. The keyboard is directly covered on the interface and will not be rearranged. Therefore, the GlobalLayoutListener callback will not be triggered

android:windowSoftInputMode="adjustNothing"



// Changing the size of the current layout to fit the keyboard will trigger the GlobalLayoutListener callback. This configuration is very suitable for the IM chat interface of wechat

android:windowSoftInputMode="adjustResize"



// Directly pushing the layout to the top will trigger the GlobalLayoutListener callback

android:windowSoftInputMode="adjustPan"



// By default, the interface can be swiped and will be set to adjustResize, otherwise adjustPan

android:windowSoftInputMode="adjustUnspecified"

The pop-up of the keyboard will change the interface layout, so you can judge whether the keyboard pops up in the above way

How to judge whether the keyboard pops up

The keyboard pop-up will change the visible area of the current Window. If the current visible height is less than the original height, we judge that the keyboard pops up

You can obtain the visible area of the Window where the View is located through the methods in the View

view.getWindowVisibleDisplayFrame(Rect)

Then the original height minus the current height is the height of the keyboard

RecyclerView top gradient vanishing effect

=====================

RecyclerView provides this attribute to achieve this effect (it's hard to know this attribute when doing the project). android:requiresFadingEdge = "vertical", but after setting this attribute, android:overScrollMode="never" has no effect, so RecyclerView is rewritten here

// android:overScrollMode="never" style

edgeEffectFactory = object : EdgeEffectFactory() {

    override fun createEdgeEffect(view: RecyclerView, direction: Int): EdgeEffect {

        return object : EdgeEffect(context) {

            override fun draw(canvas: Canvas): Boolean {

                return false

            }

        }

    }

}

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