如何在 Android WebView 的 Web 应用程序端使用 backpress 事件？

Question

使用 JS 接口开发 Kotlin WebView，我的 Web 应用程序需要从本机端检测 KeyEvent.KEYCODE_BACK 事件，以便在呈现时关闭 Web 应用程序对话框。如果对话框被关闭，我应该在本机端什么也不做（return true to super），否则我需要完成 web view activity（return false to super）。为了理解我的意图，请阅读下面的代码，我在我的自定义 WebView 上实现了一个线索，

override fun onKeyDown(keyCode: Int, event: KeyEvent): Boolean {

    if (event.action == KeyEvent.ACTION_DOWN) {
        when (keyCode) {
            KeyEvent.KEYCODE_BACK -> {

                this.evaluateJavascript("onDeviceBackPressed();", ValueCallback {
                    if (it == "1") {
                        // "Web app consumed onDeviceBackPressed event!"
                    } else {
                        // "Web app did not consume onDeviceBackPressed event!"
                        // super.onKeyDown(keyCode, event) won't work
                    }
                })

                // I am required to make the return call wait
                // return true/false base on status returned by js func
            }
        }
    }
    return super.onKeyDown(keyCode, event)
}

但我知道异步等待超级调用是不可能的。我该如何以其他方式处理这种情况？

Answer 1

您可以在等待 JS 时在第一次按下事件期间使用 KeyEvent，然后在获得结果时 re-use 使用它。

我曾经对触摸事件使用过这样的技巧，所以它应该可以工作。

var delayedKeyCode : Int? = null
var delayedKeyEvent : KeyEvent? = null
var keyDownJSResult : String? = null

override fun onKeyDown(keyCode: Int, event: KeyEvent): Boolean {
    if (event.action == KeyEvent.ACTION_DOWN) {
        when (keyCode) {
            KeyEvent.KEYCODE_BACK -> {
                // see if there's "result" provided from JS
                keyDownJSResult?.let{
                    keyDownJSResult = null    // wipe out result so it's not triggered twice
                    if (it == "1") {
                        // "Web app consumed onDeviceBackPressed event!"
                        return true
                    } else {
                        // "Web app did not consume onDeviceBackPressed event!"
                        return super.onKeyDown(keyCode, event)
                    }
                }
                // otherwise store keyDown arguments for later and trigger JS
                delayedKeyCode = keyCode
                delayedKeyEvent = event
                this.evaluateJavascript("onDeviceBackPressed();", ValueCallback {
                     // when JS returns value, trigger this onKeyDown event again
                     val oldCode = delayedKeyCode
                     val oldEv = delayedKeyEvent
                     delayedKeyCode = null
                     delayedKeyEvent = null
                     keyDownJSResult = it
                     onKeyDown(oldCode, oldEv)
                })
                // always consume event when waiting for JS result
                return true 
            }
        }
    }
    return super.onKeyDown(keyCode, event)
}

Answer 2

终于，我的一个小技巧解决了我的问题，

override fun onKeyDown(keyCode: Int, event: KeyEvent): Boolean {

    if (event.action == KeyEvent.ACTION_DOWN) {
        when (keyCode) {
            KeyEvent.KEYCODE_BACK -> {
                this.evaluateJavascript("onDeviceBackPressed();", ValueCallback {
                    if (it == "1") {
                        // consumed by web app, do nothing
                    } else {
                        // not consumed by web app, fire explicit back press event
                        mContext.onBackPressed()
                    }
                })
                return true
            }
        }
    }
    return super.onKeyDown(keyCode, event)
}

如何在 Android WebView 的 Web 应用程序端使用 backpress 事件？

How to consume backpress events in web app side in Android WebView?

javascript

android

web-applications

webview

kotlin