Kotlin: All WebView methods must be called on the same thread

Question

This is my kotlin code:

class WebAppInterface(private val mContext: Context, private val myWebView: WebView) {
    @JavascriptInterface
    fun goToHello() {
        val myWebView = myWebView
        myWebView.loadUrl("file:///android_asset/hello.html")
    }
}

class MainActivity : AppCompatActivity() {
    override fun onCreate(savedInstanceState: Bundle?) {
        super.onCreate(savedInstanceState)
        setContentView(R.layout.activity_main)

        val myWebView: WebView = findViewById(R.id.webview)
        myWebView.settings.javaScriptEnabled = true
        myWebView.addJavascriptInterface(WebAppInterface(this, myWebView), "Android")
        myWebView.loadUrl("file:///android_asset/index.html")
    }
}

But it's crash.

Caused by: java.lang.Throwable: A WebView method was called on thread 'JavaBridge'. All WebView methods must be called on the same thread.

How can I fix this? I found a solution by searching but this was java code. Kotlin and Java are compatible but did not run due to a syntax error. (I think it's because I don't know Kotlin and Java. Anyway)

I'm a JavaScript-based full stack developer and I don't have any Android knowledge so I only wanted to use webviews. But this is also very difficult for me. (It's like the period of chaos when I first learned JavaScript.)

Please tell me the solution. ps. If you have a good list of Kotlin's inheritance and scope concepts, please link.

Please try to comment `myWebView.loadUrl("file:///android_asset/hello.html")`from 'fun goToHello(...)' and print some log here and check if it crash or not. — Hello World, Mar 03 '20 at 04:54

score 9 · Accepted Answer · answered Mar 03 '20 at 05:00

9

You should use Runnable and Post to WebView Handler.

myWebView.post(Runnable {
   myWebView.loadUrl("file:///android_asset/index.html")
})

answered Mar 03 '20 at 05:00

Roman

2,464
2
17
21

Thank. You are my savior. The solution code shows how poor my kotlin knowledge is. – msm082919 Mar 03 '20 at 05:09
Mention not. We are team here. – Roman Mar 03 '20 at 06:39
`myWebView.post { myWebView.loadUrl("file:///android_asset/index.html") }` – Dr.jacky Apr 23 '21 at 12:38

Muhammad Mubeen · Answer 2 · 2020-03-03T05:27:31.207

2

Try This

mWebView.post(object:Runnable { 
public override fun run() { 
   mWebView.loadUrl("") 
   } 
})

edited Mar 03 '20 at 05:27

answered Mar 03 '20 at 05:09

Muhammad Mubeen

153
1
8

1

i have updated the code in kotlin,also you can convert java code to kotlin using *https://try.kotlinlang.org/* – Muhammad Mubeen Mar 03 '20 at 05:26

score 1 · Answer 3 · answered Mar 03 '20 at 05:10

As the link you posted here the problem is because

the JavaScript method is executed on a background (i.e. non-UI) thread. You need to call all Android View related methods on the UI thread. You can achieve what you need with:

The kotlin solution is the following

    val myWebView: WebView = findViewById(R.id.webview)
    //Apply webview's properties if it's not null
    myWebView?.run {
        settings.javaScriptEnabled = true
        addJavascriptInterface(WebAppInterface(this, myWebView), "Android")
        post {
            loadUrl("file:///android_asset/index.html")
        }
    }

As you can see here there a particular instruction here run this instruction is a part of the kotlin's scope functions.

Probably this tutorial that is designed for javascript developers might be helpul to kick start with kotlin https://dev.to/cassiozen/kotlin-for-js-devs-part-1-5bld

Really thanks a lot. It is very goooooooood * 999 link for me. — msm082919, Mar 03 '20 at 05:20

Kotlin: All WebView methods must be called on the same thread

3 Answers3