Android Webview，为什么会调用onReceivedError？

Question

First, the code I tested is

class MainActivity : AppCompatActivity() {

companion object {
    private const val LOG_TAG = "WebView"
}

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

    webview.loadUrl("https://abc.xyz/investor/")

    webview.webViewClient = MyClient()
    webview.webChromeClient = WebChromeClient()
    webview.setDownloadListener { url, userAgent, contentDisposition, mimeType, contentLength ->
        Log.d(LOG_TAG, "onDownloadStart $url")
    }

}

class MyClient : WebViewClient() {
    override fun shouldOverrideUrlLoading(view: WebView?, url: String?): Boolean {
        Log.d(LOG_TAG, "shouldOverrideUrlLoading $url")
        view?.loadUrl(url)
        return true
    }

    @TargetApi(Build.VERSION_CODES.N)
    override fun shouldOverrideUrlLoading(view: WebView?, request: WebResourceRequest?): Boolean {
        Log.d(LOG_TAG, "shouldOverrideUrlLoading WRR")
        return shouldOverrideUrlLoading(view, request?.url.toString())
    }

    override fun onReceivedError(view: WebView?, errorCode: Int, description: String?, failingUrl: String?) {
        Log.d(LOG_TAG, "onReceivedError $errorCode $failingUrl")
        super.onReceivedError(view, errorCode, description, failingUrl)
    }

    override fun onReceivedError(view: WebView?, request: WebResourceRequest?, error: WebResourceError?) {
        Log.d(LOG_TAG, "onReceivedError WRR")
        super.onReceivedError(view, request, error)
    }

    override fun onPageFinished(view: WebView?, url: String?) {
        Log.d(LOG_TAG, "onPageFinished $url")
        super.onPageFinished(view, url)
    }

    override fun onPageStarted(view: WebView?, url: String?, favicon: Bitmap?) {
        Log.d(LOG_TAG, "onPageStarted $url")
        super.onPageStarted(view, url, favicon)
    }

    override fun onLoadResource(view: WebView?, url: String?) {
        Log.d(LOG_TAG, "onLoadResource $url")
        super.onLoadResource(view, url)
    }
}

}

Simply load the alphabet company homepage, and then try to download the PDF file.

Then you will see log like below

1. shouldOverrideUrlLoading
2. shouldInterceptRequest
3. onLoadResource
4. onDownloadStart
5. onPageStarted
6. onReceivedError
7. onPageFinished

The site is healthy and the download URL is fine.

But, why is onReceivedError call?

The error code is -1 ERROR_UNKNOWN And the tested version of Android Chrome is 78.0.3904.96.

Answer 1

this error is Report web resource loading error to the host application. These errors usually indicate inability to connect to the server. Note that unlike the deprecated version of the callback, the new version will be called for any resource (iframe, image, etc.), not just for the main page. Thus, it is recommended to perform the minimum required work in this callback.

you should go through developer documentation:

https://developer.android.com/reference/android/webkit/WebViewClient.html#onReceivedError(android.webkit.WebView,%20android.webkit.WebResourceRequest,%20android.webkit.WebResourceError)

u have to implemented permission in Application Manifest

    <uses-permission android:name="android.permission.INTERNET" />
    <uses-permission android:name="android.permission.WRITE_EXTERNAL_STORAGE" />
    <uses-permission android:name="android.permission.WAKE_LOCK" />

also,you should check permission inactivity

if (checkSelfPermission(android.Manifest.permission.WRITE_EXTERNAL_STORAGE) == PackageManager.PERMISSION_GRANTED) 
    {
     Log.v(TAG,"Permission is granted");
     //File write logic here
     return true;
    }`

If not, you need to ask the user to grant your app a permission:

ActivityCompat.requestPermissions(this, new String[]{Manifest.permission.WRITE_EXTERNAL_STORAGE}, REQUEST_CODE);