无法通过ID获取ImageView

Question

I want to show a splash screen until the app finishes loading the URL.
After searching, I found a solution - Splash screen while loading a url in a webview in android app

But I'm unable to implement it on my current code. I'm getting an error message while trying to get the splash image view by id.

Here is my code:

public class MyAppWebViewClient extends WebViewClient {

    private final Context context;

    public MyAppWebViewClient(Context context) {
        this.context = context;
    }

    @Override
    public boolean shouldOverrideUrlLoading(WebView view, String url) {

        if (url.contains("?dl=1")) {
            Uri source = Uri.parse(url);
            // Make a new request pointing to the download url
            DownloadManager.Request request = new DownloadManager.Request(source);
            if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.HONEYCOMB) {
                request.allowScanningByMediaScanner();
                request.setNotificationVisibility(DownloadManager.Request.VISIBILITY_VISIBLE_NOTIFY_COMPLETED);
            }

            String fileExtension = MimeTypeMap.getFileExtensionFromUrl(url);
            String fileName = URLUtil.guessFileName(url, null, fileExtension);

            // save the file in the "Downloads" folder of SDCARD
            request.setDestinationInExternalPublicDir(Environment.DIRECTORY_DOWNLOADS, fileName);
            // get download service and enqueue file
            DownloadManager manager = (DownloadManager) context.getSystemService(Context.DOWNLOAD_SERVICE);
            manager.enqueue(request);
            return true;
        }



        if (Uri.parse(url).getHost().contains("www.example.com")) {
            return false;
        }

        Intent intent = new Intent(Intent.ACTION_VIEW, Uri.parse(url));
        view.getContext().startActivity(intent);
        return true;
    }

    @Override
    public void onReceivedError(WebView view, int errorCode, String description, String failingUrl) {
        view.loadUrl("file:///android_asset/offline.html");
    }

    @Override
    public void onPageFinished(WebView view, String url) {
        //hide loading image
        myImageView = (ImageView) findViewById(R.id.activity_splash_logo).setVisibility(View.GONE);
        //show webview
        view.findViewById(R.id.activity_main_webview).setVisibility(View.VISIBLE);
    }

}

and activity.xml

<?xml version="1.0" encoding="utf-8"?>
<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:tools="http://schemas.android.com/tools"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    tools:context="com.myapp.MainActivity">

    <WebView
        android:id="@+id/activity_main_webview"
        android:layout_width="match_parent"
        android:layout_height="match_parent"
        android:visibility="gone"/>
    <ImageView
        android:id="@+id/activity_splash_logo"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_centerInParent="true"
        android:src="@mipmap/splash_logo"
        android:visibility="visible"
        />
</RelativeLayout>

The problem occuring in this line :

myImageView = (ImageView) findViewById(R.id.activity_splash_logo).setVisibility(View.GONE);

mainactivity.java

package com.myapp;

import android.Manifest;
import android.content.pm.PackageManager;
import android.os.Bundle;
import android.support.v4.app.ActivityCompat;
import android.support.v7.app.AppCompatActivity;
import android.webkit.WebSettings;
import android.webkit.WebView;

public class MainActivity extends AppCompatActivity {

    private static final int REQUEST_WRITE_EXTERNAL_STORAGE = 0;
    private WebView mWebView;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);

        mWebView = (WebView) findViewById(R.id.activity_main_webview);

        // Stop local links and redirects from opening in browser instead of WebView
        mWebView.setWebViewClient(new MyAppWebViewClient(MainActivity.this));

        mWebView.loadUrl("http://www.example.com/");

        // Enable Javascript
        WebSettings webSettings = mWebView.getSettings();
        webSettings.setJavaScriptEnabled(true);


        // Request required permission
        if (ActivityCompat.checkSelfPermission(this, Manifest.permission.WRITE_EXTERNAL_STORAGE)
                != PackageManager.PERMISSION_GRANTED) {
            ActivityCompat.requestPermissions(this,
                    new String[]{Manifest.permission.WRITE_EXTERNAL_STORAGE},
                    REQUEST_WRITE_EXTERNAL_STORAGE);
        }

        // Add user agent suffix
        this.mWebView.getSettings().setUserAgentString(
                this.mWebView.getSettings().getUserAgentString()
                        + " "
                        + BuildConfig.APPLICATION_ID
                        + "/"
                        + BuildConfig.VERSION_CODE
        );
    }

    // Prevent the back-button from closing the app
    @Override
    public void onBackPressed() {
        if (mWebView.canGoBack()) {
            mWebView.goBack();
        } else {
            super.onBackPressed();
        }
    }

}

Answer 1

Your encompassing class is not a Activity . There is no findViewbyId() in WebViewClient class.

Answer 2

You need to implement the onPageFinished within the Activity class if you want to use findViewById .

Also, if you don't need a reference to the splash image, then don't keep one.

mWebView = (WebView) findViewById(R.id.activity_main_webview);

mWebView.setWebViewClient(new MyAppWebViewClient(MainActivity.this) {

    @Override
    public void onPageFinished(WebView view, String url) {
        //hide loading image
        findViewById(R.id.activity_splash_logo).setVisibility(View.GONE);
        //show webview
        mWebView.setVisibility(View.VISIBLE);
    }
});

mWebView.loadUrl("http://www.example.com/");

Answer 3

Split this line

myImageView = (ImageView) findViewById(R.id.activity_splash_logo).setVisibility(View.GONE);

into two separate statements

myImageView = (ImageView) findViewById(R.id.activity_splash_logo);
myImageView.setVisibility(View.GONE);

Answer 4

You can't use findViewById with any view context. As you don't have any View reference.

You must init or call findViewById, wherever you are calling or initiating below code.

WebView myWebView = (WebView) findViewById(R.id.webview);
myWebView.setWebViewClient(new MyWebViewClient());

Initiate this also

myImageView = (ImageView) findViewById(R.id.activity_splash_logo);

Answer 5

Try:

ImageView myImageView = 
        (ImageView) findViewById(R.id.activity_splash_logo).setVisibility(View.GONE);