按下音量按钮时出现此错误答案

【问题标题】：I am getting this error on pressing volume button按下音量按钮时出现此错误
【发布时间】：2019-07-01 07:17:25
【问题描述】：

我创建了一个 webview 应用程序。按音量键时，我的应用程序崩溃。这是logcat中的错误

W/ViewRootImpl[MainActivity]：由于没有窗口焦点而取消事件： KeyEvent { action=ACTION_UP, keyCode=KEYCODE_VOLUME_DOWN, 扫描代码=114，元状态=0，标志=0x28，重复计数=0， eventTime=196583031, downTime=196582864, deviceId=9, source=0x101 }

下面是我的 MainActivity.java 文件：

package app.freeairdrop.io;

import android.annotation.SuppressLint;
import android.app.Activity;
import android.content.Intent;
import android.graphics.Bitmap;
import android.net.Uri;
import android.os.Bundle;
import android.support.v4.widget.SwipeRefreshLayout;
import android.view.KeyEvent;
import android.view.Menu;
import android.view.View;
import android.webkit.WebChromeClient;
import android.webkit.WebSettings;
import android.webkit.WebView;
import android.webkit.WebViewClient;
import android.widget.ProgressBar;
public class MainActivity extends Activity{
    private ProgressBar progressBar;
    private WebView webView;
    private SwipeRefreshLayout mySwipeRefreshLayout;
    @SuppressLint("SetJavaScriptEnabled")
    @Override
    public void onCreate(Bundle savedInstanceState) {




        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        progressBar = (ProgressBar) findViewById(R.id.progressBar);
        progressBar.setMax(100);
        webView = (WebView) findViewById(R.id.webView);
        webView.setWebViewClient(new WebViewClientDemo());
        webView.setWebChromeClient(new WebChromeClientDemo());
        webView.getSettings().setJavaScriptEnabled(true);

        webView.getSettings().setJavaScriptCanOpenWindowsAutomatically(true);
        webView.getSettings().setPluginState(WebSettings.PluginState.ON);
        webView.getSettings().setMediaPlaybackRequiresUserGesture(false);

        webView.loadUrl("http://freeairdrop.io/");

        mySwipeRefreshLayout = (SwipeRefreshLayout)this.findViewById(R.id.swipeContainer);


        mySwipeRefreshLayout.setOnRefreshListener(
                new SwipeRefreshLayout.OnRefreshListener() {
                    @Override
                    public void onRefresh() {
                        webView.reload();
                        mySwipeRefreshLayout.setRefreshing(false);
                    }
                }
        );

    }






    private class WebViewClientDemo extends WebViewClient {
        @Override
        public boolean shouldOverrideUrlLoading(WebView view, String url) {
            Uri uri = Uri.parse(url);
            if (uri.getHost() != null && (url.startsWith("https://freeairdrop.io/") || url.startsWith("https://www.freeairdrop.io/"))) {
                return false;
            }

            Intent intent = new Intent(Intent.ACTION_VIEW, Uri.parse(url));
            view.getContext().startActivity(intent);
            return true;
        }
        @Override
        public void onPageFinished(WebView view, String url) {
            super.onPageFinished(view, url);
            progressBar.setVisibility(View.GONE);
            progressBar.setProgress(100);
        }

        @Override
        public void onPageStarted(WebView view, String url, Bitmap favicon) {
            super.onPageStarted(view, url, favicon);
            progressBar.setVisibility(View.VISIBLE);
            progressBar.setProgress(0);
        }
    }


    private class WebChromeClientDemo extends WebChromeClient {
        public void onProgressChanged(WebView view, int progress) {
            progressBar.setProgress(progress);
        }
    }
    @Override
    public boolean onKeyDown(int keyCode, KeyEvent event) {
        if ((keyCode == KeyEvent.KEYCODE_BACK) && webView.canGoBack()) {
            webView.goBack();
            return true;
        }
        else {
            finish();
        }
        return super.onKeyDown(keyCode, event);
    }




    @Override
    public boolean onCreateOptionsMenu(Menu menu) {
        return true;
    }

    @Override
    // This method is used to detect back button
    public void onBackPressed() {
        if(webView.canGoBack()) {
            webView.goBack();
        } else {
            // Let the system handle the back button
            super.onBackPressed();
        }
    }
}

【问题讨论】：

您可以在问题中发布您的 MainActivity 代码吗？
显示触发此错误的代码。
添加了 MainActivity 文件@Zachary

标签： android android-webview

【解决方案1】：

Remove 
finish();

from here :
if ((keyCode == KeyEvent.KEYCODE_BACK) && webView.canGoBack()) {
            webView.goBack();
            return true;
        }
        else {
            finish();
        }

【讨论】：

【解决方案2】：

使用以下方法将焦点添加到 webview：

<WebView android:id="@+id/webview"
    android:layout_weight="1"
    android:layout_width="fill_parent"
    android:layout_height="fill_parent"
    android:focusable="true"/>

或者

webview.requestFocus(View.FOCUS_DOWN|View.FOCUS_UP);

【讨论】：

【解决方案3】：

从这里移除对 finish() 的调用，

@Override
public boolean onKeyDown(int keyCode, KeyEvent event) {
    if ((keyCode == KeyEvent.KEYCODE_BACK) && webView.canGoBack()) {
        webView.goBack();
        return true;
    }
    else {
        finish(); // Remove this, onBackPressed() should handle it.
    }
    return super.onKeyDown(keyCode, event);
}

【讨论】：