如何在网页视图中加载缓存页面

Question

我在HTML页面上应用了缓存清单。

在 Chrome 浏览器上，当互联网连接断开时，它会重定向到缓存模式。好吧，Android-Webview并非如此。它给出以下错误：

无法加载网页

净：ERR_NAME_NOT_RESOLVED

已经浏览了各种资源，但似乎没有帮助。

以下是我使用的代码：

package com.example.page;
import android.app.Activity;
import android.app.ProgressDialog;
import android.content.Intent;
import android.content.SharedPreferences;
import android.content.pm.PackageManager;
import android.content.res.Configuration;
import android.graphics.Bitmap;
import android.net.Uri;
import android.os.Build;
import android.os.Bundle;
import android.preference.PreferenceManager;
import android.support.v4.app.ActivityCompat;
import android.support.v4.content.ContextCompat;
import android.view.View;
import android.webkit.ValueCallback;
import android.webkit.WebChromeClient;
import android.webkit.WebSettings;
import android.webkit.WebView;
import android.webkit.WebViewClient;
import android.widget.Toast;
import com.google.firebase.iid.FirebaseInstanceId;
public class MainActivity extends Activity {
    public static WebView mWebview;
    private android.content.Context Context;
    private static String getIntentValue = null;
    public static SharedPreferences sharedPreferences;
    private ProgressDialog mProgressDialog;
    private String mCM;
    private ValueCallback<Uri> mUM;
    private ValueCallback<Uri[]> mUMA;
    private final static int FCR=1;
    @Override
    protected void onActivityResult(int requestCode, int resultCode, Intent intent){
        super.onActivityResult(requestCode, resultCode, intent);
        mWebview.setWebViewClient(new Callback());
    }
    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        Context = this;
        String regId = FirebaseInstanceId.getInstance().getToken();
        getIntentValue = getIntent().getStringExtra("value");
        sharedPreferences = PreferenceManager.getDefaultSharedPreferences(this);
        if (!DetectConnection.checkInternetConnection(this)) {
            Toast.makeText(getApplicationContext(), "No Internet Connection!", Toast.LENGTH_LONG).show();
            finish(); //Calling this method to close this activity when internet is not available.
        } else {
            mWebview = (WebView) findViewById(R.id.webview1);
            WebSettings webSettings = mWebview.getSettings();
            mWebview.getSettings().setJavaScriptEnabled(true);
            mWebview.setWebChromeClient(new WebChromeClient());
            mWebview.setWebViewClient(new CustomWebViewClient());
            //improve WebView Performance
            mWebview.getSettings().setRenderPriority(WebSettings.RenderPriority.HIGH);
            mWebview.getSettings().setAppCacheEnabled(false);
            mWebview.getSettings().setCacheMode(WebSettings.LOAD_DEFAULT);

            if(Build.VERSION.SDK_INT >=23 && (ContextCompat.checkSelfPermission(this, android.Manifest.permission.WRITE_EXTERNAL_STORAGE) != PackageManager.PERMISSION_GRANTED || ContextCompat.checkSelfPermission(this, android.Manifest.permission.CAMERA) != PackageManager.PERMISSION_GRANTED)) {
                ActivityCompat.requestPermissions(MainActivity.this, new String[]{android.Manifest.permission.WRITE_EXTERNAL_STORAGE, android.Manifest.permission.CAMERA}, 1);
            }
            mWebview.setScrollBarStyle(View.SCROLLBARS_INSIDE_OVERLAY);
            webSettings.setDomStorageEnabled(true);
            webSettings.setLayoutAlgorithm(WebSettings.LayoutAlgorithm.NARROW_COLUMNS);
            webSettings.setUseWideViewPort(true);
            webSettings.setAllowFileAccess(true);
            webSettings.setSavePassword(true);
            webSettings.setSaveFormData(true);
            webSettings.setEnableSmoothTransition(true);
            // progress dialog
            mProgressDialog = new ProgressDialog(Context);
            if (sharedPreferences.getBoolean("isKeyGenerated", true)) {
                if (getIntentValue != null) {
                    mWebview.loadUrl("http://www.example.com/page");
                    getIntentValue = null;
                } else {
                    mWebview.loadUrl("http://www.example.com/page2");
                }
            }
        }

    }

    public class Callback extends WebViewClient{
        public void onReceivedError(WebView view, int errorCode, String description, String failingUrl){
            Toast.makeText(getApplicationContext(), "Failed loading app!", Toast.LENGTH_SHORT).show();
        }
    }

    // Function to load all URLs in same webview
    private class CustomWebViewClient extends WebViewClient {
        public boolean shouldOverrideUrlLoading(WebView view, String url) {
            if (url.contains(".pdf")) {
                Intent i = new Intent(Intent.ACTION_VIEW, Uri.parse(url));
                startActivity(i);
            } else {
                view.loadUrl(url);
            }
            return true;
        }
        @Override
        public void onPageStarted(WebView view, String url, Bitmap favicon) {
            // TODO Auto-generated method stub
            super.onPageStarted(view, url, favicon);
            //on page started, show loading page
            mProgressDialog.setCancelable(true);
            mProgressDialog.setProgressStyle(ProgressDialog.STYLE_SPINNER);
            mProgressDialog.show();
        }
        @Override
        public void onPageFinished(WebView view, String url)
        {
            String currentPage= mWebview.getUrl();
            SharedPreferences.Editor editor = sharedPreferences.edit();
            editor.putString("currentpage",currentPage);
            editor.commit();
            //after loading page, remove loading page
            // TODO Auto-generated method stub
            super.onPageFinished(view, url);
            mProgressDialog.dismiss();
        }
        @Override
        public void onReceivedError(WebView view, int errorCode,
                                    String description, String failingUrl) {
            view.loadUrl("http://example.com/page");
        }
    }
    @Override
    public void onBackPressed() {
        SharedPreferences sharedPreferences = PreferenceManager.getDefaultSharedPreferences(this);
        String currenturl = sharedPreferences.getString("currentpage", null);
        mWebview.requestFocus();
        if (currenturl.contains("http://example.com/page")){
            moveTaskToBack(true);
        }else{
            mWebview.goBack();
        }
        if (mWebview.canGoBack()) {
            if (!DetectConnection.checkInternetConnection(Context)) {
                Toast.makeText(Context, "No Internet Connection!", Toast.LENGTH_SHORT).show();
            }
        }
    }

    public static void loadUrl(String key) {
        if (getIntentValue != null) {
            mWebview.loadUrl("http://example.com/page");
            getIntentValue = null;
        } else {
            mWebview.loadUrl("http://example.com/page");
        }
    }

    public static void reLoad() {
        mWebview.reload();
    }
    @Override
    public void onConfigurationChanged(Configuration newConfig){
        super.onConfigurationChanged(newConfig);
    }
}

Answer 1

只需包含 enableHTML5AppCache((

private void enableHTML5AppCache() {
        mWebview.getSettings().setDomStorageEnabled(true);
        mWebview.getSettings().setAppCachePath("/data/data/" + getPackageName() + "/cache");
        mWebview.getSettings().setAppCacheEnabled(true);
        mWebview.getSettings().setCacheMode(WebSettings.LOAD_CACHE_ELSE_NETWORK);
    }

Answer 2

mWebview.getSettings().setCacheMode( WebSettings.LOAD_CACHE_ELSE_NETWORK)

这将告诉 WebView 从缓存加载页面，但如果它需要缓存中没有的任何内容，它会查看网络，当您没有连接时，它只会为您提供"无法加载页面错误"。这是因为遗憾的是，并非所有内容都存储在缓存中，即使使用此设置，您也会注意到浏览器使用网络。

使用WebSettings.LOAD_CACHE_ONLY

mWebview.getSettings().setCacheMode(WebSettings.LOAD_CACHE_ONLY);

Answer 3

更改此行：

mWebview.getSettings().setCacheMode(WebSettings.LOAD_DEFAULT);

自：

mWebview.getSettings().setCacheMode( WebSettings.LOAD_CACHE_ELSE_NETWORK)

Answer 4

2021 年更新情况发生了变化：已弃用应用程序缓存 API 已弃用，一旦在 Chromium 中删除支持，此方法将在所有 Android 版本上成为无操作。请考虑改用服务工作进程。有关详细信息，请参阅 https://web.dev/appcache-removal/。阅读有关服务工作者的信息，而不是:)快乐编码:P