从 ViewPager 中的缓存集加载 webview 数据

Question

我正在开发一个需要将 webView 设置为 ViewPager 项目的应用程序。我每次都使用创建片段的newInstace() 作为我拥有的URL 的arrayList 的大小来做到这一点。 但是，我有超过 20 个 URL 需要加载，所以如果我设置 mPager.setOffscreenPageLimit(myArray.size()) 会占用太多的负载。如果我使用mPager.setOffscreenPageLimit(1)，那么它每次都会重新加载。那么，有没有什么办法可以防止每次都重新加载网页呢？

public static class PlaceholderFragment extends BaseFragment {

    Activity activity;
    private int media_position = 0;
    private String media_url = "";

    private static final String KEY_CONTENT = "CategoriesFragment:Content";
    private String mContent = "???";

    public static PlaceholderFragment newInstance(int media_position, String media_url) {

        PlaceholderFragment fragment = new PlaceholderFragment();
        fragment.media_position = media_position;
        fragment.media_url = media_url;
        return fragment;
    }

    @Override
    public void onSaveInstanceState(Bundle outState) {
        super.onSaveInstanceState(outState);
        outState.putString(KEY_CONTENT, mContent);
    }

    @Override
    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        if ((savedInstanceState != null) && savedInstanceState.containsKey(KEY_CONTENT)) {
            mContent = savedInstanceState.getString(KEY_CONTENT);
        }
    }

    @Override
    public View onCreateView(LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState) {
        web1 = inflater.inflate(R.layout.fragment_main, container, false);
        activity = getActivity();

        mWebView1 = (WebView) web1.findViewById(R.id.webview);

        mWebView1.setWebViewClient(new WebViewClient());
        mWebView1.getSettings().setJavaScriptEnabled(true);
        mWebView1.getSettings().setJavaScriptCanOpenWindowsAutomatically(true);
        mWebView1.getSettings().setSupportMultipleWindows(true);
        mWebView1.getSettings().setSupportZoom(true);
        mWebView1.getSettings().setBuiltInZoomControls(false);
        mWebView1.getSettings().setAllowFileAccess(true);
        mWebView1.getSettings().setAppCacheEnabled(true);
        mWebView1.getSettings().setDomStorageEnabled(true);
        mWebView1.getSettings().setCacheMode(WebSettings.LOAD_CACHE_ELSE_NETWORK);

        mWebView1.setWebViewClient(new WebViewClient() {
            @Override
            public void onPageStarted(WebView view, String url, Bitmap favicon) {
                super.onPageStarted(view, url, favicon);

                boolean isLoaded = false;

                if (Utils.LoadedUrlList.containsKey(Utils.currentUrl)) {
                    Log.e("Matched key", "media_position --> " + media_position + " currentUrl --> " + Utils.currentUrl);
                    isLoaded = true;
                } else {
                    Log.e("Not Matched", "media_position --> " + media_position + " media_url --> " + media_url);
                    isLoaded = false;
                }

                Log.e("onPageStarted", "onPageStarted");

                if (!isLoaded)
                    if (media_position == 0)
                        ShowProgressDialog(activity, activity.getString(R.string.loading));
            }

            @Override
            public void onPageFinished(WebView view, String url) {
                super.onPageFinished(view, url);

                Log.e("onPageFinished", "onPageFinished");
                Log.e("onPageFinished", "--> " + url);

                hideProgressDialog();
                CookieSyncManager.getInstance().sync();

                for (int i = 0; i < Utils.SocialURLList.size(); i++) {

                    if (url.equals(Utils.SocialURLList.get(i))) {
                        Utils.LoadedUrlList.put(Utils.SocialURLList.get(0), true);
                    }
                }
            }
        });

        mWebView1.loadUrl(media_url);
        return web1;
    }

}

Answer 1

public void onPageFinished(WebView view, String url) {
    CookieSyncManager.getInstance().sync();
}

一旦加载了 WebView 并调用了 onPageFinished，您就可以将数据保存到 cookie 中。 还要加webView.getSettings().setCacheMode(WebSettings.LOAD_CACHE_ELSE_NETWORK);

Answer 2

我不得不做同样的事情。我发现将数据保存在onSaveInstanceState 并不能很好地扩展（我没有尝试@Ameer 建议的cookie 方法）。

相反，在您下载 HTML 后，您可以将 HTML 保存到这样的文件中：

    try {
        OutputStreamWriter outputStreamWriter =
                new OutputStreamWriter(context.openFileOutput(email_id + ".txt", Context.MODE_PRIVATE));
        outputStreamWriter.write(email_body);
        outputStreamWriter.close();
    } catch (IOException e) {
        Log.e("Exception", "File write failed: " + e.toString());
    }

并将email_id 与当前时间保存在SharedPreferences 中。

然后当片段再次加载时，检查email_id 是否存在于SharedPreferences 中。如果没有，或者使用它节省的时间超过您所需的缓存长度，则（重新）从网络加载页面。否则，像这样调用缓存的email_body

public String getCachedHTML(String email_id) {
    String ret = "";
    try {
        InputStream inputStream = context.openFileInput(email_id + ".txt");

        ret = readFile(ret, inputStream);
    } catch (FileNotFoundException e) {
        Log.e("login activity", "Email cache not found: " + e.toString());
    } catch (IOException e) {
        Log.e("login activity", "Can not read email cache: " + e.toString());
    }
    return ret;
}`

您可以像这样在 webview 上设置 HTML：

webView.loadData(email_body, "text/html; charset=UTF-8", null);