缓存 - android webview无法从缓存中正确加载css

Question

我已经使用缓存机制实现了webview，该机制在设备脱机时从缓存加载页面。但奇怪的是我得到了以下行为。

每当设备离线且app正在从缓存加载页面时，它看起来像预期的那样：

但下次我打开同一页面的webview时。它从缓存中呈现页面而不使用css：

序列继续其他时间.i.e首先是预期的页面，另一次是没有css的页面。我试图找到解决方案，但未能提出任何解决方案。有谁知道webview加载的奇怪行为的原因？

我的布局文件是：

<LinearLayout  xmlns:android="http://schemas.android.com/apk/res/android"

android:layout_width="fill_parent"
android:layout_height="fill_parent"
>
<FrameLayout
    android:id="@+id/webViewPlaceholder"
    android:layout_width="fill_parent"
    android:layout_height="fill_parent"></FrameLayout>

</LinearLayout>

我在framelayout中声明了webview：

  @Override
public void onCreate(Bundle savedInstanceState) {
 try {
     super.onCreate(savedInstanceState);
     if(Build.VERSION.SDK_INT>=21)    {
         WebView.enableSlowWholeDocumentDraw();
     }
     setContentView(R.layout.display_result);
     url = Uri.parse(getIntent().getStringExtra("Url"));

     initUI();
 }
 catch (Exception e)
 {
     Toast.makeText(DisplayResult.this, ""+e, Toast.LENGTH_SHORT).show();
 }
}


public void initUI()
{
try {
    webViewPlaceholder = (FrameLayout) findViewById(R.id.webViewPlaceholder);
    if (webView == null) {

        //webView = (WebView) findViewById(R.id.webview);
        webView = new WebView(this);


        // webView.getSettings().setLoadWithOverviewMode(true);
        webView.getSettings().setUseWideViewPort(true);
        webView.getSettings().setSupportZoom(true);
        webView.getSettings().setBuiltInZoomControls(true);
        webView.getSettings().setDisplayZoomControls(false);

        webView.getSettings().setAppCacheMaxSize( 5 * 1024 * 1024 ); // 5MB
        webView.getSettings().setAppCachePath(getApplicationContext().getCacheDir().getAbsolutePath());
        webView.getSettings().setAllowFileAccess(true);
        webView.getSettings().setAppCacheEnabled(true);
        webView.getSettings().setJavaScriptEnabled(true);
        webView.getSettings().setLayoutAlgorithm(WebSettings.LayoutAlgorithm.NORMAL);
        webView.getSettings().setCacheMode( WebSettings.LOAD_DEFAULT );

        webView.getSettings().setTextSize(WebSettings.TextSize.NORMAL);
        webView.getSettings().setTextZoom(0);
        webView.setWebViewClient(new Callback());

        if(!isConnectedToInternet())
        {

            webView.getSettings().setCacheMode( WebSettings.LOAD_CACHE_ELSE_NETWORK );

        }
        try {
            webView.loadUrl(url.toString());

        }
        catch(Exception e)
        {
            Toast.makeText(DisplayResult.this,""+e,Toast.LENGTH_LONG).show();
        }
    }

    webViewPlaceholder.addView(webView);
}
catch (Exception e)
{
    Toast.makeText(DisplayResult.this, ""+e, Toast.LENGTH_SHORT).show();
}
}

private class Callback extends WebViewClient {
    MaterialDialog m=null ;


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

        return false;
    }

    @Override
    public void onPageStarted(WebView view, String url, Bitmap facIcon) {

        //Toast.makeText(DisplayResult.this,"onload "+ (i++),Toast.LENGTH_SHORT).show();

        if(flag && m==null) {

            m = new MaterialDialog.Builder(DisplayResult.this)
                    .title("Fetching Result")
                    .content("Please wait...")
                    .progress(true, 0)

                    .show();


        }
    }
    @Override
    public void onPageFinished(WebView view, String url){
        super.onPageFinished(view,url);
        //Toast.makeText(DisplayResult.this,"onfinish",Toast.LENGTH_SHORT).show();
        if(flag || m!=null) {
            m.cancel();
            //Toast.makeText(DisplayResult.this, "canceled", Toast.LENGTH_SHORT).show();
        }
        i=1;

    }
@Override
    public void onReceivedError(WebView view, int errorCode, String description, String failingUrl) {
        try {
            //Toast.makeText(DisplayResult.this,"onerror",Toast.LENGTH_SHORT).show();

            new MaterialDialog.Builder(DisplayResult.this)
                    .title("Error ")
                    .content("No Internet Access")
                    .positiveText("OK")
                    .show();

            if (errorCode == -2) {

                String summary = "<html><body ><p style='color: red;'>Unable to load information. Please check if your network connection is working properly or try again later.</p></body></html>";
                view.loadData(summary, "text/html", null);


            }

        }
        catch (Exception e)
        {
            Toast.makeText(DisplayResult.this, ""+e, Toast.LENGTH_SHORT).show();
        }
    }


}

我的应用程序的Targetsdkversion是21.任何帮助将不胜感激。