除非在浏览器中打开，否则 Android webview 不会加载

Question

我制作了一个包含 webview 的应用程序，它会在 webview 开始加载 url 时检查连接。在 AVD 上运行良好，但当我在实际设备上测试时，出现了一个大错误。我假设 webview 没有加载，因为它显示的都是黑色的。不管我做什么，都是黑色的。在我弄清楚如何让它工作前 3 天，它首先需要在浏览器应用程序中查看目标 url，然后才能在我的应用程序上打开目标 url。最重要的是，除非您首先在浏览器中打开它，否则 webview 不会显示目标 url。我对此进行了研究，但我所能找到的只是关于如何在 web View 中打开不会打开浏览器的链接的答案。

这是我主要 Activity 的代码:

public class MainActivity extends Activity
{

private WebView wv;
private ProgressBar progress;
private static String mycaturl=" *target url* ";

@SuppressLint("NewApi")
@Override
protected void onCreate(Bundle savedInstanceState)
{
    super.onCreate(savedInstanceState);     
    StrictMode.ThreadPolicy policy = new StrictMode.ThreadPolicy.Builder().permitAll().build();
    StrictMode.setThreadPolicy(policy);
    if (reachable(this))
    {
        Toast.makeText(this, "Reachable", Toast.LENGTH_SHORT).show();
        buildwv( savedInstanceState, WebSettings.LOAD_DEFAULT );
    }
    else if (!reachable(this))
    {
        Toast.makeText(this, "Unreachable", Toast.LENGTH_SHORT).show();
        eolc( savedInstanceState );
    }
    else
    {
        Toast.makeText(this, "onCreate error.", Toast.LENGTH_SHORT).show();
        finish();
    }
}


@SuppressLint({ "SetJavaScriptEnabled" })
public void buildwv(Bundle sis, int load)
{
    setContentView(R.layout.activity_main);

    //assigning objects to variables
    wv=(WebView) findViewById(R.id.wv);
    wv.setWebViewClient( new wvc() );
    progress=(ProgressBar) findViewById(R.id.progress);

    //websettings
    WebSettings ws = wv.getSettings();
    ws.setAppCacheMaxSize( 100 * 1024 * 1024 ); // 100MB
    ws.setAppCachePath( this.getCacheDir().getAbsolutePath() );
    ws.setAllowFileAccess( true );
    ws.setAppCacheEnabled( true );
    ws.setJavaScriptEnabled( true );
    ws.setCacheMode(load);

    //if instance is saved, to catch orientation change
    if(sis==null)
    {   wv.loadUrl(mycaturl);   }
}


public void eolc(final Bundle sis)
{
    AlertDialog.Builder alertDialog = new AlertDialog.Builder( MainActivity.this );

    alertDialog.setTitle("ERROR 1");
    alertDialog.setMessage("Host is unreachable. Load from cache or exit.");
    alertDialog.setIcon(R.drawable.tick);

    alertDialog.setPositiveButton( "Load from Cache", new DialogInterface.OnClickListener()
    {
        public void onClick(DialogInterface dialog,int which)
        {
            // Write your code here to execute after dialog
            Toast.makeText(getApplicationContext(), "You chose to load cache.", Toast.LENGTH_SHORT).show();
            buildwv( sis, WebSettings.LOAD_CACHE_ELSE_NETWORK );
        }
    });

    alertDialog.setNeutralButton( "Help", new DialogInterface.OnClickListener()
    {
        public void onClick(DialogInterface dialog, int which)
        {
            Toast.makeText(getApplicationContext(), "You chose Help. EOLC", Toast.LENGTH_SHORT).show();
            wv.loadUrl("file:///android_asset/otherpages/errorpage.htm");
        }
    });

    alertDialog.setNegativeButton( "Exit", new DialogInterface.OnClickListener()
    {
        public void onClick(DialogInterface dialog, int which)
        {
            // Write your code here to execute after dialog
            Toast.makeText(getApplicationContext(), "You chose to exit.", Toast.LENGTH_SHORT).show();
            finish();
            }
    });

    alertDialog.create();
    alertDialog.show();
}


public void roe()
{
    AlertDialog.Builder alertDialog = new AlertDialog.Builder( MainActivity.this );

    alertDialog.setTitle("ERROR 2");
    alertDialog.setMessage("Host is unreachable. Restart to load cache or exit.");
    alertDialog.setIcon(R.drawable.tick);
    alertDialog.setPositiveButton( "Restart", new DialogInterface.OnClickListener()
    {
        public void onClick(DialogInterface dialog,int which)
        {
            Toast.makeText(getApplicationContext(), "You chose to restart and load cache.", Toast.LENGTH_SHORT).show();
            Intent i = getBaseContext().getPackageManager()
                     .getLaunchIntentForPackage( getBaseContext().getPackageName() );
            i.addFlags(Intent.FLAG_ACTIVITY_CLEAR_TOP | Intent.FLAG_ACTIVITY_NEW_TASK );
            startActivity(i);
        }
    });
    alertDialog.setNeutralButton( "Help", new DialogInterface.OnClickListener()
    {
        public void onClick(DialogInterface dialog, int which)
        {
            Toast.makeText(getApplicationContext(), "You chose Help. ROE", Toast.LENGTH_SHORT).show();
            wv.stopLoading();
            wv.loadUrl("file:///android_asset/otherpages/errorpage.htm");
        }
    });
    alertDialog.setNegativeButton( "Exit", new DialogInterface.OnClickListener()
    {
        public void onClick(DialogInterface dialog, int which)
        {
            Toast.makeText(getApplicationContext(), "You chose to exit.", Toast.LENGTH_SHORT).show();
            finish();
        }
    });
    alertDialog.create();
    alertDialog.show();
}


private class wvc extends WebViewClient
{

      //when page started loading
      public void onPageStarted(WebView view, String url, Bitmap favicon)
      {
          //circular progress bar open
          progress.setVisibility(View.VISIBLE);

          //if reachable and setting cache on every new page
          //setcache(getApplicationContext());

          WebSettings ws = wv.getSettings();

          if ( !reachable(getApplicationContext()) )
          {
              if ( ws.getCacheMode() == WebSettings.LOAD_DEFAULT )
              {
                  roe();
              }
              else if ( ws.getCacheMode() == WebSettings.LOAD_CACHE_ELSE_NETWORK )
              {
                  Toast.makeText(getApplicationContext(), "loading cache coz not reachable", Toast.LENGTH_SHORT).show();
              }

          }
      }


      //when page finished
      @Override
      public void onPageFinished(WebView view, String url) 
      {
          super.onPageFinished(view, mycaturl);
          Toast.makeText(getApplicationContext(), "PAGE DONE LOADING!!", Toast.LENGTH_SHORT).show();

          //circular progress bar close
          progress.setVisibility(View.GONE);
      }


      //when received an error
      @Override
      public void onReceivedError(WebView view, int errorCode, String description, String failingUrl)
      {
          wv.stopLoading();
          //wv.loadUrl("file:///android_asset/otherpages/errorpage.htm");
          WebSettings ws = wv.getSettings();

          if ( ws.getCacheMode() == WebSettings.LOAD_DEFAULT )
          {
              Toast.makeText(getApplicationContext(), "Page unavailable", Toast.LENGTH_SHORT).show();
          }
          else
          {
              Toast.makeText(getApplicationContext(), "Page not cached", Toast.LENGTH_SHORT).show();
          }
          roe();
      }
  }


//checking connectivity by checking if site is reachable
public static boolean reachable(Context context) 
{
    final ConnectivityManager connMgr = (ConnectivityManager) context.getSystemService(Context.CONNECTIVITY_SERVICE);
    final NetworkInfo netInfo = connMgr.getActiveNetworkInfo();

    if (netInfo != null && netInfo.isConnected()) 
    {
        try 
        {
            URL url = new URL(mycaturl);
            HttpURLConnection urlc = (HttpURLConnection) url.openConnection();
            urlc.setConnectTimeout(5000); // five seconds timeout in milliseconds
            urlc.connect();
            if (urlc.getResponseCode() == 200) // good response
            {   return true;    } else {    return false;   }
        }
        catch (IOException e)
        {   return false;   }
    }
    else
    {   return false;   }
}


//options menu inflation
@Override
public boolean onCreateOptionsMenu(Menu menu) 
{
    // inflate the menu; this adds items to the action bar if it is present.
    getMenuInflater().inflate(R.menu.main, menu);
    return true;
}


//when back button is pressed
public void onBackPressed ()
{
    if (wv.isFocused() && wv.canGoBack())
    {   wv.goBack();    }   else {  finish();   }
}


//when options button is pressed
@Override

public boolean onOptionsItemSelected(MenuItem item)
{
    switch (item.getItemId())
    {
        case R.id.item1:
            wv.loadUrl("file:///android_asset/otherpages/errorpage.htm");
            break;
        case R.id.item2:
            String currurl=wv.getUrl();
            wv.loadUrl(currurl);   
            break;
        case R.id.item3:
            Intent i = getBaseContext().getPackageManager()
             .getLaunchIntentForPackage( getBaseContext().getPackageName() );
            i.addFlags(Intent.FLAG_ACTIVITY_CLEAR_TOP);
            startActivity(i);
            break;
        case R.id.item4:
            finish();
            break;
        default:
            break;
    }
    return true;
} 


//saving instance state
@Override
protected void onSaveInstanceState(Bundle outState )
{
    super.onSaveInstanceState(outState);
    wv.saveState(outState);
}


//restoring instance state
@Override
protected void onRestoreInstanceState(Bundle savedInstanceState)
{
    super.onSaveInstanceState(savedInstanceState);
    wv.restoreState(savedInstanceState);
}

}

是的，我也添加了这些:

<uses-permission android:name="android.permission.INTERNET" />
<uses-permission android:name="android.permission.ACCESS_NETWORK_STATE" />
<uses-permission android:name="android.permission.ACCESS_WIFI_STATE" /> 

Answer 1

好的，这是真正做到这一点的方法。

1)永远不要改变严格模式。需要这样做意味着 99% 的时间你没有以正确的方式编写它。严格模式是有原因的——阻止用户认为应用程序崩溃了。实际上，如果您触发看门狗定时器(您可能正在这样做)，禁用它可能会使应用程序崩溃。

2)永远不要写 if(x) else if (!x) else。最后一个 else 是多余的，else if 导致你再次执行 x，而这样做几乎总是错误的。

3) 有一种更好的方法来为对话计时。为您的 WebView 编写自定义 WebViewClient，并将其设置为 setWebViewClient。覆盖 onPageFinished 以设置全局标志以了解加载的页面。在您的 onCreate 中，创建 webview，设置此客户端并设置计时器。当计时器关闭时，检查标志。如果标志仍然为假，则停止加载网页并弹出对话框。

编辑:补充

4) 我刚刚注意到在 onPageStarted 中再次调用 reachable？真的太过分了。

如果你这样做:

1)你的buildwv函数变成你的onCreate函数，添加代码来设置自定义客户端和启动定时器

2)在检查全局标志后，您的 eolc 函数成为计时器的主体

3) 你的 roe 函数应该真的消失了。

4) 你的 onPageStarted 功能可能消失了。它看起来不像是在做任何对我有用的事情，而计时器没有处理它来检查页面是否已加载。保留它只是为了进度条的工作。

5)reachable 消失了。