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" />
最佳答案
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。
关于除非在浏览器中打开，否则 Android webview 不会加载，我们在Stack Overflow上找到一个类似的问题： https://stackoverflow.com/questions/18202269/