我正在开发一个带有内部 web 视图的应用程序，仅限于一个站点，我希望它有一个向后刷新停止等...
这是我的代码：
package com.csu.stan.asiusu;
import android.content.Intent;
import android.graphics.Bitmap;
import android.net.Uri;
import android.os.Bundle;
import android.support.v4.app.NavUtils;
import android.webkit.WebSettings;
import android.webkit.WebView;
import android.webkit.WebViewClient;
import com.actionbarsherlock.app.SherlockActivity;
import com.actionbarsherlock.view.Menu;
import com.actionbarsherlock.view.MenuInflater;
import com.actionbarsherlock.view.MenuItem;
public class Site extends SherlockActivity {
private WebView myWebView;
private MenuItem fwdmenu, bckmenu, refmenu;
private boolean refresh = false;
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_site);
//webview
myWebView = (WebView) findViewById(R.id.webview);
myWebView.setWebViewClient(new mywebclient());
myWebView.setBackgroundColor(0);
myWebView.setBackgroundResource(R.drawable.back);
myWebView.clearHistory();
myWebView.clearCache(true);
myWebView.loadUrl("http://www.csustan.edu/asi-usu/new_index.php");
//webview settings
WebSettings webSettings = myWebView.getSettings();
webSettings.setJavaScriptEnabled(true);
webSettings.setUseWideViewPort(true);
webSettings.setDefaultZoom(WebSettings.ZoomDensity.FAR);
webSettings.setBuiltInZoomControls(true);
// Show the Up button in the action bar.
getSupportActionBar().setDisplayHomeAsUpEnabled(true);
}
//code called to update all icons
public void updateicons() {
if(myWebView.canGoBack()) {
bckmenu.setIcon(R.drawable.ic_menu_back);
bckmenu.setEnabled(true);}
else {
bckmenu.setEnabled(false);
bckmenu.setIcon(R.drawable.ic_menu_back_d); }
if(myWebView.canGoForward()) {
fwdmenu.setIcon(R.drawable.ic_menu_forward);
fwdmenu.setEnabled(true);}
else {
fwdmenu.setEnabled(false);
fwdmenu.setIcon(R.drawable.ic_menu_forward_d);}
}
private class mywebclient extends WebViewClient {
// handles "mailto:" html and opens the action chooser
public boolean shouldOverrideUrlLoading(WebView view, String url) {
if (url.startsWith("mailto:")) {
Intent intent = new Intent(Intent.ACTION_SENDTO,
Uri.parse(url));
startActivity(intent);
return true;
}else if(url.startsWith("http:") || url.startsWith("https:")) {
myWebView.loadUrl(url);
return false;
}
return true;
}
//on page load
public void onPageStarted(WebView view, String url, Bitmap favicon) {
//change refresh to stop
refresh = false;
refmenu.setIcon(R.drawable.ic_menu_stop);
updateicons();
}
//on page finished
public void onPageFinished(WebView view, String url) {
//change stop to refresh
updateicons();
refmenu.setIcon(R.drawable.ic_menu_refresh);
refresh = true;
}
}
@Override
public void onBackPressed()
{
// choose what back button does
if(myWebView.canGoBack())
myWebView.goBack();
else {
super.onBackPressed();
}
}
@Override
public boolean onCreateOptionsMenu(Menu menu) {
MenuInflater inflater = getSupportMenuInflater();
inflater.inflate(R.menu.activity_browsermenu, menu);
fwdmenu = menu.findItem(R.id.fwd);
bckmenu = menu.findItem(R.id.bck);
refmenu = menu.findItem(R.id.ref);
inflater.inflate(R.menu.activity_open, menu);
updateicons();
return true;
}
@Override
public boolean onOptionsItemSelected(MenuItem item) {
switch (item.getItemId()) {
//refresh/stop button
case R.id.ref:
if(refresh == true)
myWebView.reload();
if(refresh == false)
myWebView.stopLoading();
return true;
//back button
case R.id.bck:
if(myWebView.canGoBack())
myWebView.goBack();
updateicons();
return true;
//forward button
case R.id.fwd:
if(myWebView.canGoForward())
myWebView.goForward();
updateicons();
return true;
//open in browser button
case R.id.open:
Intent intent = new Intent(Intent.ACTION_VIEW).setData(Uri.parse("http://www.csustan.edu/asi-usu/new_index.php"));
startActivity(intent);
return true;
//home button
case android.R.id.home:
// This ID represents the Home or Up button. In the case of this
// activity, the Up button is shown. Use NavUtils to allow users
// to navigate up one level in the application structure. For
// more details, see the Navigation pattern on Android Design:
//
// http://developer.android.com/design/patterns/navigation.html#up-vs-back
//
NavUtils.navigateUpFromSameTask(this);
return true;
}
return super.onOptionsItemSelected(item);
}
}
这在纵向上工作得很好，但由于某些奇怪的原因它在横向上崩溃，这是错误：
如果我删除 onpagestarted 中的所有代码，则工作正常，但这显然会破坏刷新/停止。
05-06 11:09:05.594: E/AndroidRuntime(21915): FATAL EXCEPTION: main
05-06 11:09:05.594: E/AndroidRuntime(21915): java.lang.NullPointerException
05-06 11:09:05.594: E/AndroidRuntime(21915): at com.csu.stan.asiusu.Site.updateicons(Site.java:53)
05-06 11:09:05.594: E/AndroidRuntime(21915): at com.csu.stan.asiusu.Site$mywebclient.onPageStarted(Site.java:85)
05-06 11:09:05.594: E/AndroidRuntime(21915): at android.webkit.CallbackProxy.handleMessage(CallbackProxy.java:314)
05-06 11:09:05.594: E/AndroidRuntime(21915): at android.os.Handler.dispatchMessage(Handler.java:99)
05-06 11:09:05.594: E/AndroidRuntime(21915): at android.os.Looper.loop(Looper.java:137)
05-06 11:09:05.594: E/AndroidRuntime(21915): at android.app.ActivityThread.main(ActivityThread.java:5226)
05-06 11:09:05.594: E/AndroidRuntime(21915): at java.lang.reflect.Method.invokeNative(Native Method)
05-06 11:09:05.594: E/AndroidRuntime(21915): at java.lang.reflect.Method.invoke(Method.java:511)
05-06 11:09:05.594: E/AndroidRuntime(21915): at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:795)
05-06 11:09:05.594: E/AndroidRuntime(21915): at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:562)
05-06 11:09:05.594: E/AndroidRuntime(21915): at dalvik.system.NativeStart.main(Native Method)
任何帮助将不胜感激谢谢。