【发布时间】：2013-08-19 19:39:29
【问题描述】：
我在一个 android 应用程序中使用 webview，我试图让它在保存设置后第二次启动应用程序时自动启动。设置断点后，我能够确定应用程序在 WebActivity 中的“mWebView.setWebChromeClient(new WebChromeClient()”行上崩溃了。我在调试器中找不到错误源。
网络活动：
public class WebActivity extends Activity
{
WebView mWebView;
@Override
public void onCreate(Bundle savedInstanceState)
{
super.onCreate(savedInstanceState);
final Activity mActivity = this;
// Adds Progress bar Support
this.getWindow().requestFeature(Window.FEATURE_PROGRESS);
setContentView(R.layout.activity_web);
// Makes Progress bar Visible
getWindow().setFeatureInt( Window.FEATURE_PROGRESS, Window.PROGRESS_VISIBILITY_ON);
mWebView = (WebView) findViewById( R.id.webview );
mWebView.getSettings().setBuiltInZoomControls(true);
mWebView.getSettings().setJavaScriptEnabled(true);
mWebView.getSettings().setDomStorageEnabled(true);
mWebView.setWebViewClient(new WebViewClient());
mWebView.setWebChromeClient(new WebChromeClient()
{
public void onProgressChanged(WebView view, int progress)
{
//Make the bar disappear after URL is loaded, and changes string to Loading...
findViewById(R.id.webview).setVisibility(View.GONE);
mActivity.setTitle("Loading...");
mActivity.setProgress(progress * 100); //Make the bar disappear after URL is loaded
// Return the app name after finish loading
if(progress == 100)
{
mActivity.setTitle(R.string.webtitle);
findViewById(R.id.webview).setVisibility(View.VISIBLE);
}
}
});
Bundle b = getIntent().getExtras();
mWebView.loadUrl("http://" + (b.getString("iptextfield")) + "/index.html");
WebView wv = (WebView) findViewById(R.id.webview);
wv.setWebViewClient(new WebViewClient()
{
boolean toast_f = true;
@Override
public void onReceivedError(WebView view, int errorCode, String description, String failingUrl)
{
Context context = getApplicationContext();
CharSequence text = "Loading...(this may take up to 60 seconds)";
if (toast_f)
{
toast_f = false;
int duration = Toast.LENGTH_LONG;
Toast toast = Toast.makeText(context, text, duration);
toast.setGravity(Gravity.CENTER|Gravity.CENTER,0,0);
toast.show();
}
Bundle b = getIntent().getExtras();
mWebView.loadUrl("http://" + (b.getString("iptextfield")) + "/index.html");
}
});
}
}
主要活动：
public class MainActivity extends Activity
{
@Override
protected void onCreate(Bundle savedInstanceState)
{
super.onCreate(savedInstanceState);
Intent intent;
SharedPreferences sharedPref= getSharedPreferences("mypref", 0);
String GetStatus = sharedPref.getString("DataSaved", "");
if (GetStatus.equals("true"))
{
intent = new Intent(this, WebActivity.class);
}
else
{
intent = new Intent(this, SetupActivity.class);
}
startActivity(intent);
finish();
}
}
这是我在运行应用程序时遇到的 logcat 错误：
08-19 12:25:54.407: W/dalvikvm(15158): threadid=1: thread exiting with uncaught exception (group=0x4202d438)
08-19 12:25:54.407: E/AndroidRuntime(15158): FATAL EXCEPTION: main
08-19 12:25:54.407: E/AndroidRuntime(15158): java.lang.RuntimeException: Unable to start activity ComponentInfo{com.webpage.WebActivity}: java.lang.NullPointerException
08-19 12:25:54.407: E/AndroidRuntime(15158): at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2073)
08-19 12:25:54.407: E/AndroidRuntime(15158): at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2098)
08-19 12:25:54.407: E/AndroidRuntime(15158): at android.app.ActivityThread.access$600(ActivityThread.java:138)
08-19 12:25:54.407: E/AndroidRuntime(15158): at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1204)
08-19 12:25:54.407: E/AndroidRuntime(15158): at android.os.Handler.dispatchMessage(Handler.java:99)
08-19 12:25:54.407: E/AndroidRuntime(15158): at android.os.Looper.loop(Looper.java:137)
08-19 12:25:54.407: E/AndroidRuntime(15158): at android.app.ActivityThread.main(ActivityThread.java:4911)
08-19 12:25:54.407: E/AndroidRuntime(15158): at java.lang.reflect.Method.invokeNative(Native Method)
08-19 12:25:54.407: E/AndroidRuntime(15158): at java.lang.reflect.Method.invoke(Method.java:511)
08-19 12:25:54.407: E/AndroidRuntime(15158): at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:790)
08-19 12:25:54.407: E/AndroidRuntime(15158): at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:557)
08-19 12:25:54.407: E/AndroidRuntime(15158): at dalvik.system.NativeStart.main(Native Method)
08-19 12:25:54.407: E/AndroidRuntime(15158): Caused by: java.lang.NullPointerException
08-19 12:25:54.407: E/AndroidRuntime(15158): at com.webpage.WebActivity.onCreate(WebActivity.java:58)
08-19 12:25:54.407: E/AndroidRuntime(15158): at android.app.Activity.performCreate(Activity.java:5240)
08-19 12:25:54.407: E/AndroidRuntime(15158): at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1082)
08-19 12:25:54.407: E/AndroidRuntime(15158): at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2037)
08-19 12:25:54.407: E/AndroidRuntime(15158): ... 11 more
【问题讨论】：
-
异常其实是
NullPointerException。WebActivity.java的58行是什么？ -
@A--C 第 58 行是 mWebView.loadUrl("http://"(b.getString("iptextfield")) + "/index.html");我没有在 sharedpreferences 中保存 iptextfield 的信息，这可能是问题吗？
-
是的，这就是问题所在。如果您请求的值不存在，
getString将返回 null。非常规命名的GetStatus变量也存在为空的风险。 -
@323go 但是，
null字符串与其他两个字符串连接。Bundle b很可能是null。 -
好的，谢谢。我是开发 android 应用程序的新手，直到 A--C 指出第 58 行导致问题时，我才知道如何解释 logcat。我现在知道了。 @A--C 你能输入答案让我勾选吗？