我最近开始学习Android开发,想要使用WebView来显示网页。我从Google网站上提供的示例中学到了一些东西,但出现了一个问题:模拟器一直提示页面不可用。我在StackOverflow上搜索并找到了与WebViewClient相关的链接。我尝试了那个方法,但还是没有成功,我已经多次检查了Manifest文件中是否有网络权限的条目。作为测试,我运行了模拟器中可用的浏览器,我的防火墙弹出了一个问题,询问是否允许其访问。但当我从程序中运行时,弹窗却没有出现。我所拥有的代码就是在Google页面上给出的。
mWebView = (WebView) findViewById(R.id.webview);
mWebView.getSettings().setJavaScriptEnabled(true);
mWebView.loadUrl("http://www.google.com");
mWebView.setWebViewClient(new HelloWebViewClient());
private class HelloWebViewClient extends WebViewClient {
@Override
public boolean shouldOverrideUrlLoading(WebView view, String url) {
view.loadUrl(url);
return true;
}
我尝试使用loadData直接加载简单的HTML,它可以正常工作。我不知道发生了什么以及如何解决这个问题。如果有任何帮助,我将不胜感激。
在此添加Android清单。
<?xml version="1.0" encoding="utf-8"?>
<manifest xmlns:android="http://schemas.android.com/apk/res/android"
package="com.example.hellowebview"
android:versionCode="1"
android:versionName="1.0">
<uses-sdk android:minSdkVersion="8" />
<application android:icon="@drawable/icon" android:label="@string/app_name">
<activity android:name=".HelloWebView"
android:label="@string/app_name"
android:theme="@android:style/Theme.NoTitleBar">
<intent-filter>
<action android:name="android.intent.action.MAIN" />
<category android:name="android.intent.category.LAUNCHER" />
</intent-filter>
</activity>
<uses-permission android:name="android.permission.INTERNET" />
</application>
</manifest>
为了检查是否仅为WebView的问题,我尝试使用httpGet和httpResonse类访问互联网,并遇到了同样的问题,代码无法连接到给定的站点。它失败并声明如下:
05-10 00:37:53.191: WARN/System.err(294): java.net.UnknownHostException: feeds.feedburner.com
05-10 00:37:53.230: WARN/System.err(294): at java.net.InetAddress.lookupHostByName(InetAddress.java:513)
05-10 00:37:53.230: WARN/System.err(294): at java.net.InetAddress.getAllByNameImpl(InetAddress.java:278)
05-10 00:37:53.230: WARN/System.err(294): at java.net.InetAddress.getAllByName(InetAddress.java:242)
05-10 00:37:53.250: WARN/System.err(294): at org.apache.http.impl.conn.DefaultClientConnectionOperator.openConnection(DefaultClientConnectionOperator.java:136)
05-10 00:37:53.250: WARN/System.err(294): at org.apache.http.impl.conn.AbstractPoolEntry.open(AbstractPoolEntry.java:164)
05-10 00:37:53.250: WARN/System.err(294): at org.apache.http.impl.conn.AbstractPooledConnAdapter.open(AbstractPooledConnAdapter.java:119)
05-10 00:37:53.271: WARN/System.err(294): at org.apache.http.impl.client.DefaultRequestDirector.execute(DefaultRequestDirector.java:348)
05-10 00:37:53.271: WARN/System.err(294): at org.apache.http.impl.client.AbstractHttpClient.execute(AbstractHttpClient.java:555)
05-10 00:37:53.280: WARN/System.err(294): at org.apache.http.impl.client.AbstractHttpClient.execute(AbstractHttpClient.java:487)
05-10 00:37:53.291: WARN/System.err(294): at org.apache.http.impl.client.AbstractHttpClient.execute(AbstractHttpClient.java:465)
05-10 00:37:53.301: WARN/System.err(294): at com.example.hellowebview.HelloWebView.onCreate(HelloWebView.java:43)
05-10 00:37:53.301: WARN/System.err(294): at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1047)
05-10 00:37:53.309: WARN/System.err(294): at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2627)
05-10 00:37:53.322: WARN/System.err(294): at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2679)
05-10 00:37:53.330: WARN/System.err(294): at android.app.ActivityThread.access$2300(ActivityThread.java:125)
05-10 00:37:53.340: WARN/System.err(294): at android.app.ActivityThread$H.handleMessage(ActivityThread.java:2033)
05-10 00:37:53.350: WARN/System.err(294): at android.os.Handler.dispatchMessage(Handler.java:99)
05-10 00:37:53.350: WARN/System.err(294): at android.os.Looper.loop(Looper.java:123)
05-10 00:37:53.361: WARN/System.err(294): at android.app.ActivityThread.main(ActivityThread.java:4627)
05-10 00:37:53.361: WARN/System.err(294): at java.lang.reflect.Method.invokeNative(Native Method)
05-10 00:37:53.372: WARN/System.err(294): at java.lang.reflect.Method.invoke(Method.java:521)
05-10 00:37:53.380: WARN/System.err(294): at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:868)
05-10 00:37:53.380: WARN/System.err(294): at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:626)
05-10 00:37:53.401: WARN/System.err(294): at dalvik.system.NativeStart.main(Native Method)
05-10 00:37:56.773: WARN/ActivityManager(58): Launch timeout has expired, giving up wake lock!
05-10 00:37:58.083: WARN/ActivityManager(58): Activity idle timeout for HistoryRecord{44fc9108 com.example.hellowebview/.HelloWebView}
05-10 00:38:06.300: DEBUG/KeyguardViewMediator(58): pokeWakelock(5000)
05-10 00:38:06.651: INFO/ARMAssembler(58): generated scanline__00000077:03545404_00000004_00000000 [ 47 ipp] (67 ins) at [0x3724c8:0x3725d4] in 7266287 ns
05-10 00:38:06.720: INFO/ARMAssembler(58): generated scanline__00000177:03515104_00001001_00000000 [ 91 ipp] (114 ins) at [0x371380:0x371548] in 1486222 ns
05-10 00:38:30.430: DEBUG/AndroidRuntime(294): Shutting down VM
05-10 00:38:30.430: WARN/dalvikvm(294): threadid=1: thread exiting with uncaught exception (group=0x4001d800)
05-10 00:38:30.752: ERROR/AndroidRuntime(294): FATAL EXCEPTION: main
05-10 00:38:30.752: ERROR/AndroidRuntime(294): java.lang.RuntimeException: Unable to start activity ComponentInfo{com.example.hellowebview/com.example.hellowebview.HelloWebView}: java.lang.NullPointerException
05-10 00:38:30.752: ERROR/AndroidRuntime(294): at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2663)
05-10 00:38:30.752: ERROR/AndroidRuntime(294): at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2679)
05-10 00:38:30.752: ERROR/AndroidRuntime(294): at android.app.ActivityThread.access$2300(ActivityThread.java:125)
05-10 00:38:30.752: ERROR/AndroidRuntime(294): at android.app.ActivityThread$H.handleMessage(ActivityThread.java:2033)
05-10 00:38:30.752: ERROR/AndroidRuntime(294): at android.os.Handler.dispatchMessage(Handler.java:99)
05-10 00:38:30.752: ERROR/AndroidRuntime(294): at android.os.Looper.loop(Looper.java:123)
05-10 00:38:30.752: ERROR/AndroidRuntime(294): at android.app.ActivityThread.main(ActivityThread.java:4627)
05-10 00:38:30.752: ERROR/AndroidRuntime(294): at java.lang.reflect.Method.invokeNative(Native Method)
05-10 00:38:30.752: ERROR/AndroidRuntime(294): at java.lang.reflect.Method.invoke(Method.java:521)
05-10 00:38:30.752: ERROR/AndroidRuntime(294): at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:868)
05-10 00:38:30.752: ERROR/AndroidRuntime(294): at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:626)
05-10 00:38:30.752: ERROR/AndroidRuntime(294): at dalvik.system.NativeStart.main(Native Method)
05-10 00:38:30.752: ERROR/AndroidRuntime(294): Caused by: java.lang.NullPointerException
05-10 00:38:30.752: ERROR/AndroidRuntime(294): at com.example.hellowebview.HelloWebView.onCreate(HelloWebView.java:51)
05-10 00:38:30.752: ERROR/AndroidRuntime(294): at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1047)
05-10 00:38:30.752: ERROR/AndroidRuntime(294): at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2627)
05-10 00:38:30.752: ERROR/AndroidRuntime(294): ... 11 more
知道了。由于权限设置的顺序很重要,我更改了清单文件中的权限设置顺序,然后它就起作用了。以下是已修改的清单文件:
<?xml version="1.0" encoding="utf-8"?>
<manifest xmlns:android="http://schemas.android.com/apk/res/android"
package="com.example.hellowebview"
android:versionCode="1"
android:versionName="1.0">
<uses-sdk android:minSdkVersion="8" />
<uses-permission android:name="android.permission.INTERNET" />
<application android:icon="@drawable/icon" android:label="@string/app_name">
<activity android:name=".HelloWebView"
android:label="@string/app_name"
android:theme="@android:style/Theme.NoTitleBar">
<intent-filter>
<action android:name="android.intent.action.MAIN" />
<category android:name="android.intent.category.LAUNCHER" />
</intent-filter>
</activity>
</application>
</manifest>
我不确定这个的意义是什么,但如果有人能详细解释一下就好了。