android - webview loadurl 崩溃应用程序

Question

我想创建一个可以在应用程序中打开网站的应用程序。所以我想使用webview。但是，当我使用“loadurl”功能时，该应用程序在手机(Android 4.2.2)上崩溃了。你知道问题出在哪里吗？

错误日志:

02-03 22:50:11.762  24750-24750/com.example.app E/AndroidRuntime﹕ FATAL EXCEPTION: main
java.lang.RuntimeException: Unable to start activity ComponentInfo{com.example.app/com.example.app.MainActivity}: java.lang.NullPointerException
        at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2205)
        at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2255)
        at android.app.ActivityThread.access$600(ActivityThread.java:146)
        at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1240)
        at android.os.Handler.dispatchMessage(Handler.java:99)
        at android.os.Looper.loop(Looper.java:137)
        at android.app.ActivityThread.main(ActivityThread.java:5171)
        at java.lang.reflect.Method.invokeNative(Native Method)
        at java.lang.reflect.Method.invoke(Method.java:511)
        at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:797)
        at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:564)
        at dalvik.system.NativeStart.main(Native Method)
 Caused by: java.lang.NullPointerException
        at com.example.app.MainActivity.onCreate(MainActivity.java:24)
        at android.app.Activity.performCreate(Activity.java:5200)
        at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1080)
        at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2169)
        at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2255)
        at android.app.ActivityThread.access$600(ActivityThread.java:146)
        at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1240)
        at android.os.Handler.dispatchMessage(Handler.java:99)
        at android.os.Looper.loop(Looper.java:137)
        at android.app.ActivityThread.main(ActivityThread.java:5171)
        at java.lang.reflect.Method.invokeNative(Native Method)
        at java.lang.reflect.Method.invoke(Method.java:511)
        at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:797)
        at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:564)
        at dalvik.system.NativeStart.main(Native Method)

代码如下:

public class MainActivity extends ActionBarActivity {
private WebView mWebView;
@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_main);

    mWebView = (WebView) findViewById(R.id.webView);

    mWebView.loadUrl("http://beta.html5test.com/");
}


@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;
}

@Override
public boolean onOptionsItemSelected(MenuItem item) {
    // Handle action bar item clicks here. The action bar will
    // automatically handle clicks on the Home/Up button, so long
    // as you specify a parent activity in AndroidManifest.xml.
    int id = item.getItemId();
    if (id == R.id.action_settings) {
        return true;
    }
    return super.onOptionsItemSelected(item);
}

/**
 * A placeholder fragment containing a simple view.
 */
public static class PlaceholderFragment extends Fragment {

    public PlaceholderFragment() {
    }

    @Override
    public View onCreateView(LayoutInflater inflater, ViewGroup container,
            Bundle savedInstanceState) {
        View rootView = inflater.inflate(R.layout.fragment_main, container, false);
        return rootView;
    }
}

}

Answer 1

NullPointerException 推断您的 onCreate() 方法中的变量正在解析为 null。由于您的 onCreate() 方法非常简单，我敢打赌如果您调试应用程序 mWebView 将为 null。将您的 activity_main.xml 布局设置为:

<?xml version="1.0" encoding="utf-8"?>
<WebView  xmlns:android="http://schemas.android.com/apk/res/android"
    android:id="@+id/webView"
    android:layout_width="fill_parent"
    android:layout_height="fill_parent"
/>

它应该可以工作。