java - 网页 View 崩溃

Question

我正在使用 WebView 编写一个 Webbrowser，到目前为止一切正常。我不知道我做了什么导致每次打开应用程序时崩溃。 Android Studio 没有给我任何代码错误，所以我找不到问题所在。这是我的代码:

主 Activity .java

package riveras.kasparsweblser;

import android.os.Bundle;
import android.support.v7.app.AppCompatActivity;
import android.support.v7.widget.Toolbar;
import android.view.KeyEvent;

import android.webkit.WebChromeClient;
import android.webkit.WebView;
import android.webkit.WebViewClient;

public class MainActivity extends AppCompatActivity {

WebView webview;

private WebView mWebView;

@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_main);
    Toolbar toolbar = (Toolbar) findViewById(R.id.toolbar);
    setSupportActionBar(toolbar);
    String url = "http://www.google.com";
    webview = (WebView) findViewById(R.id.webView);
    webview.getSettings().setJavaScriptEnabled(true);
    webview.loadUrl(url);
    webview.setWebChromeClient(new WebChromeClient());
    webview.setWebViewClient(new WebViewClient());

}

@Override
public boolean onKeyDown(int keyCode, KeyEvent event) {
    mWebView = (WebView) findViewById(R.id.webView);
    if (event.getAction() == KeyEvent.ACTION_DOWN) {
        switch (keyCode) {
            case KeyEvent.KEYCODE_BACK:
                if (mWebView.canGoBack()) {
                    mWebView.goBack();
                } else {
                    finish();
                }
                return true;
        }

    }
    return super.onKeyDown(keyCode, event);
 }
}

activity_main.xml

<?xml version="1.0" encoding="utf-8"?>
<android.support.design.widget.CoordinatorLayout
xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:app="http://schemas.android.com/apk/res-auto"
xmlns:tools="http://schemas.android.com/tools" android:layout_width="match_parent"
android:layout_height="match_parent" android:fitsSystemWindows="true"
tools:context=".MainActivity">

<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:tools="http://schemas.android.com/tools"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    tools:context=".MainActivity" >

    <WebView
        android:layout_width="fill_parent"
        android:layout_height="fill_parent"
        android:id="@+id/wv"
        android:layout_below="@+id/toolbar"
        android:layout_alignParentBottom="true" />

    <android.support.v7.widget.Toolbar android:id="@+id/toolbar"
        android:layout_width="match_parent" android:layout_height="?attr/actionBarSize"
        android:background="?attr/colorPrimary" app:popupTheme="@style/AppTheme.PopupOverlay"
        android:clickable="true"
        android:contextClickable="true"
        android:elevation="1dp"
        android:focusable="false"
        android:max="@integer/status_bar_notification_info_maxnum"
        android:indeterminate="false"
        android:layout_alignParentTop="true"
        android:layout_alignParentStart="true"
        android:layout_alignParentEnd="true" />

</RelativeLayout>

</android.support.design.widget.CoordinatorLayout>

content_main.xml

<?xml version="1.0" encoding="utf-8"?>
<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:tools="http://schemas.android.com/tools"
xmlns:app="http://schemas.android.com/apk/res-auto"     android:layout_width="match_parent"

app:layout_behavior="@string/appbar_scrolling_view_behavior"
tools:showIn="@layout/activity_main" tools:context=".MainActivity"
android:layout_height="match_parent">

<WebView
    android:layout_width="wrap_content"
    android:layout_height="wrap_content"
    android:id="@+id/webView"
    android:layout_alignParentTop="true"
    android:layout_alignParentStart="true"
    android:layout_alignParentEnd="true"
    android:layout_alignParentBottom="true" />

 </RelativeLayout>

AndroidManifest.xml

<?xml version="1.0" encoding="utf-8"?>
<manifest xmlns:android="http://schemas.android.com/apk/res/android"
package="riveras.kasparsweblser" >

<uses-permission android:name="android.permission.INTERNET"/>

<application
    android:allowBackup="true"
    android:icon="@mipmap/ic_launcher"
    android:label="@string/app_name"
    android:supportsRtl="true"
    android:theme="@style/AppTheme" >
    <activity
        android:name=".MainActivity"
        android:label="@string/app_name"
        android:theme="@style/AppTheme.NoActionBar" >
        <intent-filter>
            <action android:name="android.intent.action.MAIN" />

            <category android:name="android.intent.category.LAUNCHER" />
        </intent-filter>
    </activity>
</application>

</manifest>

我得到的错误是:

11-23 18:46:56.045 32505-32505/? E/AndroidRuntime: FATAL EXCEPTION: main
       Process: riveras.kasparsweblser, PID: 32505
       java.lang.RuntimeException: Unable to start activity ComponentInfo{riveras.kasparsweblser/riveras.kasparsweblser.MainActivity}: java.lang.NullPointerException: Attempt to invoke virtual method 'android.webkit.WebSettings android.webkit.WebView.getSettings()' on a null object reference
           at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2356)
           at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2418)
           at android.app.ActivityThread.access$900(ActivityThread.java:154)
           at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1321)
           at android.os.Handler.dispatchMessage(Handler.java:102)
           at android.os.Looper.loop(Looper.java:135)
           at android.app.ActivityThread.main(ActivityThread.java:5291)
           at java.lang.reflect.Method.invoke(Native Method)
           at java.lang.reflect.Method.invoke(Method.java:372)
           at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:904)
           at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:699)
        Caused by: java.lang.NullPointerException: Attempt to invoke virtual method 'android.webkit.WebSettings android.webkit.WebView.getSettings()' on a null object reference
           at riveras.kasparsweblser.MainActivity.onCreate(MainActivity.java:26)
           at android.app.Activity.performCreate(Activity.java:5990)
           at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1106)
           at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2309)
           at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2418) 
           at android.app.ActivityThread.access$900(ActivityThread.java:154) 
           at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1321) 
           at android.os.Handler.dispatchMessage(Handler.java:102) 
           at android.os.Looper.loop(Looper.java:135) 
           at android.app.ActivityThread.main(ActivityThread.java:5291) 
           at java.lang.reflect.Method.invoke(Native Method) 
           at java.lang.reflect.Method.invoke(Method.java:372) 
           at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:904) 
           at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:699) 

感谢所有帮助，如果您需要更多代码来查看错误，请告诉我。

谢谢

/里维拉

Answer 1

您正在调用 setContentView(R.layout.activity_main);，它会加载一个布局文件，其中包含一个 WebView 和 android:id="@+ id/wv。您正在尝试调用 findViewById(R.id.webView);。您的小部件 ID 不匹配，它们需要匹配。