url 打开期间浏览器 activity 出现空异常
Null exception in browser activity during url open
我有一个只有浏览器视图的 activity。每次应用程序尝试打开 url 我都会收到此异常:
Caused by: java.lang.NullPointerException: Attempt to invoke virtual method 'void android.webkit.WebView.loadUrl(java.lang.String)' on a null object reference
指的是这一行:
mWebView.loadUrl("http://google.com");
评论此行后,activity从另一个视图打开正常。这是尝试加载网页的代码:
public class Browser extends AppCompatActivity {
WebView mWebView;
/**
* ATTENTION: This was auto-generated to implement the App Indexing API.
* See https://g.co/AppIndexing/AndroidStudio for more information.
*/
private GoogleApiClient client;
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(layout.activity_browser);
mWebView = (WebView) findViewById(R.id.webView);
mWebView.loadUrl("http://google.com");
// ATTENTION: This was auto-generated to implement the App Indexing API.
// See https://g.co/AppIndexing/AndroidStudio for more information.
client = new GoogleApiClient.Builder(this).addApi(AppIndex.API).build();
}
Logcat:
java.lang.RuntimeException: Unable to start activity ComponentInfo{karolklimek.mpkdisplay2/karolklimek.mpkdisplay2.Browser}: java.lang.NullPointerException: Attempt to invoke virtual method 'void android.webkit.WebView.loadUrl(java.lang.String)' on a null object reference
at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2298)
at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2360)
at android.app.ActivityThread.access0(ActivityThread.java:144)
at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1278)
at android.os.Handler.dispatchMessage(Handler.java:102)
at android.os.Looper.loop(Looper.java:135)
at android.app.ActivityThread.main(ActivityThread.java:5221)
at java.lang.reflect.Method.invoke(Native Method)
at java.lang.reflect.Method.invoke(Method.java:372)
at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:899)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:694)
Caused by: java.lang.NullPointerException: Attempt to invoke virtual method 'void android.webkit.WebView.loadUrl(java.lang.String)' on a null object reference
at karolklimek.mpkdisplay2.Browser.onCreate(Browser.java:38)
at android.app.Activity.performCreate(Activity.java:5933)
at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1105)
at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2251)
at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2360)
at android.app.ActivityThread.access0(ActivityThread.java:144)
at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1278)
at android.os.Handler.dispatchMessage(Handler.java:102)
at android.os.Looper.loop(Looper.java:135)
at android.app.ActivityThread.main(ActivityThread.java:5221)
at java.lang.reflect.Method.invoke(Native Method)
at java.lang.reflect.Method.invoke(Method.java:372)
at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:899)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:694)
以及content_browserXML文件的内容:
<?xml version="1.0" encoding="utf-8"?>
<RelativeLayout 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:paddingBottom="@dimen/activity_vertical_margin"
android:paddingLeft="@dimen/activity_horizontal_margin"
android:paddingRight="@dimen/activity_horizontal_margin"
android:paddingTop="@dimen/activity_vertical_margin"
app:layout_behavior="@string/appbar_scrolling_view_behavior"
tools:context="karolklimek.mpkdisplay2.Browser"
>
<WebView
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:id="@+id/webView"
android:layout_alignParentBottom="true"
android:layout_alignParentEnd="true"
android:layout_alignParentTop="true"
android:layout_alignParentStart="true" />
</RelativeLayout>
您在 setContentView()
中有误。您必须从 R.java
文件传递布局的整数值。因此你必须传递 R.layout.activity_browser
而不是 layout.activity_browser
.
应该是
setContentView(R.layout.activity_browser);
更新
在您的代码中,您将内容视图设置为 activity_browser
,但根据您的问题,我了解到您在 content_browser.xml
文件中有 webview,因此您得到了一个 NPE。
解决该错误的最简单方法是将 webview 移动到您的 activity_browser.xml
或将您的 setContentView 更改为加载 content_browser
而不是 activity_browser
.
从代码中我们可以看到布局没有加载,因为 mWebView 对象没有初始化,你最终得到了 NPE。
代码应该是
setContentView(R.layout.activity_browser);
反而
setContentView(layout.activity_browser);
我有一个只有浏览器视图的 activity。每次应用程序尝试打开 url 我都会收到此异常:
Caused by: java.lang.NullPointerException: Attempt to invoke virtual method 'void android.webkit.WebView.loadUrl(java.lang.String)' on a null object reference
指的是这一行:
mWebView.loadUrl("http://google.com");
评论此行后,activity从另一个视图打开正常。这是尝试加载网页的代码:
public class Browser extends AppCompatActivity {
WebView mWebView;
/**
* ATTENTION: This was auto-generated to implement the App Indexing API.
* See https://g.co/AppIndexing/AndroidStudio for more information.
*/
private GoogleApiClient client;
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(layout.activity_browser);
mWebView = (WebView) findViewById(R.id.webView);
mWebView.loadUrl("http://google.com");
// ATTENTION: This was auto-generated to implement the App Indexing API.
// See https://g.co/AppIndexing/AndroidStudio for more information.
client = new GoogleApiClient.Builder(this).addApi(AppIndex.API).build();
}
Logcat:
java.lang.RuntimeException: Unable to start activity ComponentInfo{karolklimek.mpkdisplay2/karolklimek.mpkdisplay2.Browser}: java.lang.NullPointerException: Attempt to invoke virtual method 'void android.webkit.WebView.loadUrl(java.lang.String)' on a null object reference
at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2298)
at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2360)
at android.app.ActivityThread.access0(ActivityThread.java:144)
at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1278)
at android.os.Handler.dispatchMessage(Handler.java:102)
at android.os.Looper.loop(Looper.java:135)
at android.app.ActivityThread.main(ActivityThread.java:5221)
at java.lang.reflect.Method.invoke(Native Method)
at java.lang.reflect.Method.invoke(Method.java:372)
at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:899)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:694)
Caused by: java.lang.NullPointerException: Attempt to invoke virtual method 'void android.webkit.WebView.loadUrl(java.lang.String)' on a null object reference
at karolklimek.mpkdisplay2.Browser.onCreate(Browser.java:38)
at android.app.Activity.performCreate(Activity.java:5933)
at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1105)
at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2251)
at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2360)
at android.app.ActivityThread.access0(ActivityThread.java:144)
at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1278)
at android.os.Handler.dispatchMessage(Handler.java:102)
at android.os.Looper.loop(Looper.java:135)
at android.app.ActivityThread.main(ActivityThread.java:5221)
at java.lang.reflect.Method.invoke(Native Method)
at java.lang.reflect.Method.invoke(Method.java:372)
at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:899)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:694)
以及content_browserXML文件的内容:
<?xml version="1.0" encoding="utf-8"?>
<RelativeLayout 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:paddingBottom="@dimen/activity_vertical_margin"
android:paddingLeft="@dimen/activity_horizontal_margin"
android:paddingRight="@dimen/activity_horizontal_margin"
android:paddingTop="@dimen/activity_vertical_margin"
app:layout_behavior="@string/appbar_scrolling_view_behavior"
tools:context="karolklimek.mpkdisplay2.Browser"
>
<WebView
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:id="@+id/webView"
android:layout_alignParentBottom="true"
android:layout_alignParentEnd="true"
android:layout_alignParentTop="true"
android:layout_alignParentStart="true" />
</RelativeLayout>
您在 setContentView()
中有误。您必须从 R.java
文件传递布局的整数值。因此你必须传递 R.layout.activity_browser
而不是 layout.activity_browser
.
应该是
setContentView(R.layout.activity_browser);
更新
在您的代码中,您将内容视图设置为 activity_browser
,但根据您的问题,我了解到您在 content_browser.xml
文件中有 webview,因此您得到了一个 NPE。
解决该错误的最简单方法是将 webview 移动到您的 activity_browser.xml
或将您的 setContentView 更改为加载 content_browser
而不是 activity_browser
.
从代码中我们可以看到布局没有加载,因为 mWebView 对象没有初始化,你最终得到了 NPE。
代码应该是 setContentView(R.layout.activity_browser); 反而 setContentView(layout.activity_browser);