Question

我正在尝试从上下文菜单中启动用户选择中的另一个活动。代码上下文菜单的代码是：

case R.id.organize:
                   Log.d(LOGTAG, "Creating intent");
            Intent editIntent = new Intent(getApplicationContext(), AddToList.class);
            editIntent.putParcelableArrayListExtra("userPackageList", userPackages);
            Log.d(LOGTAG, "Starting activity");
            startActivity(editIntent);
            return true;

我的AndroidManifest.xml也有两个活动的条目：

<?xml version="1.0" encoding="utf-8"?>
<manifest xmlns:android="http://schemas.android.com/apk/res/android"
      package="com.firstapp.MyPackage"
      android:versionCode="1"
      android:versionName="1.0">


    <application android:icon="@drawable/icon" android:label="@string/app_name">
        <activity android:name=".ActivityOne"
                  android:label="@string/app_name">
            <intent-filter>
                <action android:name="android.intent.action.MAIN" />
                <category android:name="android.intent.category.LAUNCHER" />
            </intent-filter>
        </activity>

        <activity android:name=".ActivityTwo"
                  android:label="@string/app_name">
        </activity>
    </application>
</manifest>

输出在switch case中打印两个日志语句，然后崩溃，但出现以下异常：

07-18 12:32:29.516: ERROR/AndroidRuntime(601): FATAL EXCEPTION: main
07-18 12:32:29.516: ERROR/AndroidRuntime(601): java.lang.RuntimeException: Unable to instantiate activity ComponentInfo{com.firstapp.MyPackage/com.firstapp.MyPackage.ActivityTwo}: java.lang.NullPointerException
07-18 12:32:29.516: ERROR/AndroidRuntime(601):     at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2585)
07-18 12:32:29.516: ERROR/AndroidRuntime(601):     at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2679)
07-18 12:32:29.516: ERROR/AndroidRuntime(601):     at android.app.ActivityThread.access$2300(ActivityThread.java:125)
07-18 12:32:29.516: ERROR/AndroidRuntime(601):     at android.app.ActivityThread$H.handleMessage(ActivityThread.java:2033)
07-18 12:32:29.516: ERROR/AndroidRuntime(601):     at android.os.Handler.dispatchMessage(Handler.java:99)
07-18 12:32:29.516: ERROR/AndroidRuntime(601):     at android.os.Looper.loop(Looper.java:123)
07-18 12:32:29.516: ERROR/AndroidRuntime(601):     at android.app.ActivityThread.main(ActivityThread.java:4627)
07-18 12:32:29.516: ERROR/AndroidRuntime(601):     at java.lang.reflect.Method.invokeNative(Native Method)
07-18 12:32:29.516: ERROR/AndroidRuntime(601):     at java.lang.reflect.Method.invoke(Method.java:521)
07-18 12:32:29.516: ERROR/AndroidRuntime(601):     at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:868)
07-18 12:32:29.516: ERROR/AndroidRuntime(601):     at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:626)
07-18 12:32:29.516: ERROR/AndroidRuntime(601):     at dalvik.system.NativeStart.main(Native Method)
07-18 12:32:29.516: ERROR/AndroidRuntime(601): Caused by: java.lang.NullPointerException
07-18 12:32:29.516: ERROR/AndroidRuntime(601):     at android.app.Activity.setContentView(Activity.java:1647)
07-18 12:32:29.516: ERROR/AndroidRuntime(601):     at android.app.ListActivity.ensureList(ListActivity.java:314)
07-18 12:32:29.516: ERROR/AndroidRuntime(601):     at android.app.ListActivity.getListView(ListActivity.java:299)
07-18 12:32:29.516: ERROR/AndroidRuntime(601):     at com.firstapp.MyPackage.ActivityTwo.<init>(ActivityTwo.java:23)
07-18 12:32:29.516: ERROR/AndroidRuntime(601):     at java.lang.Class.newInstanceImpl(Native Method)
07-18 12:32:29.516: ERROR/AndroidRuntime(601):     at java.lang.Class.newInstance(Class.java:1429)
07-18 12:32:29.516: ERROR/AndroidRuntime(601):     at android.app.Instrumentation.newActivity(Instrumentation.java:1021)
07-18 12:32:29.516: ERROR/AndroidRuntime(601):     at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2577)

ActivityTwo的oncreate（）方法如下：

@Override
public void onCreate(Bundle savedInstanceState) 
{
    super.onCreate(savedInstanceState);
    ArrayList<PackageInfo> installedPkg = new ArrayList<PackageInfo>();
    installedPkg = getIntent().getParcelableArrayListExtra ("userPackageList"); 
    addItemsToList(installedPkg);
    setContentView(R.layout.main);
}

Answer 1

修改

根据您的说明，您的ActivityTwo看起来像这样：

public class ActivityTwo extends ListActivity { public ListView listView = getListView(); @Override public void onCreate(Bundle savedInstanceState) { super.onCreate(savedInstanceState); ArrayList<PackageInfo> installedPkg = new ArrayList<PackageInfo>(); installedPkg = getIntent().getParcelableArrayListExtra ("userPackageList"); addItemsToList(installedPkg); setContentView(R.layout.main); } //Other functions follow }

我认为异常是由public ListView listView = getListView();行引起的。也许您可以尝试将代码重写为以下内容：

public class ActivityTwo extends ListActivity { public ListView listView; @Override public void onCreate(Bundle savedInstanceState) { super.onCreate(savedInstanceState); setContentView(R.layout.main); listView = getListView(); } @Override public void onResume() { ArrayList<PackageInfo> installedPkg = new ArrayList<PackageInfo>(); installedPkg = getIntent().getParcelableArrayListExtra ("userPackageList"); addItemsToList(installedPkg); } //Other functions follow }

<强> ORIGIN：

也许我是愚蠢的，但在您的代码示例中，您将编辑意图定义为：

Intent editIntent = new Intent(getApplicationContext(), AddToList.class);

但我在manifest.xml中没有看到任何AddToList活动定义（您有ActivityOne和ActivityTwo）

还有一种情况需要注意getApplicationContext()。 Using Application context everywhere?

Answer 2

你好在你的清单文件中添加你的活动名称正确地标记了通信的名称。

这里假设您的活动名称是AddToList.java

活动android：name =“。AddToList” 机器人：标签= “@串/ APP_NAME”

但是在你的menfest ur活动名称你写的：ActivityTwo 所以在清单文件中尝试标记

Answer 3

只需使用即可查看R.id值。您使用的所有值必须出现在setContentview

中设置的布局中

从另一个活动开始一个活动时，空指针异常

3 个答案: