Question

我通过此代码获取第三方应用程序列表。

    ApplicationInfo ai;
    final PackageManager pm = main.getPackageManager();

    List<ApplicationInfo> packages1 = null;
    int index = 0;

    List<ApplicationInfo> packages = pm.getInstalledApplications(PackageManager.GET_META_DATA);

    for (ApplicationInfo appInfo : packages)
    {
        if ((appInfo.flags & ApplicationInfo.FLAG_SYSTEM) != 0)
        {
            // IS A SYSTEM APP
        }

        else 
        {
            packages1.add(index, appInfo);
            index++;
        }
    }

但是当我评论这一行时，我得到了一个例外：

    packages1.add(index, appInfo);

然后代码正确执行，但由于此行而导致异常。这是我的logcat：

07-01 05:19:32.058: W/dalvikvm(5558): threadid=8: thread exiting with uncaught exception (group=0x4001d7d0)
07-01 05:19:32.065: E/AndroidRuntime(5558): FATAL EXCEPTION: AsyncTask #1
07-01 05:19:32.065: E/AndroidRuntime(5558): java.lang.RuntimeException: An error occured while executing doInBackground()
07-01 05:19:32.065: E/AndroidRuntime(5558):     at android.os.AsyncTask$3.done(AsyncTask.java:200)
07-01 05:19:32.065: E/AndroidRuntime(5558):     at java.util.concurrent.FutureTask$Sync.innerSetException(FutureTask.java:273)
07-01 05:19:32.065: E/AndroidRuntime(5558):     at java.util.concurrent.FutureTask.setException(FutureTask.java:124)
07-01 05:19:32.065: E/AndroidRuntime(5558):     at java.util.concurrent.FutureTask$Sync.innerRun(FutureTask.java:307)
07-01 05:19:32.065: E/AndroidRuntime(5558):     at java.util.concurrent.FutureTask.run(FutureTask.java:137)
07-01 05:19:32.065: E/AndroidRuntime(5558):     at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1068)
07-01 05:19:32.065: E/AndroidRuntime(5558):     at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:561)
07-01 05:19:32.065: E/AndroidRuntime(5558):     at java.lang.Thread.run(Thread.java:1096)
07-01 05:19:32.065: E/AndroidRuntime(5558): Caused by: java.lang.NullPointerException
07-01 05:19:32.065: E/AndroidRuntime(5558):     at com.example.first.Fetch_Software.doInBackground(Fetch_Software.java:46)
07-01 05:19:32.065: E/AndroidRuntime(5558):     at com.example.first.Fetch_Software.doInBackground(Fetch_Software.java:1)
07-01 05:19:32.065: E/AndroidRuntime(5558):     at android.os.AsyncTask$2.call(AsyncTask.java:185)
07-01 05:19:32.065: E/AndroidRuntime(5558):     at java.util.concurrent.FutureTask$Sync.innerRun(FutureTask.java:305)
07-01 05:19:32.065: E/AndroidRuntime(5558):     ... 4 more
07-01 05:19:36.894: E/WindowManager(5558): Activity com.example.first.MainActivity has leaked window com.android.internal.policy.impl.PhoneWindow$DecorView@47faa8f8 that was originally added here
07-01 05:19:36.894: E/WindowManager(5558): android.view.WindowLeaked: Activity com.example.first.MainActivity has leaked window com.android.internal.policy.impl.PhoneWindow$DecorView@47faa8f8 that was originally added here
07-01 05:19:36.894: E/WindowManager(5558):  at android.view.ViewRoot.<init>(ViewRoot.java:247)
07-01 05:19:36.894: E/WindowManager(5558):  at android.view.WindowManagerImpl.addView(WindowManagerImpl.java:171)
07-01 05:19:36.894: E/WindowManager(5558):  at android.view.WindowManagerImpl.addView(WindowManagerImpl.java:114)
07-01 05:19:36.894: E/WindowManager(5558):  at android.view.Window$LocalWindowManager.addView(Window.java:424)
07-01 05:19:36.894: E/WindowManager(5558):  at android.app.Dialog.show(Dialog.java:241)
07-01 05:19:36.894: E/WindowManager(5558):  at com.example.first.MainActivity.onClick(MainActivity.java:114)
07-01 05:19:36.894: E/WindowManager(5558):  at java.lang.reflect.Method.invokeNative(Native Method)
07-01 05:19:36.894: E/WindowManager(5558):  at java.lang.reflect.Method.invoke(Method.java:521)
07-01 05:19:36.894: E/WindowManager(5558):  at android.view.View$1.onClick(View.java:2067)
07-01 05:19:36.894: E/WindowManager(5558):  at android.view.View.performClick(View.java:2408)
07-01 05:19:36.894: E/WindowManager(5558):  at android.view.View$PerformClick.run(View.java:8818)
07-01 05:19:36.894: E/WindowManager(5558):  at android.os.Handler.handleCallback(Handler.java:587)
07-01 05:19:36.894: E/WindowManager(5558):  at android.os.Handler.dispatchMessage(Handler.java:92)
07-01 05:19:36.894: E/WindowManager(5558):  at android.os.Looper.loop(Looper.java:123)
07-01 05:19:36.894: E/WindowManager(5558):  at android.app.ActivityThread.main(ActivityThread.java:4627)
07-01 05:19:36.894: E/WindowManager(5558):  at java.lang.reflect.Method.invokeNative(Native Method)
07-01 05:19:36.894: E/WindowManager(5558):  at java.lang.reflect.Method.invoke(Method.java:521)
07-01 05:19:36.894: E/WindowManager(5558):  at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:871)
07-01 05:19:36.894: E/WindowManager(5558):  at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:629)
07-01 05:19:36.894: E/WindowManager(5558):  at dalvik.system.NativeStart.main(Native Method)

Answer 1

我想你错过了申报行。

应该是：

List<ApplicationInfo> packages1 = null;
packages1 = new ArrayList<ApplicationInfo>();

Answer 2

首先你这样做：

List<ApplicationInfo> packages1 = null;

然后你这样做：

packages1.add(index, appInfo);

转换为：

null.add(index, appInfo);

最终成为：

07-01 05:19:32.065: E/AndroidRuntime(5558): Caused by: java.lang.NullPointerException
07-01 05:19:32.065: E/AndroidRuntime(5558):     at com.example.first.Fetch_Software.doInBackground(Fetch_Software.java:46)

在您的日志中。

Answer 3

当您忘记初始化数据类型时发生空指针，这里您忘记初始化List。

只需按照以下方式初始化您的列表：

List<ApplicationInfo> packages1 = new List<ApplicationInfo>();

Answer 4

package1尚未初始化，请尝试以下操作：

package1 = new ArrayList<ApplicationInfo>();

如何在android（而不是ListView）中填充List

4 个答案: