Question

我想在Android.But中获取Android应用程序安装日期，当我运行应用程序获取NullPointerException时。有人帮助我。

这是我的代码

public void onCreate(Bundle savedInstanceState)
     {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.registration_details);

        try 
        {        long installed = 
                 context.getPackageManager().getPackageInfo("package.com.sqlitedemo",          
                 PackageManager.GET_META_DATA).firstInstallTime;
                 Log.e("installed  = ","  "  + installed);
        }
        catch (NameNotFoundException e) 
        {
            // TODO Auto-generated catch block
            e.printStackTrace();
        }
}

这是我的Log Cat错误

08-06 11:40:34.758: E/AndroidRuntime(335): FATAL EXCEPTION: main
08-06 11:40:34.758: E/AndroidRuntime(335): java.lang.RuntimeException: Unable to start activity ComponentInfo{com.sqlitedemo/com.sqlitedemo.Registration_Form}: java.lang.NullPointerException
08-06 11:40:34.758: E/AndroidRuntime(335):  at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:1647)
08-06 11:40:34.758: E/AndroidRuntime(335):  at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:1663)
08-06 11:40:34.758: E/AndroidRuntime(335):  at android.app.ActivityThread.access$1500(ActivityThread.java:117)
08-06 11:40:34.758: E/AndroidRuntime(335):  at android.app.ActivityThread$H.handleMessage(ActivityThread.java:931)
08-06 11:40:34.758: E/AndroidRuntime(335):  at android.os.Handler.dispatchMessage(Handler.java:99)
08-06 11:40:34.758: E/AndroidRuntime(335):  at android.os.Looper.loop(Looper.java:123)
08-06 11:40:34.758: E/AndroidRuntime(335):  at android.app.ActivityThread.main(ActivityThread.java:3683)
08-06 11:40:34.758: E/AndroidRuntime(335):  at java.lang.reflect.Method.invokeNative(Native Method)
08-06 11:40:34.758: E/AndroidRuntime(335):  at java.lang.reflect.Method.invoke(Method.java:507)
08-06 11:40:34.758: E/AndroidRuntime(335):  at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:839)
08-06 11:40:34.758: E/AndroidRuntime(335):  at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:597)
08-06 11:40:34.758: E/AndroidRuntime(335):  at dalvik.system.NativeStart.main(Native Method)
08-06 11:40:34.758: E/AndroidRuntime(335): Caused by: java.lang.NullPointerException
08-06 11:40:34.758: E/AndroidRuntime(335):  at com.sqlitedemo.Registration_Form.onCreate(Registration_Form.java:61)
08-06 11:40:34.758: E/AndroidRuntime(335):  at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1047)
08-06 11:40:34.758: E/AndroidRuntime(335):  at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:1611)
08-06 11:40:34.758: E/AndroidRuntime(335):  ... 11 more

感谢您的光临。

Answer 1

您确定需要吗

context.getPackageManager().getPackageInfo("package.com.sqlitedemo"

而不是

context.getPackageManager().getPackageInfo("com.sqlitedemo"

Answer 2

您可以在启动或主要活动中使用日历实例，并将其保存在共享首选项中，如下所示 -

    SharedPreference shared=getSharedPreferences(Preference.KEY_PREF,MODE_PRIVATE);
    Editor  edit=shared.edit();
        if(shared.getBoolean(Preference.KEY_FIRST_TIME, false)==false){
            edit.putBoolean(Preference.KEY_FIRST_TIME,true );
            Calendar first=Calendar.getInstance();
            edit.putLong(Preference.KEY_FIRST_DATE, first.getTimeInMillis());

这将在您的应用首次运行时存储日期，时间等

Answer 3

您尚未初始化context，因此返回null。

将您的代码更改为：

setContentView(R.layout.registration_details);
context = this;
try 
{        
    long installed = context.getPackageManager().getPackageInfo("package.com.sqlitedemo",          
                 PackageManager.GET_META_DATA).firstInstallTime;
    Log.e("installed  = ","  "  + installed);
}

因此，您的上下文将不再返回null。

Answer 4

我认为你的上下文是空的..

Context context;
public void onCreate(Bundle savedInstanceState)
 {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.registration_details);
    context=getBaseContext();
    try 
    {        long installed = 
             context.getPackageManager().getPackageInfo("package.com.sqlitedemo",          
             PackageManager.GET_META_DATA).firstInstallTime;
             Log.e("installed  = ","  "  + installed);
    }
    catch (NameNotFoundException e) 
    {
        // TODO Auto-generated catch block
        e.printStackTrace();
    }
 }

可能有帮助

此致

如何在Android中获取App安装日期的当前日期和时间

4 个答案: