实例变量越来越设置为空，如果活动是由OS重建 [英] Instance variable getting set to null if activity is recreated by OS

问题描述

我一直在努力奋斗着这个问题相当长的一段时间了。

I have been struggling with this problem for quite some time now.

实例我的主要活动变量越来越设置，如果我一整天后启动的应用程序为null。所以，我的用户隔日应用程序崩溃一次，然后重新启动就好了。我假设的活动就会被杀死，并重新创建，当他们启动应用程序的第二天。

Instance variables of my main activity are getting set to null if I start app after a day. So, for my users every other day app crashes once and then restarts just fine. I am assuming that the activity gets killed and recreated and when they start app the next day.

基本上，可能会发生是由于onsavedinstance的意见得到重建，但这些观点需要的数据尚未公布，因为我不存储数据包。

Basically, what may be happening is due to "onsavedinstance" the views are getting recreated, but the data that those views need is not yet available as I do not store the data in the bundle.

如何prevent呢？我不倾向于存储每个变量包，因为它是一个不好的设计。什么是做到这一点的最好方法是什么？

How can I prevent it? I am not inclined towards storing each and every variable in bundle as it's a bad design. What's the best way to do it?

下面是我的code：

基本上我试图从服务器上填充的onCreate我的引导数据（dataWrapper）。我用在以后的code这个数据对象。一切工作正常，在第一次应用程序启动。但是，当用户经过一天或7-8小时打开的应用程序，对象dataWrapper原来是空。

Basically i am trying to populate my bootstrap data (dataWrapper) from server on "onCreate". I use this data object in subsequent code. All works fine on first app launch. But when user opens app after a day or 7-8 hours, the object "dataWrapper" turns out to be null.

    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        //other initialization code
        getData();
        //remaining code
    }

    protected DataWrapper dataWrapper;

    private void getData(){
    try {
        //url for fetching data 
        String url = "http://....."
        new FetchAndPopulateMarketDataAsyncTask(this){
            @Override public void onPostExecute(DataWrapper result)
            {
                if(result==null){
                    //server or no internet error 
                }
                else{
                    dataWrapper = (DataWrapper)result;
                }
            }
        }.execute(new URL(url));
    } catch (MalformedURLException e) {
        // TODO Auto-generated catch block
        e.printStackTrace();
    }
}

谢谢， 罗尼

Thanks, Rony

推荐答案

Android将杀死或根据需要释放的后台应用程序的内存。所以，你需要保持你的应用程序的状态，当它进入后台。

Android will kill or release memory of background applications as needed. So, you need to maintain state of your application when it goes into the background.

尝试重写双方的onSaveInstanceState和onRestoreInstanceState保存和恢复这些实例变量的值。

Try overriding both onSaveInstanceState and onRestoreInstanceState to save and restore the values of these instance variables.

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