Question

我有一个应用程序，我在其中创建了一个获取AdvertId的单例类。但我无法通过Application上下文。我该怎么做，请检查我的代码并指导我？

Singleton类代码： -

private static AdIdFetcher ourInstance = null;
public static Context context;
private static String TAG = AdIdFetcher.class.getSimpleName();

interface AdIdFetcherResult {
    void onId(String advertId);
}

public AdIdFetcher(Context context) {
    this.context = context;
}

public static AdIdFetcher getOurInstance() {
    if (ourInstance == null) {
        ourInstance = new AdIdFetcher(context);
    }
    return ourInstance;
}

public void fetchId(final AdIdFetcherResult rcb) {
    AsyncTask<Void, Void, String> task = new AsyncTask<Void, Void, String>() {
        @Override
        protected String doInBackground(Void... params) {
            AdvertisingIdClient.Info id_Info = null;
            try {
                id_Info = AdvertisingIdClient.getAdvertisingIdInfo(context);
            } catch (IOException | GooglePlayServicesNotAvailableException | GooglePlayServicesRepairableException e) {
                e.printStackTrace();
            }
            String advertId = null;
            try {
                assert id_Info != null;
                advertId = id_Info.getId();
                Log.e(TAG, "Advertisement Id::::" + advertId);

            } catch (NullPointerException e) {
                e.printStackTrace();
            }
            rcb.onId(advertId);
            return advertId;
        }
    };
    task.execute();
}

调用类代码： -

 AdIdFetcher.getOurInstance().fetchId(new AdIdFetcher.AdIdFetcherResult() {
        @Override
        public void onId(String advertId) {
            Log.e(TAG,"Advert ID:::"+advertId);
        }
    });

logcat的

Caused by: java.lang.NullPointerException: null reference

Answer 1

您需要在调用getOurInstance()

时传递Context

public static AdIdFetcher getOurInstance(Context context) {
    if (ourInstance==null){
        ourInstance=new AdIdFetcher(context);
    }
    return ourInstance;
}

并将其称为

AdIdFetcher.getOurInstance(context).fetchId(new AdIdFetcher.AdIdFetcherResult() {
        @Override
        public void onId(String advertId) {
            Log.e(TAG,"Advert ID:::"+advertId);
        }
});

Answer 2

将上下文保持为静态字段会导致内存泄漏并且很糟糕，您不应该这样做，而是在fetchId方法本身中传递上下文。

public void fetchId(Context context, final AdIdFetcherResult rcb)

Answer 3

我认为你的调用代码是在Activity或任何Fragment中吗？

如果是碎片：

传递上下文＆＃34; getOurInstance（）＆＃34;像这样：
```
AdIdFetcher.getOurInstance(getActivity()).fetchId(.....
......
```
如果是活动：

传递上下文＆＃34; getOurInstance（）＆＃34;像这样：
```
AdIdFetcher.getOurInstance(classname.this).fetchId(.....
......
```

并在单件类中传递如下：

public static AdIdFetcher getOurInstance(Context context) {
  if (ourInstance==null){
    ourInstance=new AdIdFetcher(context);
  }
  return ourInstance;
}

并且您的代码存在问题，您在构造函数中获取上下文但从未在调用活动中调用该构造函数。

无法在单例类中传递应用程序上下文？

3 个答案: