java - Admob 间质性单例模式 java.lang.NullPointerException :

Question

我正在使用Singleton模式来显示Admob Interstitial。其实模拟器上没问题。我在不同的智能手机上尝试过，没有问题。一切都运转良好。但当涉及到 Google Play 开发者控制台时，我遇到了这些错误。

java.lang.RuntimeException: 
  at android.app.ActivityThread.performLaunchActivity (ActivityThread.java:2200)
  at android.app.ActivityThread.handleLaunchActivity (ActivityThread.java:2250)
  at android.app.ActivityThread.access$800 (ActivityThread.java:139)
  at android.app.ActivityThread$H.handleMessage (ActivityThread.java:1200)
  at android.os.Handler.dispatchMessage (Handler.java:102)
  at android.os.Looper.loop (Looper.java:136)
  at android.app.ActivityThread.main (ActivityThread.java:5105)
  at java.lang.reflect.Method.invokeNative (Native Method)
  at java.lang.reflect.Method.invoke (Method.java:515)
  at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run (ZygoteInit.java:792)
  at com.android.internal.os.ZygoteInit.main (ZygoteInit.java:608)
  at dalvik.system.NativeStart.main (Native Method)
Caused by: java.lang.NullPointerException: 
  at x.y.z.ViewItemActivity.onCreate (ViewItemActivity.java:48)
  at android.app.Activity.performCreate (Activity.java:5275)
  at android.app.Instrumentation.callActivityOnCreate (Instrumentation.java:1087)
  at android.app.ActivityThread.performLaunchActivity (ActivityThread.java:2164)

由:java.lang.NullPointerException引起: 在 x.y.z.ViewItemActivity.onCreate (ViewItemActivity.java:48)

ViewItemActivity 中的第 48 行:

if (ad.isLoaded()) {//Line 48
            ad.show();
        }

让我展示一下 AdManager 类和用法

AdManager 类:

package x;

import android.app.Activity;
import android.content.Context;
import android.content.res.Resources;
import android.util.Log;

import com.google.android.gms.ads.AdRequest;
import com.google.android.gms.ads.InterstitialAd;

import x.y.z.R;
import x.y.z.app.App;

public class AdManager {


    static InterstitialAd ad;
    private Context ctx;

    public AdManager(Context ctx) {
        this.ctx = ctx;
    }

    public void createAd() {
        // Create an ad.
        ad = new InterstitialAd(ctx);
        ad.setAdUnitId(App.getResourses().getString(R.string.interstitial_ad_unit));

        final AdRequest adRequest = new AdRequest.Builder().build();

        // Load the interstitial ad.
        ad.loadAd(adRequest);

       // Log.d("admobshowing","asdf");
    }

    public InterstitialAd getAd() {
        return ad;
    }
}

我在OnCreate中的MainActivity中请求:

AdManager adManager = new AdManager(MainActivity.this);
adManager.createAd();

我在另一个 Activity - ViewItemActivity - setContentView 之前显示它:

@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    AdManager adManager = new AdManager(ViewItemActivity.this);
    InterstitialAd ad = adManager.getAd();
    if (ad.isLoaded()) {
        ad.show();
    }

    setContentView(R.layout.activity_view_item);

....

....

当用户按后退按钮时再次请求:- ViewItemActivity

@Override
public void onBackPressed(){
AdManager adManager = new AdManager(ViewItemActivity.this);
adManager.createAd();
super.onBackPressed();
}

因此，当我单独尝试时，我在模拟器或真实智能手机中不会出现错误，但在 Google Play 开发者控制台中，我会遇到数十个空指针异常。我该如何解决我的问题？

Answer 1

我认为单例模式不适合您的用例。您正在尝试为每个上下文创建一个新广告，因此在 AdManager 实例中保留该广告没有任何好处。您可以将 AdManager 更改为以下内容，并删除对 createAd 的所有调用。

public class AdManager {

    private InterstitialAd ad;
    private Context ctx;

    public AdManager(Context ctx) {
        this.ctx = ctx;
    }

    private void createAd() {
        // Create an ad.
        ad = new InterstitialAd(ctx);
        ad.setAdUnitId(App.getResourses().getString(R.string.interstitial_ad_unit));

        final AdRequest adRequest = new AdRequest.Builder().build();

        // Load the interstitial ad.
        ad.loadAd(adRequest);
    }

    public InterstitialAd getAd() {
        if (ad == null) {
            createAd();
        }
        return ad;
    }
}