java - 是否可以从其他类访问主 Activity 中的插页式广告？

Question

我想在单击按钮时显示插页式广告，但我为插页式广告构建了一个单独的类，并在该类中创建了一个方法。现在我希望在启动屏幕上，当我在启动屏幕中输入单击按钮时，它会访问 Interstitial 类的方法并显示广告，但是当我单击按钮时，它会在 Interstitial 类中给出错误。

启动画面

package com.deitel.adsmobapp;

import androidx.appcompat.app.AppCompatActivity;

import android.content.Intent;
import android.os.Bundle;
import android.view.View;
import android.widget.Button;
import com.google.android.gms.ads.AdRequest;
import com.google.android.gms.ads.AdView;
import com.google.android.gms.ads.InterstitialAd;
import com.google.android.gms.ads.MobileAds;
import com.google.android.gms.ads.NativeExpressAdView;

public class SplashScreen extends AppCompatActivity {
    private AdView mAdview;
    Button btn_move;
    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_splash_screen);
        btn_move=findViewById(R.id.btn_move);
        btn_move.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                Interstitial interstitial=new Interstitial();
                interstitial.prepareAd();
                Intent i=new Intent(SplashScreen.this,MainActivity.class);
                startActivity(i);
            }
        });
        /*Banner Ads*/
        MobileAds.initialize(this,"ca-app-pub-3940256099942544~3347511713");
        mAdview=findViewById(R.id.adView);
        AdRequest adRequest=new AdRequest.Builder().build();
        mAdview.loadAd(adRequest);

    }

    @Override
    protected void onPause() {
        super.onPause();
        finish();
    }
}

插页式类

package com.deitel.adsmobapp;

import android.app.Activity;
import android.app.Application;
import android.util.Log;
import com.google.android.gms.ads.AdRequest;
import com.google.android.gms.ads.InterstitialAd;

public class Interstitial extends Application {
    private InterstitialAd interstitialAd;

    @Override
    public void onCreate() {
        super.onCreate();

        SplashScreen splashScreen=new SplashScreen();
        interstitialAd = new InterstitialAd(splashScreen);
        interstitialAd.setAdUnitId("ca-app-pub-3940256099942544/1033173712");
        AdRequest adRequest=new AdRequest.Builder().build();
        interstitialAd.loadAd(adRequest);
        prepareAd();
    }
    public void prepareAd() {

        if (interstitialAd.isLoaded())
        {
            interstitialAd.show();
        }
        else
            {
                Log.d("tag","Ads is not loaded");
            }

    }
}

错误

01-06 17:05:51.907 7044-7044/com.deitel.adsmobapp E/AndroidRuntime: FATAL EXCEPTION: main
    java.lang.NullPointerException
        at com.deitel.adsmobapp.Interstitial.prepareAd(Interstitial.java:26)
        at com.deitel.adsmobapp.SplashScreen$1.onClick(SplashScreen.java:31)
        at android.view.View.performClick(View.java:4084)
        at android.view.View$PerformClick.run(View.java:16966)

        at android.os.Handler.dispatchMessage(Handler.java:92)

Answer 1

该错误是 Interstiatil 类的方法 prepareAd() 第 26 行中的 NPE。interstitialAd 为 null，因为它是在创建 Activity 时调用的 onCreate() 中初始化的。您应该将您的类更改为从 Activity 而不是 Application 继承。并且不要在 onClick 方法中调用prepareAd()。

public class Interstitial extends Activity

在prepareAd()方法中检查null可能是明智之举:

public void prepareAd() {
    if (interstitialAd != null && interstitialAd.isLoaded())
    {
        interstitialAd.show();
    }
    else
        {
            Log.d("tag","Ads is not loaded");
        }
}