android - 如何使用 Butterknife 解决 NullPointerException void com.google.android.gms.ads.AdView.loadAd(com.google.android.gms.ads.AdRequest)

Question

实际上，我正在尝试制作一个具有免费和付费风格的应用程序。当我使用简单的 findViewById 方法进行绑定(bind)时，它工作正常。但是当我尝试添加butterKnife时，我拼命坚持使用butterKnife。

我正在尝试通过 MainActivity.java 文件中的 butterknife 绑定(bind)来绑定(bind)内容(例如 AdMob 或 Button)。但它首先显示空指针异常错误，它在 AdMob 对象上显示空指针异常。我运行干净的项目，然后它显示在button.onClickListener Nullpointer 异常上。

请帮助我...

这是错误:显示 AdMob nullpointerException:

09-08 19:04:30.860 19466-19466/? E/AndroidRuntime: FATAL EXCEPTION: main
                                                   Process: com.santossingh.jokeapp.free, PID: 19466
                                                   java.lang.RuntimeException: Unable to start activity ComponentInfo{com.santossingh.jokeapp.free/com.santossingh.jokeapp.free.MainActivity}: java.lang.NullPointerException: Attempt to invoke virtual method 'void com.google.android.gms.ads.AdView.loadAd(com.google.android.gms.ads.AdRequest)' on a null object reference
                                                       at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2416)
                                                       at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2476)
                                                       at android.app.ActivityThread.-wrap11(ActivityThread.java)
                                                       at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1344)
                                                       at android.os.Handler.dispatchMessage(Handler.java:102)
                                                       at android.os.Looper.loop(Looper.java:148)
                                                       at android.app.ActivityThread.main(ActivityThread.java:5417)
                                                       at java.lang.reflect.Method.invoke(Native Method)
                                                       at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:726)
                                                       at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:616)
                                                    Caused by: java.lang.NullPointerException: Attempt to invoke virtual method 'void com.google.android.gms.ads.AdView.loadAd(com.google.android.gms.ads.AdRequest)' on a null object reference
                                                       at com.santossingh.jokeapp.free.MainActivity.onCreate(MainActivity.java:62)
                                                       at android.app.Activity.performCreate(Activity.java:6237)
                                                       at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1107)
                                                       at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2369)
                                                       at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2476) 
                                                       at android.app.ActivityThread.-wrap11(ActivityThread.java) 
                                                       at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1344) 
                                                       at android.os.Handler.dispatchMessage(Handler.java:102) 
                                                       at android.os.Looper.loop(Looper.java:148) 
                                                       at android.app.ActivityThread.main(ActivityThread.java:5417) 
                                                       at java.lang.reflect.Method.invoke(Native Method) 
                                                       at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:726) 
                                                       at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:616) 
09-08 19:04:35.652 837-2192/system_process E/Surface: getSlotFromBufferLocked: unknown buffer: 0xf2cf6c90
09-08 19:04:56.030 837-853/system_process E/BluetoothAdapter: Bluetooth binder is null
09-08 19:06:20.986 837-853/system_process E/BluetoothAdapter: Bluetooth binder is null
09-08 19:07:41.011 837-853/system_process E/BluetoothAdapter: Bluetooth binder is null
09-08 19:09:01.042 837-853/system_process E/BluetoothAdapter: Bluetooth binder is null
09-08 19:10:20.982 837-853/system_process E/BluetoothAdapter: Bluetooth binder is null
09-08 19:11:46.019 837-853/system_process E/BluetoothAdapter: Bluetooth binder is null
09-08 19:13:06.051 837-853/system_process E/BluetoothAdapter: Bluetooth binder is null
09-08 19:14:41.018 837-853/system_process E/BluetoothAdapter: Bluetooth binder is null
09-08 19:16:06.047 837-853/system_process E/BluetoothAdapter: Bluetooth binder is null

2-MainActivity.java

public class MainActivity extends AppCompatActivity implements AsyncResponse{

    @BindView(R.id.avi) AVLoadingIndicatorView avLoadingIndicatorView;
    @BindView(R.id.button_jokeTeller) Button button_JokeTeller;
    @BindView(R.id.instruction_TextView)
    TextView instruction;
    @BindView(R.id.container) RelativeLayout relativeLayout;
    @BindView(R.id.adView) AdView adView;
    @BindView(R.id.progressBar) LinearLayout linearLayout;

    private InterstitialAd mInterstitialAd;
    EndpointsAsyncTask endpointsAsyncTask;
    private static final String JOKE_TAG="joke";

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        ButterKnife.bind(this);

        endpointsAsyncTask = new EndpointsAsyncTask(this);

        AdRequest adRequestBanner = new AdRequest.Builder().build();
        adView.loadAd(adRequestBanner);

        mInterstitialAd = new InterstitialAd(this);
        mInterstitialAd.setAdUnitId(getString(R.string.interstitial_ad_unit_id));
        AdRequest adRequestInterstitial = new AdRequest.Builder().build();
        mInterstitialAd.loadAd(adRequestInterstitial);

        button_JokeTeller.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                showInterstitial();
            }
        });

        mInterstitialAd.setAdListener(new AdListener() {
            @Override
            public void onAdClosed() {
                showProgressbar(true);
                showJoke();
            }

            @Override
            public void onAdFailedToLoad(int errorCode) {
                Toast.makeText(getApplicationContext(), "Ad failed to load! error code: " + errorCode, Toast.LENGTH_SHORT).show();
            }

            @Override
            public void onAdLeftApplication() {
                showProgressbar(true);
                Toast.makeText(getApplicationContext(), "Ad left application!", Toast.LENGTH_SHORT).show();
            }

            @Override
            public void onAdOpened() {
                Toast.makeText(getApplicationContext(), "Ad is opened!", Toast.LENGTH_SHORT).show();
            }
        });
    }
    private void showInterstitial() {
        if (mInterstitialAd.isLoaded()) {
            mInterstitialAd.show();
        }
    }

    public void showJoke(){
        endpointsAsyncTask.execute(getString(R.string.keyword));
    }

    @Override
    public void processFinish(String result) {
        Intent intent = new Intent(this, JokeActivity
                .class)
                .putExtra(JOKE_TAG, result);
        showProgressbar(false);
        startActivity(intent);
    }

    public void showProgressbar(boolean a){
        if(a==true){
            relativeLayout.setVisibility(View.GONE);
            linearLayout.setVisibility(View.VISIBLE);
        }else{
            linearLayout.setVisibility(View.GONE);
            relativeLayout.setVisibility(View.VISIBLE);
        }
    }
}

3-activity_main.xml文件

<?xml version="1.0" encoding="utf-8"?>
<RelativeLayout
    android:id="@+id/activity_main"
    xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:tools="http://schemas.android.com/tools"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:background="#0e73a6"
    android:padding="10dp"
    tools:context="com.santossingh.jokeapp.free.MainActivity"
    xmlns:ads="http://schemas.android.com/apk/res-auto"
    xmlns:app="http://schemas.android.com/apk/res-auto">
    <LinearLayout
        android:id="@+id/progressBar"
        android:layout_width="match_parent"
        android:gravity="center"
        android:layout_height="match_parent">

    <com.wang.avi.AVLoadingIndicatorView
        android:id="@+id/avi"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        style="@style/AVLoadingIndicatorView"
        android:visibility="visible"
        app:indicatorName="BallPulseIndicator"
    />
</LinearLayout>
    <RelativeLayout android:layout_width="match_parent"
                    android:layout_height="match_parent"
                    android:id="@+id/container">
        <TextView
            android:layout_width="match_parent"
            android:layout_height="wrap_content"
            android:text="@string/instructions"
            android:textColor="#fff"
            android:id="@+id/instruction_TextView"
        />

        <Button android:layout_width="wrap_content"
                android:layout_height="wrap_content"
                android:id="@+id/button_jokeTeller"
                android:layout_below="@+id/instruction_TextView"
                android:text="@string/button_text"
        />

        <!-- view for AdMob Banner Ad -->
        <com.google.android.gms.ads.AdView
            android:id="@+id/adView"
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:layout_alignParentBottom="true"
            android:layout_centerHorizontal="true"
            ads:adSize="BANNER"
            ads:adUnitId="@string/banner_ad_unit_id"/>
    </RelativeLayout>

</RelativeLayout>

4- list 文件

<manifest xmlns:android="http://schemas.android.com/apk/res/android">

    <uses-permission android:name="android.permission.INTERNET"/>
    <uses-permission android:name="android.permission.ACCESS_NETWORK_STATE"/>

    <application>
        <activity android:name="com.santossingh.jokeapp.free.MainActivity"
        >
            <!-- This meta-data tag is required to use Google Play Services. -->
            <meta-data
                android:name="com.google.android.gms.version"
                android:value="@integer/google_play_services_version"/>

            <intent-filter>
                <action android:name="android.intent.action.MAIN"/>
                <category android:name="android.intent.category.LAUNCHER"/>
            </intent-filter>
        </activity>
    </application>

    <activity
        android:name="com.google.android.gms.ads.AdActivity"
        android:configChanges="keyboard|keyboardHidden|orientation|screenLayout|uiMode|screenSize|smallestScreenSize"
        android:theme="@android:style/Theme.Translucent"/>
</manifest>

Answer 1

确保仅在 setContentView 命令之后添加三行 adMob

否则 - 此命令将返回 null 值:

 mAdView = findViewById(R.id.adView);

正确命令序列的示例:

setContentView(R.layout.activity_item_list);  // <== make asure this comes **BEFORE** the Admob mAdView commands

mAdView = findViewById(R.id.adView);
AdRequest adRequest = new AdRequest.Builder().build();
mAdView.loadAd(adRequest);