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我创建了一个应用程序，用户单击获取硬币按钮，在 Texview 中添加了 10 个硬币。用户有单独的登录界面。但是当我集成 Firebase 实时保存数据时，它会崩溃。

我希望每当用户单击 getCoins 按钮时，应在文本字段中添加硬币，并且这些硬币也应反映在我的 Firebase 数据中。

Activity_Main 布局。 

    <?xml version="1.0" encoding="utf-8"?>
<android.support.constraint.ConstraintLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:app="http://schemas.android.com/apk/res-auto"
    xmlns:tools="http://schemas.android.com/tools"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    tools:context=".MainActivity">

    <android.support.v7.widget.Toolbar
        android:id="@+id/main_toolbar_id"
        android:layout_width="match_parent"
        android:background="@color/colorPrimary"
        android:layout_height="wrap_content">
    </android.support.v7.widget.Toolbar>

    <RelativeLayout
        android:layout_width="match_parent"
        android:layout_height="match_parent"
        android:orientation="vertical">

        <Button
            android:id="@+id/btn"
            android:layout_width="200dp"
            android:layout_height="66dp"
            android:layout_gravity="center"
            android:gravity="center"
            android:text="GET COINS"
            android:textSize="20sp"
            android:textStyle="bold"
            android:layout_centerVertical="true"
            android:layout_centerHorizontal="true"
            />

        <TextView
            android:id="@+id/edittext"
            android:layout_width="317dp"
            android:layout_height="50dp"
            android:layout_alignParentTop="true"
            android:layout_centerHorizontal="true"
            android:layout_gravity="center"
            android:layout_marginTop="124dp"
            android:gravity="center"
            android:text="COINS: 0"
            android:textSize="40sp"
            android:textStyle="bold" />


    </RelativeLayout>

</android.support.constraint.ConstraintLayout>

Main Activity Class



public class MainActivity extends AppCompatActivity {
    int CoinAmount = 0;
    private Toolbar mainToolbar;
    private  FirebaseAuth mAuth;
    String myStringData;
    Firebase myFirebase;
    TextView myEditText;
    Button btngetcoin;

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

        myStringData = myEditText.getText().toString();
        Firebase.setAndroidContext(this);

        myFirebase = new Firebase("https://xpensive-b5178.firebaseio.com");
        btngetcoin.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                Firebase myNewChild= myFirebase.child("PresentCoin");

            }
        });
        btngetcoin= (Button)findViewById(R.id.btn);
        myEditText = (TextView)findViewById(R.id.edittext);

        final RewardedVideoAd RewardAd = MobileAds.getRewardedVideoAdInstance(this);
        RewardAd.loadAd("ca-app-pub-3940256099942544/5224354917", new AdRequest.Builder().build());
        MobileAds.initialize(this);

        btngetcoin.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                if(RewardAd.isLoaded()){
                    RewardAd.show();
                }else{
                    RewardAd.loadAd("ca-app-pub-3940256099942544/5224354917", new AdRequest.Builder().build());

                }
            }
        });
        RewardAd.setRewardedVideoAdListener(new RewardedVideoAdListener() {
            @Override
            public void onRewardedVideoAdLoaded() {

            }

            @Override
            public void onRewardedVideoAdOpened() {

            }

            @Override
            public void onRewardedVideoStarted() {

            }

            @Override
            public void onRewardedVideoAdClosed() {

            }

            @Override
            public void onRewarded(RewardItem rewardItem) {
                CoinAmount= CoinAmount +10;
                myEditText.setText("COINS: "+ CoinAmount);

            }

            @Override
            public void onRewardedVideoAdLeftApplication() {

            }

            @Override
            public void onRewardedVideoAdFailedToLoad(int i) {


            }

            @Override
            public void onRewardedVideoCompleted() {

            }
        });

Logcat 错误-

06-30 20:20:24.988 6074-6074/com.vikramgehlot.xpensive E/AndroidRuntime: FATAL EXCEPTION: main

   Process: com.vikramgehlot.xpensive, PID: 6074

   java.lang.RuntimeException: Unable to start activity ComponentInfo{com.vikramgehlot.xpensive/com.vikramgehlot.xpensive.MainActivity}: java.lang.NullPointerException: Attempt to invoke virtual method 'void android.widget.Button.setOnClickListener(android.view.View$OnClickListener)' on a null object reference

       at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2687)

       at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2753)

       at android.app.ActivityThread.access$1100(ActivityThread.java:186)

       at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1609)

       at android.os.Handler.dispatchMessage(Handler.java:111)

       at android.os.Looper.loop(Looper.java:238)

       at android.app.ActivityThread.main(ActivityThread.java:6016)

       at java.lang.reflect.Method.invoke(Native Method)

       at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:937)

       at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:798)

    Caused by: java.lang.NullPointerException: Attempt to invoke virtual method 'void android.widget.Button.setOnClickListener(android.view.View$OnClickListener)' on a null object reference

       at com.vikramgehlot.xpensive.MainActivity.onCreate(MainActivity.java:45)

       at android.app.Activity.performCreate(Activity.java:6466)

       at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1113)

       at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2640)

       at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2753) 

       at android.app.ActivityThread.access$1100(ActivityThread.java:186) 

       at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1609) 

       at android.os.Handler.dispatchMessage(Handler.java:111) 

       at android.os.Looper.loop(Looper.java:238) 

       at android.app.ActivityThread.main(ActivityThread.java:6016) 

       at java.lang.reflect.Method.invoke(Native Method) 

       at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:937) 

       at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:798) 
4

2 回答 2

0

变量 btngetcoin 未使用对您拥有的按钮对象的引用进行初始化。将以下 findViewById() 代码移到您设置的 setOnClickListener 上方，

    myFirebase = new Firebase("https://xpensive-b5178.firebaseio.com");
    // you need to initialize this before attaching listener!!
    btngetcoin= (Button)findViewById(R.id.btn);

    btngetcoin.setOnClickListener(new View.OnClickListener() {
        @Override
        public void onClick(View v) {
            Firebase myNewChild= myFirebase.child("PresentCoin");

        }
    });
于 2018-07-01T02:47:23.363 回答
0

如果您想将数据保存在 firebase 实时数据库中，那么您只需要执行以下操作

 mDatabase = FirebaseDatabase.getInstance().getReference().child("Users").child(mAuth.getCurrentUser().getUid());

参考您的数据库，然后像这样保存它

mDatabase.child("Key").setValue(value);

或者您可以从此链接https://firebase.google.com/docs/database/android/read-and-write获取参考

于 2018-06-30T10:52:30.397 回答