java - android java 在第二个 init 的 view.setonclicklistener 处出现空指针异常为什么它们不匹配

Question

我遇到了这个问题，它显示了以下错误

请帮助我:我在 init2() 中收到 NullPointerException。显然短信为空。我不明白这个问题

Process: com.example.android.projectdestage, PID: 11049 java.lang.RuntimeException: Unable to start activity ComponentInfo{com.example.android.projectdestage/com.example.android.projectdestage.MainActivity}: java.lang.NullPointerException: Attempt to invoke virtual method 'void android.view.View.setOnClickListener(android.view.View$OnClickListener)' on a null object reference at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2984) at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:3045) at android.app.ActivityThread.-wrap14(ActivityThread.java) at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1642) at android.os.Handler.dispatchMessage(Handler.java:102) at android.os.Looper.loop(Looper.java:154) at android.app.ActivityThread.main(ActivityThread.java:6776) at java.lang.reflect.Method.invoke(Native Method) at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:1518) at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:1408) Caused by: java.lang.NullPointerException: Attempt to invoke virtual method 'void android.view.View.setOnClickListener(android.view.View$OnClickListener)' on a null object reference at com.example.android.projectdestage.MainActivity.init2(MainActivity.java:60) at com.example.android.projectdestage.MainActivity.onCreate(MainActivity.java:38) at android.app.Activity.performCreate(Activity.java:6956) at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1126) at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2927) at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:3045)  at android.app.ActivityThread.-wrap14(ActivityThread.java)  at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1642)  at android.os.Handler.dispatchMessage(Handler.java:102)  at android.os.Looper.loop(Looper.java:154)  at android.app.ActivityThread.main(ActivityThread.java:6776)  at java.lang.reflect.Method.invoke(Native Method)  at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:1518)  at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:1408)

****这是我的主要 Activity ****

    import android.app.Dialog;
    import android.content.Intent;
    import android.os.Bundle;
    import android.support.v7.app.AppCompatActivity;
    import android.util.Log;
    import android.view.View;
    import android.widget.Button;
    import android.widget.Toast;

    import com.google.android.gms.common.ConnectionResult;
    import com.google.android.gms.common.GoogleApiAvailability;

    public class MainActivity extends AppCompatActivity


    {

    private Button sms;
    private Button btnMap;


        private static final String TAG = "MainActivity";

        private static final int ERROR_DIALOG_REQUEST = 9001;


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



            if(isServicesOK()){
                init();
                init2();
            }
        }


        private void init(){
            Button btnMap = (Button) findViewById(R.id.btnMap);
            btnMap.setOnClickListener(new View.OnClickListener() {
                @Override
                public void onClick(View view) {
                    Intent intent = new Intent(MainActivity.this, MapActivity.class);
                    startActivity(intent);

                }
            });
        }

        private void init2()
        {
            Button sms = (Button) findViewById(R.id.sms);
            sms.setOnClickListener(new View.OnClickListener() {
                @Override
                public void onClick(View v) {
                    Intent message = new Intent(MainActivity.this, MainActivity2.class);
                    startActivity(message);
                }
            });
        }







        public boolean isServicesOK()
        {
            Log.d(TAG, "isServicesOK: checking google services version");

            int available = GoogleApiAvailability.getInstance().isGooglePlayServicesAvailable(MainActivity.this);

            if(available == ConnectionResult.SUCCESS)
            {
                // koulchi mli7 map request
                Log.d(TAG, "isServicesOK: Google Play Services is working");
                return true;
            }
            else if(GoogleApiAvailability.getInstance().isUserResolvableError(available))
            {
                //test d erreur
                Log.d(TAG, "isServicesOK: an error occured but we can fix it");
                Dialog dialog = GoogleApiAvailability.getInstance().getErrorDialog(MainActivity.this, available, ERROR_DIALOG_REQUEST);
                dialog.show();
            }else
                {
                Toast.makeText(this, "You can't make map requests", Toast.LENGTH_SHORT).show();
                }
            return false;
        }



    }

`**this is my mainactivity xml**`



        <?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="com.example.android.projectdestage.MainActivity">

        <Button
            android:id="@+id/btnMap"
            android:layout_width="87dp"
            android:layout_height="45dp"
            android:layout_marginEnd="8dp"
            android:layout_marginStart="8dp"
            android:layout_marginTop="244dp"
            android:text="@string/map"
            app:layout_constraintEnd_toEndOf="parent"
            app:layout_constraintHorizontal_bias="0.43"
            app:layout_constraintStart_toStartOf="parent"
            app:layout_constraintTop_toTopOf="parent" />

        <Button
            android:id="@+id/smsbtn"
            android:layout_width="wrap_content"
            android:layout_height="43dp"
            android:layout_marginBottom="136dp"
            android:layout_marginEnd="8dp"
            android:layout_marginStart="8dp"
            android:layout_marginTop="8dp"
            android:text="@string/enter_your_message"
            app:layout_constraintBottom_toBottomOf="parent"
            app:layout_constraintEnd_toEndOf="parent"
            app:layout_constraintHorizontal_bias="0.43"
            app:layout_constraintStart_toStartOf="parent" />

    </android.support.constraint.ConstraintLayout>

**and the main2activity xml**

    <?xml version="1.0" encoding="utf-8"?>
<LinearLayout 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"
    android:gravity="center"

    android:orientation="vertical"
    tools:context="com.example.android.projectdestage.MainActivity2">


    <TextView
        android:id="@+id/editText"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text="@string/enter_your_message"
        android:textSize="30sp" />

    <LinearLayout
        android:layout_width="match_parent"
        android:layout_height="519dp"
        android:orientation="vertical">

        <TextView
            android:id="@+id/editText2"
            android:layout_width="385dp"
            android:layout_height="410dp"
            android:layout_marginTop="50dp"
            android:layout_weight="1"
            android:text="@string/textview" />

        <Button
            android:id="@+id/btnSendSMSendSms"
            android:layout_width="wrap_content"
            android:layout_height="250dp"
            android:layout_marginLeft="150dp"
            android:layout_marginStart="150dp"
            android:layout_marginVertical="110dp"

            android:layout_weight="1"
            android:text="@string/sendsms"
            tools:targetApi="o" />

    </LinearLayout>

    </LinearLayout>

和mapactivity xml 我认为主要问题在这里

<?xml version="1.0" encoding="utf-8"?>
<RelativeLayout 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">

    <fragment 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:id="@+id/map"
        tools:context=".MapsActivity"
        android:name="com.google.android.gms.maps.SupportMapFragment" />

    <RelativeLayout
        android:layout_width="match_parent"
        android:layout_height="50dp"
        android:layout_marginTop="10dp"
        android:layout_marginRight="10dp"
        android:layout_marginLeft="10dp"
        android:elevation="10dp"
        android:background="@drawable/white_border"
        android:id="@+id/relLayout1" tools:targetApi="lollipop">

        <ImageView
            android:layout_width="15dp"
            android:layout_height="15dp"
            android:id="@+id/ic_magnify"
            android:layout_centerVertical="true"
            android:layout_marginLeft="10dp"
            android:src="@drawable/ic_magnify" android:contentDescription="@string/todoo" android:layout_marginStart="10dp" />

        <AutoCompleteTextView
            android:layout_width="match_parent"
            android:layout_height="match_parent"
            android:layout_toRightOf="@+id/ic_magnify"
            android:layout_centerVertical="true"
            android:textSize="15sp"
            android:textColor="#000"
            android:id="@+id/input_search"
            android:background="@null"
            android:hint="@string/enter_address_city_or_zip_code"
            android:imeOptions="actionSearch" android:layout_toEndOf="@+id/ic_magnify" />


    </RelativeLayout>

    <ImageView
        android:layout_width="40dp"
        android:layout_height="40dp"
        android:layout_below="@id/relLayout1"
        android:layout_alignParentRight="true"
        android:layout_marginRight="10dp"
        android:layout_marginTop="10dp"
        android:scaleType="centerCrop"
        android:id="@+id/ic_gps"
        android:src="@drawable/ic_gps" android:contentDescription="@string/todo" android:layout_alignParentEnd="true" android:layout_marginEnd="10dp" />

    <ImageView
        android:layout_width="40dp"
        android:layout_height="40dp"
        android:id="@+id/place_picker"
        android:layout_marginLeft="10dp"
        android:layout_marginTop="15dp"
        android:scaleType="centerCrop"
        android:layout_below="@+id/relLayout1"
        android:src="@drawable/ic_map" android:contentDescription="@string/todoml" android:layout_marginStart="10dp" />

    <ImageView
        android:layout_width="40dp"
        android:layout_height="40dp"
        android:layout_below="@+id/place_picker"
        android:layout_marginLeft="10dp"
        android:layout_marginTop="15dp"
        android:scaleType="centerCrop"
        android:id="@+id/place_info"
        android:src="@drawable/ic_info" android:layout_marginStart="10dp" android:contentDescription="@string/todoop" />




</RelativeLayout>

谢谢谢谢谢谢谢谢谢谢谢谢谢谢谢谢谢谢谢谢你

谢谢谢谢谢谢谢谢谢谢谢谢谢谢谢谢谢谢谢谢你

Answer 1

Button sms = (Button) findViewById(R.id.sms); 返回 null

这意味着他无法在您的 activity_main.xml 布局中找到 R.id.sms。

可能是拼写错误或复制粘贴错误？检查此文件中此按钮的 ID 是否确实是 sms。

此外，如果您有针对不同屏幕尺寸的多种布局等。请检查所有这些。