Question

我在调试模式下运行应用程序然后继续崩溃。在logicat监视器上，它说：

Caused by: java.lang.NullPointerException: Attempt to invoke virtual method 'void android.widget.ImageButton.setOnClickListener(android.view.View$OnClickListener)' on a null object reference
at nws.iceapp.MainActivity.imgButtonLoadPage(MainActivity.java:174)
at nws.iceapp.MainActivity.onCreate(MainActivity.java:160)

这是我点击（MainActivity.java:174）

时弹出的内容

protected void imgButtonLoadPage (int buttonID, final int activity) {
    ImageButton imgBtn = (ImageButton) findViewById(buttonID);

        imgBtn.setOnClickListener(new OnClickListener() {
            @Override
            public void onClick(View v) {
                setContentView(activity);
            }
        });

特别是从imgButtonLoadpage开始，当我点击（MainActivity.java:160）时，弹出：

            imgButtonLoadPage(R.id.asthma, R.layout.act_ast);
            imgButtonLoadPage(R.id.vomiting, R.layout.act_vom);
            imgButtonLoadPage(R.id.unconscious, R.layout.act_unc);
            imgButtonLoadPage(R.id.fracture2, R.layout.act_fra);
            imgButtonLoadPage(R.id.dislocate2, R.layout.act_dis);
            imgButtonLoadPage(R.id.heart_attack2, R.layout.act_hea);

        }

这是布局xml代码：

<?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="nws.iceapp.MainActivity">

    <ScrollView
        android:id="@+id/scrollView2"
        android:layout_width="368dp"
        android:layout_height="518dp"
        android:layout_marginBottom="8dp"
        android:layout_marginLeft="8dp"
        android:layout_marginRight="8dp"
        android:layout_marginTop="8dp"
        app:layout_constraintBottom_toBottomOf="parent"
        app:layout_constraintHorizontal_bias="0.506"
        app:layout_constraintLeft_toLeftOf="parent"
        app:layout_constraintRight_toRightOf="parent"
        app:layout_constraintTop_toTopOf="parent">

        <LinearLayout
            android:layout_width="match_parent"
            android:layout_height="wrap_content"
            android:orientation="vertical"
            android:weightSum="1">

            <ImageButton

                android:id="@+id/asthma"
                android:layout_width="match_parent"
                android:layout_height="115dp"
                android:layout_marginBottom="8dp"
                android:layout_marginEnd="8dp"
                android:layout_marginLeft="8dp"
                android:layout_marginRight="8dp"
                android:layout_marginStart="8dp"
                android:layout_marginTop="8dp"
                android:layout_weight="1.16"
                android:scaleType="centerCrop"
                android:src="@drawable/asthma_icon"
                app:layout_constraintBottom_toBottomOf="parent"
                app:layout_constraintHorizontal_bias="0.189"
                app:layout_constraintLeft_toLeftOf="parent"
                app:layout_constraintRight_toRightOf="parent"
                app:layout_constraintTop_toTopOf="parent"
                app:layout_constraintVertical_bias="0.11" />

            <TextView
                android:id="@+id/ast"
                android:layout_width="match_parent"
                android:layout_height="wrap_content"
                android:gravity="center"
                android:text="Asthma"
                android:background="#333"
                android:textColor="#fff"
                android:textSize="21sp" />


            <ImageButton
                android:id="@+id/vomiting"
                android:layout_width="match_parent"
                android:layout_height="115dp"
                android:layout_marginBottom="8dp"
                android:layout_marginEnd="8dp"
                android:layout_marginLeft="8dp"
                android:layout_marginRight="8dp"
                android:layout_marginStart="8dp"
                android:layout_marginTop="8dp"
                android:layout_weight="0.47"
                android:scaleType="centerCrop"
                android:src="@drawable/vomit_icon"
                app:layout_constraintBottom_toBottomOf="parent"
                app:layout_constraintHorizontal_bias="0.189"
                app:layout_constraintLeft_toLeftOf="parent"
                app:layout_constraintRight_toRightOf="parent"
                app:layout_constraintTop_toTopOf="parent"
                app:layout_constraintVertical_bias="0.452" />

            <TextView
                android:id="@+id/vom"
                android:layout_width="match_parent"
                android:layout_height="wrap_content"
                android:gravity="center"
                android:text="Vomiting"
                android:background="#333"
                android:textColor="#fff"
                android:textSize="21sp" />

            <ImageButton
                android:id="@+id/unconscious"
                android:layout_width="match_parent"
                android:layout_height="115dp"
                android:layout_marginBottom="8dp"
                android:layout_marginEnd="8dp"
                android:layout_marginLeft="8dp"
                android:layout_marginRight="8dp"
                android:layout_marginStart="8dp"
                android:layout_marginTop="8dp"
                android:scaleType="centerCrop"
                android:src="@drawable/lost_conscious_icon"
                app:layout_constraintBottom_toBottomOf="parent"
                app:layout_constraintHorizontal_bias="0.774"
                app:layout_constraintLeft_toLeftOf="parent"
                app:layout_constraintRight_toRightOf="parent"
                app:layout_constraintTop_toTopOf="parent"
                app:layout_constraintVertical_bias="0.11" />

            <TextView
                android:id="@+id/unc"
                android:layout_width="match_parent"
                android:layout_height="wrap_content"
                android:gravity="center"
                android:text="Unconscious"
                android:background="#333"
                android:textColor="#fff"
                android:textSize="21sp" />

            <ImageButton
                android:id="@+id/fracture2"
                android:layout_width="match_parent"
                android:layout_height="115dp"
                android:layout_marginBottom="8dp"
                android:layout_marginEnd="8dp"
                android:layout_marginLeft="8dp"
                android:layout_marginRight="8dp"
                android:layout_marginStart="8dp"
                android:layout_marginTop="8dp"
                android:scaleType="centerCrop"
                android:src="@drawable/fracture_icon"
                app:layout_constraintBottom_toBottomOf="parent"
                app:layout_constraintHorizontal_bias="0.189"
                app:layout_constraintLeft_toLeftOf="parent"
                app:layout_constraintRight_toRightOf="parent"
                app:layout_constraintTop_toTopOf="parent"
                app:layout_constraintVertical_bias="0.794" />

            <TextView
                android:id="@+id/fra"
                android:layout_width="match_parent"
                android:layout_height="wrap_content"
                android:text="Fracture"
                android:gravity="center"
                android:background="#333"
                android:textColor="#fff"
                android:textSize="21sp" />

            <ImageButton
                android:id="@+id/dislocate2"
                android:layout_width="match_parent"
                android:layout_height="115dp"
                android:layout_marginBottom="8dp"
                android:layout_marginEnd="8dp"
                android:layout_marginLeft="8dp"
                android:layout_marginRight="8dp"
                android:layout_marginStart="8dp"
                android:layout_marginTop="8dp"
                android:scaleType="centerCrop"
                android:src="@drawable/dislocate_icon"
                app:layout_constraintBottom_toBottomOf="parent"
                app:layout_constraintHorizontal_bias="0.774"
                app:layout_constraintLeft_toLeftOf="parent"
                app:layout_constraintRight_toRightOf="parent"
                app:layout_constraintTop_toTopOf="parent"
                app:layout_constraintVertical_bias="0.452" />

            <TextView
                android:id="@+id/dis"
                android:layout_width="match_parent"
                android:layout_height="wrap_content"
                android:text="Dislocate"
                android:gravity="center"
                android:background="#333"
                android:textColor="#fff"
                android:textSize="21sp" />

            <ImageButton
                android:id="@+id/heart_attack2"
                android:layout_width="match_parent"
                android:layout_height="115dp"
                android:layout_marginBottom="8dp"
                android:layout_marginEnd="8dp"
                android:layout_marginLeft="8dp"
                android:layout_marginRight="8dp"
                android:layout_marginStart="8dp"
                android:layout_marginTop="8dp"
                android:scaleType="centerCrop"
                android:src="@drawable/heart_attack_icon"
                app:layout_constraintBottom_toBottomOf="parent"
                app:layout_constraintHorizontal_bias="0.774"
                app:layout_constraintLeft_toLeftOf="parent"
                app:layout_constraintRight_toRightOf="parent"
                app:layout_constraintTop_toTopOf="parent"
                app:layout_constraintVertical_bias="0.794" />

            <TextView
                android:id="@+id/hea"
                android:layout_width="match_parent"
                android:layout_height="wrap_content"
                android:text="Heart Attack"
                android:background="#333"
                android:textColor="#fff"
                android:gravity="center"
                android:textSize="21sp" />


        </LinearLayout>
    </ScrollView>
</android.support.constraint.ConstraintLayout>

Answer 1

这个问题可能是新来者提出的问题最多，Android Studio标签也无关紧要。如果您在Java或Android中获得NullPointerException，则可能无法使用new关键字或findViewById()或相关方法实例化视图或对象。简而言之，您的视图不会从xml文件中膨胀，并且在内存中有一个空指针。您应该在打开线程之前进行搜索，尤其是NullPointerException线程。

我的应用程序继续崩溃说＆＃34;已停止＆＃34;引起：java.lang.NullPointerException

1 个答案: