java - 开发一个似乎因无法调用虚拟方法而不断崩溃的应用程序

Question

所以我正在尝试构建一个讲故事的应用程序，但它似乎一直在崩溃，而且我还没有找到解决问题的方法。我认为这是由于我的名为 Page 的数组类或尝试从我的资源调用可绘制对象时出现问题。

我已经尝试重新编写我的整个代码，更改我所知道的任何值。

这是我创建数组来保存我的 vaules 的类(class)之一，我使用构造函数将故事内容更好地放入数组中。

public class Story {

    private Page[] pages;

    public Story(){
        pages = new Page[7];

       pages[0] = new Page(R.drawable.page0,
               R.string.page0,
               new Choice(R.string.page0_choice1,1),
               new Choice(R.string.page0_choice2,2));
        pages[1] = new Page(R.drawable.page1,
                R.string.page1,
                new Choice(R.string.page1_choice1, 3),
                new Choice(R.string.page1_choice2, 4));

        pages[2] = new Page(R.drawable.page2,
                R.string.page2,
                new Choice(R.string.page2_choice1, 4),
                new Choice(R.string.page2_choice2, 6));

        pages[3] = new Page(R.drawable.page3,
                R.string.page3,
                new Choice(R.string.page3_choice1, 4),
                new Choice(R.string.page3_choice2, 5));

        pages[4] = new Page(R.drawable.page4,
                R.string.page4,
                new Choice(R.string.page4_choice1, 5),
                new Choice(R.string.page4_choice2, 6));

        pages[5] = new Page(R.drawable.page5, R.string.page5);

        pages[6] = new Page(R.drawable.page6, R.string.page6);
    }

    public Page getPage(int pageNumber) {
        if(pageNumber >= pages.length) {
            pageNumber = 0;
        }
        return pages[pageNumber];

这是另一个包含我的代码的类，它似乎是我的错误来源，我最常尝试弄乱这个类。

public class StoryActivity extends AppCompatActivity {

    public static final String TAG = StoryActivity.class.getSimpleName();

    private Story story;
    public ImageView storyImageView;
    private TextView storyTextView;
    private Button choice1Button;
    private Button choice2Button;

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

        storyImageView = (ImageView)findViewById(R.id.storyImageView);
        storyTextView = (TextView)findViewById(R.id.storyTextView);
        choice1Button = (Button)findViewById(R.id.choice1Button);
        choice2Button = (Button)findViewById(R.id.choice2Button);

        // get the intent used to start this activity

        Intent intent = getIntent();
        String name = intent.getStringExtra(getString(R.string.key_name));
        if (name == null || name.isEmpty()) {
            name = "Friend";
        }
        Log.d(TAG, name);

        story = new Story();
        loadPage(0);


    }

    private void loadPage(int pageNumber) {
        Page page = story.getPage(pageNumber);

        Drawable image = ContextCompat.getDrawable(this, page.getImageId());
        storyImageView.setImageDrawable(image);

    }
}

我希望应用程序能够按下一个按钮而不会崩溃 我从崩溃日志中得到的消息是。

2019-07-25 00:02:39.729 4655-4655/com.thomas.interactivestory E/AndroidRuntime: FATAL EXCEPTION: main
    Process: com.thomas.interactivestory, PID: 4655
    java.lang.RuntimeException: Unable to start activity ComponentInfo{com.thomas.interactivestory/com.thomas.interactivestory.ui.StoryActivity}: java.lang.NullPointerException: Attempt to invoke virtual method 'void android.widget.ImageView.setImageDrawable(android.graphics.drawable.Drawable)' on a null object reference
        at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2665)
        at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2726)
        at android.app.ActivityThread.-wrap12(ActivityThread.java)
        at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1477)
        at android.os.Handler.dispatchMessage(Handler.java:102)
        at android.os.Looper.loop(Looper.java:154)
        at android.app.ActivityThread.main(ActivityThread.java:6119)
        at java.lang.reflect.Method.invoke(Native Method)
        at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:886)
        at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:776)
     Caused by: java.lang.NullPointerException: Attempt to invoke virtual method 'void android.widget.ImageView.setImageDrawable(android.graphics.drawable.Drawable)' on a null object reference
        at com.thomas.interactivestory.ui.StoryActivity.loadPage(StoryActivity.java:58)
        at com.thomas.interactivestory.ui.StoryActivity.onCreate(StoryActivity.java:49)
        at android.app.Activity.performCreate(Activity.java:6679)
        at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1118)
        at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2618)
        at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2726) 
        at android.app.ActivityThread.-wrap12(ActivityThread.java) 
        at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1477) 
        at android.os.Handler.dispatchMessage(Handler.java:102) 
        at android.os.Looper.loop(Looper.java:154) 
        at android.app.ActivityThread.main(ActivityThread.java:6119) 
        at java.lang.reflect.Method.invoke(Native Method) 
        at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:886) 
        at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:776)

这是我的 activity_Main.xml 文件，希望对您有所帮助

<?xml version="1.0" encoding="utf-8"?>
<androidx.constraintlayout.widget.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"
    android:background="@android:color/white"
    tools:context="com.thomas.interactivestory.ui.MainActivity">

    <ImageView
        android:id="@+id/titleImageView"
        android:layout_width="0dp"
        android:layout_height="wrap_content"
        android:adjustViewBounds="true"
        android:contentDescription="@string/signals_from_mars_title_image"
        android:cropToPadding="true"
        android:scaleType="fitXY"
        app:layout_constraintEnd_toEndOf="parent"
        app:layout_constraintStart_toStartOf="parent"
        app:layout_constraintTop_toTopOf="parent"
        android:layout_marginTop="0dp"
        app:srcCompat="@drawable/main_title" />

    <Button
        android:id="@+id/StartButton"
        android:layout_width="0dp"
        android:layout_marginBottom="0dp"
        android:layout_marginLeft="0dp"
        android:layout_marginRight="0dp"
        android:layout_height="wrap_content"
        android:background="@android:color/white"
        android:text="@string/start_your_adventure"
        android:textColor="#2A8AEC"
        android:textSize="16sp"
        app:layout_constraintHorizontal_bias="0.0"
        app:layout_constraintBottom_toBottomOf="parent"
        app:layout_constraintEnd_toEndOf="parent"
        app:layout_constraintStart_toStartOf="parent" />

    <EditText
        android:id="@+id/NameEditText"
        android:layout_width="0dp"
        android:layout_height="wrap_content"
        android:layout_marginBottom="0dp"
        android:layout_marginLeft="0dp"
        android:layout_marginRight="0dp"
        android:includeFontPadding="true"
        android:ems="10"
        android:hint="@string/enter_your_name"
        android:inputType="textPersonName|textCapWords"
        android:maxLength="30"
        app:layout_constraintBottom_toTopOf="@+id/StartButton"
        app:layout_constraintEnd_toEndOf="parent"
        app:layout_constraintStart_toStartOf="parent" />

</androidx.constraintlayout.widget.ConstraintLayout>

Answer 1

您的 activity_main.xml 缺少 storyImageView。