Question

我的目标是从评级栏中获取值，然后存储并显示值。

我的onClickMethod

中有以下代码

 rb = (RatingBar) findViewById(R.id.ratingBar);
    result = (TextView) findViewById(R.id.lblResult);

    rb.setOnRatingBarChangeListener(new RatingBar.OnRatingBarChangeListener() {
        @Override
        public void onRatingChanged(RatingBar ratingBar, float rating, boolean fromUser) {

        }
    });

它给了我这行的错误 rb.setOnRatingBarChangeListener(new RatingBar.OnRatingBarChangeListener()

logcat的：

11-19 18:12:10.328 8654-8654/tanav.sharma E/AndroidRuntime: FATAL EXCEPTION: main
Process: tanav.sharma, PID: 8654
java.lang.RuntimeException: Unable to start activity ComponentInfo{tanav.sharma/tanav.sharma.TanavActivity}: java.lang.NullPointerException: Attempt to invoke virtual method 'void android.widget.RatingBar.setOnRatingBarChangeListener(android.widget.RatingBar$OnRatingBarChangeListener)' on a null object reference
    at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:3319)
    at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:3415)
    at android.app.ActivityThread.access$1100(ActivityThread.java:229)
    at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1821)
    at android.os.Handler.dispatchMessage(Handler.java:102)
    at android.os.Looper.loop(Looper.java:148)
    at android.app.ActivityThread.main(ActivityThread.java:7331)
    at java.lang.reflect.Method.invoke(Native Method)
    at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:1230)
    at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:1120)
 Caused by: java.lang.NullPointerException: Attempt to invoke virtual method 'void android.widget.RatingBar.setOnRatingBarChangeListener(android.widget.RatingBar$OnRatingBarChangeListener)' on a null object reference
    at tanav.sharma.TanavActivity.onCreate(TanavActivity.java:101)
    at android.app.Activity.performCreate(Activity.java:6904)
    at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1136)
    at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:3266)
    at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:3415) 
    at android.app.ActivityThread.access$1100(ActivityThread.java:229) 
    at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1821) 
    at android.os.Handler.dispatchMessage(Handler.java:102) 
    at android.os.Looper.loop(Looper.java:148) 
    at android.app.ActivityThread.main(ActivityThread.java:7331) 
    at java.lang.reflect.Method.invoke(Native Method) 
    at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:1230) 
    at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:1120)

.XML

<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"
    android:padding="16dp"
    tools:context="tanav.sharma.OneFragment">

    <LinearLayout
        android:id="@+id/name_id"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:orientation="horizontal">

        <TextView
            android:layout_width="180dp"
            android:layout_height="wrap_content"
            android:text="@string/fname"
            android:textSize="20dp"
            android:textStyle="bold"
            android:layout_centerInParent="true"/>

        <TextView
            android:layout_width="140dp"
            android:layout_height="wrap_content"
            android:text="@string/sid"
            android:textAlignment="textEnd"
            android:textSize="20dp"
            android:textStyle="bold"
            android:layout_centerInParent="true"/>
    </LinearLayout>

    <LinearLayout
        android:padding="16dp"
        android:id="@+id/counter_display"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:orientation="horizontal"
        android:layout_below="@+id/name_id">

        <TextView
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:text="Counter: "
            android:layout_gravity="left|center_vertical" />

        <TextView
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:text=""
            android:id="@+id/counter"
            />

    </LinearLayout>

    <LinearLayout
        android:id="@+id/five_star"
        android:padding="10dp"
        android:layout_centerHorizontal="true"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_below="@+id/counter_display">

        <RatingBar
            android:id="@+id/ratingBar"
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:numStars="5"
            android:stepSize="0.5"
            android:rating="5.0"
            />

    </LinearLayout>

    <RelativeLayout
        android:id="@+id/download_button"
        android:layout_below="@+id/five_star"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        >

        <Button
            android:layout_width="match_parent"
            android:layout_height="wrap_content"
            android:id="@+id/download_image"
            android:text="@string/download"
            />

        <ImageView
            android:layout_width="match_parent"
            android:layout_height="wrap_content" />


    </RelativeLayout>




</RelativeLayout>

以下文件是.java文件（即MainActivity.java）

public class TanavActivity extends AppCompatActivity {

    RatingBar rb;
    TextView result;

    private Toolbar toolbar;
    private TabLayout tabLayout;
    private ViewPager viewPager;
    private int[] tabIcons = {
            R.drawable.ic_action_pro,
            R.drawable.ic_action_web
    };

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


        toolbar = (Toolbar)findViewById(R.id.toolbar);
        setSupportActionBar(toolbar);

        /**
         * This button is responsible for taking the user back
         * to the main activity. Preventing the user from pressing
         * the back key multiple times.
         */
        getSupportActionBar().setDisplayHomeAsUpEnabled(true);

        viewPager = (ViewPager)findViewById(R.id.viewpager);
        setupViewPager(viewPager);

        tabLayout = (TabLayout)findViewById(R.id.tabs);
        tabLayout.setupWithViewPager(viewPager);
        setupTabIcons();

        tabLayout.addOnTabSelectedListener(new TabLayout.OnTabSelectedListener() {

            int count_image = 0;
            int count_web = 0;
            @Override
            public void onTabSelected(TabLayout.Tab tab) {
                int position = tab.getPosition();
                if(position == 0){

                    count_image = count_image + 1;
                    TextView counter = (TextView) findViewById(R.id.counter);
                    counter.setText(Integer.toString(count_image));

                }else if(position == 1){
                    //count_web = count_web + 1;
                }
            }

            @Override
            public void onTabUnselected(TabLayout.Tab tab) {

            }

            @Override
            public void onTabReselected(TabLayout.Tab tab) {
                count_image = count_image + 1;
                TextView counter = (TextView) findViewById(R.id.counter);
                counter.setText(Integer.toString(count_image));
            }
        });

        rb = (RatingBar) findViewById(R.id.ratingBar);
        result = (TextView) findViewById(R.id.lblResult);

        rb.setOnRatingBarChangeListener(new RatingBar.OnRatingBarChangeListener() {
            @Override
            public void onRatingChanged(RatingBar ratingBar, float rating, boolean fromUser) {

            }
        });

    }

Answer 1

一切似乎都是对的。您的内容视图一定有问题。确保这是你的xml。使用具有ratingBar id的xml文件名更改它。

setContentView(R.layout.activity_tanav);

setOnRatingBarChangeListener上的ratingBar运行时错误

1 个答案: