java - 为什么 onClickListener 在我启动应用程序时会使它崩溃？

Question

我是一名新程序员，尝试在按下启动屏幕上的按钮时加载新 View 。我的启动项是一个具有 4 个 View 的 viewPager。我在这些 View 上有一个按钮，按下该按钮时我想要加载 ListView View 。但是当我添加 onClickListener 时，应用程序启动后它就会崩溃。这几天我一直在试图解决这个问题，现在我真的很绝望!提前致谢。

我试图找出致命异常 MAIN 的含义，但似乎每个程序都有不同的问题。

public class Splash extends Activity {

ImageButton listButton;

@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    requestWindowFeature(Window.FEATURE_NO_TITLE);
    getWindow().setFlags(WindowManager.LayoutParams.FLAG_FULLSCREEN,
            WindowManager.LayoutParams.FLAG_FULLSCREEN);
    setContentView(R.layout.splash);

    SplashPager adapter = new SplashPager();
    ViewPager myPager = (ViewPager) findViewById(R.id.splashPager);
    myPager.setAdapter(adapter);
    myPager.setCurrentItem(0);

    listButtonListener();
}

public void listButtonListener() {
    listButton = (ImageButton) findViewById(R.id.splashB);
    listButton.setOnClickListener(new OnClickListener() {
        @Override
        public void onClick(View arg0) {
            startActivity(new Intent("com.example.survtest1.Main"));
        }
    });
}
}

//崩溃日志

01-14 22:12:32.069: W/dalvikvm(14733): threadid=1: thread exiting with uncaught exception (group=0x40207560)
01-14 22:12:32.079: E/AndroidRuntime(14733): FATAL EXCEPTION: main
01-14 22:12:32.079: E/AndroidRuntime(14733): java.lang.RuntimeException: Unable to start activity ComponentInfo{com.example.survtest1/com.example.survtest1.Splash}: java.lang.NullPointerException
01-14 22:12:32.079: E/AndroidRuntime(14733):    at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:1658)
01-14 22:12:32.079: E/AndroidRuntime(14733):    at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:1674)
01-14 22:12:32.079: E/AndroidRuntime(14733):    at android.app.ActivityThread.access$1500(ActivityThread.java:117)
01-14 22:12:32.079: E/AndroidRuntime(14733):    at android.app.ActivityThread$H.handleMessage(ActivityThread.java:942)
01-14 22:12:32.079: E/AndroidRuntime(14733):    at android.os.Handler.dispatchMessage(Handler.java:99)
01-14 22:12:32.079: E/AndroidRuntime(14733):    at android.os.Looper.loop(Looper.java:130)
01-14 22:12:32.079: E/AndroidRuntime(14733):    at android.app.ActivityThread.main(ActivityThread.java:3733)
01-14 22:12:32.079: E/AndroidRuntime(14733):    at java.lang.reflect.Method.invokeNative(Native Method)
01-14 22:12:32.079: E/AndroidRuntime(14733):    at java.lang.reflect.Method.invoke(Method.java:507)
01-14 22:12:32.079: E/AndroidRuntime(14733):    at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:892)
01-14 22:12:32.079: E/AndroidRuntime(14733):    at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:650)
01-14 22:12:32.079: E/AndroidRuntime(14733):    at dalvik.system.NativeStart.main(Native Method)
01-14 22:12:32.079: E/AndroidRuntime(14733): Caused by: java.lang.NullPointerException
01-14 22:12:32.079: E/AndroidRuntime(14733):    at com.example.survtest1.Splash.listButtonListener(Splash.java:40)
01-14 22:12:32.079: E/AndroidRuntime(14733):    at com.example.survtest1.Splash.onCreate(Splash.java:31)
01-14 22:12:32.079: E/AndroidRuntime(14733):    at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1047)
01-14 22:12:32.079: E/AndroidRuntime(14733):    at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:1622)
01-14 22:12:32.079: E/AndroidRuntime(14733):    ... 11 more
01-14 22:12:32.079: E/AndroidRuntime(14733): [Blue Error Handler] Make Debugging Report file for main
01-14 22:12:32.079: E/AndroidRuntime(14733): java.lang.RuntimeException: Unable to start activity ComponentInfo{com.example.survtest1/com.example.survtest1.Splash}: java.lang.NullPointerException
01-14 22:12:32.079: E/AndroidRuntime(14733):    at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:1658)
01-14 22:12:32.079: E/AndroidRuntime(14733):    at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:1674)
01-14 22:12:32.079: E/AndroidRuntime(14733):    at android.app.ActivityThread.access$1500(ActivityThread.java:117)
01-14 22:12:32.079: E/AndroidRuntime(14733):    at android.app.ActivityThread$H.handleMessage(ActivityThread.java:942)
01-14 22:12:32.079: E/AndroidRuntime(14733):    at android.os.Handler.dispatchMessage(Handler.java:99)
01-14 22:12:32.079: E/AndroidRuntime(14733):    at android.os.Looper.loop(Looper.java:130)
01-14 22:12:32.079: E/AndroidRuntime(14733):    at android.app.ActivityThread.main(ActivityThread.java:3733)
01-14 22:12:32.079: E/AndroidRuntime(14733):    at java.lang.reflect.Method.invokeNative(Native Method)
01-14 22:12:32.079: E/AndroidRuntime(14733):    at java.lang.reflect.Method.invoke(Method.java:507)
01-14 22:12:32.079: E/AndroidRuntime(14733):    at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:892)
01-14 22:12:32.079: E/AndroidRuntime(14733):    at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:650)
01-14 22:12:32.079: E/AndroidRuntime(14733):    at dalvik.system.NativeStart.main(Native Method)
01-14 22:12:32.079: E/AndroidRuntime(14733): Caused by: java.lang.NullPointerException
01-14 22:12:32.079: E/AndroidRuntime(14733):    at com.example.survtest1.Splash.listButtonListener(Splash.java:40)
01-14 22:12:32.079: E/AndroidRuntime(14733):    at com.example.survtest1.Splash.onCreate(Splash.java:31)
01-14 22:12:32.079: E/AndroidRuntime(14733):    at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1047)
01-14 22:12:32.079: E/AndroidRuntime(14733):    at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:1622)
01-14 22:12:32.079: E/AndroidRuntime(14733):    ... 11 more

// list

<application
    android:allowBackup="true"
    android:icon="@drawable/ic_launcher"
    android:label="@string/app_name"
    android:theme="@style/AppTheme" >
    <activity
        android:name="com.example.survtest1.Splash"
        android:label="@string/app_name" >
        <intent-filter>
            <action android:name="android.intent.action.MAIN" />

            <category android:name="android.intent.category.LAUNCHER" />
        </intent-filter>
    </activity>
    <activity
        android:name="com.example.survtest1.Main"
        android:label="@string/app_name" >
        <intent-filter>
            <action android:name="android.intent.action.MAIN" />

            <category android:name="android.intent.category.LAUNCHER" />
        </intent-filter>
    </activity>
</application>

//xml布局

<?xml version="1.0" encoding="utf-8"?>
<FrameLayout 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/splash" 
android:background="#000000" >

<ImageView

    android:layout_width="wrap_content"
    android:layout_height="wrap_content"
    android:layout_gravity="center_horizontal"
    android:src="@drawable/intro__1" />

   <Button
       android:layout_width="wrap_content"
       android:layout_height="wrap_content"
       android:text="aaaaaaaaaaaaaaaaaa" 
       android:layout_gravity="bottom" 
       android:layout_marginLeft="75dp"
       android:id="@+id/splashB" 
       android:onClick="startActivity" />

</FrameLayout>

我刚刚尝试添加 android:onClick 但它仍然崩溃

Answer 1

您的问题是这样的:

01-14 22:12:32.079: E/AndroidRuntime(14733): Caused by: java.lang.NullPointerException
01-14 22:12:32.079: E/AndroidRuntime(14733):    at com.example.survtest1.Splash.listButtonListener(Splash.java:40)

如果我猜测(因为您没有粘贴 Activity 的完整源代码，我不确定哪一行是第 40 行)，我会说您的错误在这一行:

listButton = (ImageButton) findViewById(R.id.splashB);

具体来说，您的布局很可能丢失 <ImageButton android:id="@+id/splashB" ...>元素。因此，您的listButton为 null，结果为 NullPointerException在下一行。

更新:您的应用程序崩溃是因为，虽然它确实有 <Button> ID 为splashB ，该按钮不是 <ImageButton> ，这就是您的代码所期望的。

您必须更改布局才能使用 <ImageButton>或更改此行:

listButton = (ImageButton) findViewById(R.id.splashB);

至:

listButton = (Button) findViewById(R.id.splashB);

两者都应该有效。