java.lang.nullpointerexception错误：app崩溃

Question

我按下激活我的单选按钮所在的xml的按钮后，我的应用程序崩溃了。

logcat说我的错误是java.lang.nullpointerexception。

我已经包含了我的logcat，发生错误的java和manifest。

我最初遇到了RadioButtons的问题，程序允许我检查它们并且无法取消选中。当我改变编码以包含onCheckChange监听器时，只要按RadioButton，应用就会崩溃。

07-17 18:09:37.067: W/dalvikvm(329): threadid=1: thread exiting with uncaught exception (group=0x40015560)
07-17 18:09:37.077: E/AndroidRuntime(329): FATAL EXCEPTION: main
07-17 18:09:37.077: E/AndroidRuntime(329): java.lang.RuntimeException: Unable to instantiate activity ComponentInfo{com.example.com.proto1/com.example.com.proto1.Voiceprompt}: java.lang.ClassNotFoundException: com.example.com.proto1.Voiceprompt in loader dalvik.system.PathClassLoader[/data/app/com.example.com.proto1-2.apk]
07-17 18:09:37.077: E/AndroidRuntime(329):  at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:1569)
07-17 18:09:37.077: E/AndroidRuntime(329):  at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:1663)
07-17 18:09:37.077: E/AndroidRuntime(329):  at android.app.ActivityThread.access$1500(ActivityThread.java:117)
07-17 18:09:37.077: E/AndroidRuntime(329):  at android.app.ActivityThread$H.handleMessage(ActivityThread.java:931)
07-17 18:09:37.077: E/AndroidRuntime(329):  at android.os.Handler.dispatchMessage(Handler.java:99)
07-17 18:09:37.077: E/AndroidRuntime(329):  at android.os.Looper.loop(Looper.java:123)
07-17 18:09:37.077: E/AndroidRuntime(329):  at android.app.ActivityThread.main(ActivityThread.java:3683)
07-17 18:09:37.077: E/AndroidRuntime(329):  at java.lang.reflect.Method.invokeNative(Native Method)
07-17 18:09:37.077: E/AndroidRuntime(329):  at java.lang.reflect.Method.invoke(Method.java:507)
07-17 18:09:37.077: E/AndroidRuntime(329):  at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:839)
07-17 18:09:37.077: E/AndroidRuntime(329):  at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:597)
07-17 18:09:37.077: E/AndroidRuntime(329):  at dalvik.system.NativeStart.main(Native Method)
07-17 18:09:37.077: E/AndroidRuntime(329): Caused by: java.lang.ClassNotFoundException: com.example.com.proto1.Voiceprompt in loader dalvik.system.PathClassLoader[/data/app/com.example.com.proto1-2.apk]
07-17 18:09:37.077: E/AndroidRuntime(329):  at dalvik.system.PathClassLoader.findClass(PathClassLoader.java:240)
07-17 18:09:37.077: E/AndroidRuntime(329):  at java.lang.ClassLoader.loadClass(ClassLoader.java:551)
07-17 18:09:37.077: E/AndroidRuntime(329):  at java.lang.ClassLoader.loadClass(ClassLoader.java:511)
07-17 18:09:37.077: E/AndroidRuntime(329):  at android.app.Instrumentation.newActivity(Instrumentation.java:1021)
07-17 18:09:37.077: E/AndroidRuntime(329):  at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:1561)
07-17 18:09:37.077: E/AndroidRuntime(329):  ... 11 more


    package com.example.com.proto1;

import android.app.Activity;
import android.content.Intent;
import android.media.MediaPlayer;
import android.os.Bundle;
import android.view.View;
import android.widget.RadioButton;
import android.widget.RadioGroup;
import android.widget.RadioGroup.OnCheckedChangeListener;

public class VoicePrompts extends Activity implements OnCheckedChangeListener {

    RadioButton on, off, onc, offc;

    // Button Sound
    MediaPlayer buttonSound1 = MediaPlayer.create(VoicePrompts.this, R.raw.vpo);
    MediaPlayer buttonSound2 = MediaPlayer
            .create(VoicePrompts.this, R.raw.vpof);
    MediaPlayer buttonSound3 = MediaPlayer
            .create(VoicePrompts.this, R.raw.vpoc);
    MediaPlayer buttonSound4 = MediaPlayer.create(VoicePrompts.this,
            R.raw.vpofc);

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        // TODO Auto-generated method stub
        super.onCreate(savedInstanceState);
        setContentView(R.layout.voiceprompts);

        // Setting up the button references
        on = (RadioButton) findViewById(R.id.vbutton1);
        off = (RadioButton) findViewById(R.id.vbutton2);
        onc = (RadioButton) findViewById(R.id.vbutton1);
        offc = (RadioButton) findViewById(R.id.vbutton2);

        buttonSound1 = MediaPlayer.create(VoicePrompts.this, R.raw.vpo);
        buttonSound2 = MediaPlayer.create(VoicePrompts.this, R.raw.vpof);
        buttonSound3 = MediaPlayer.create(VoicePrompts.this, R.raw.vpoc);
        buttonSound4 = MediaPlayer.create(VoicePrompts.this, R.raw.vpofc);
    }

    public void onCheckedChanged(RadioGroup arg0, int checkedId) {
        // TODO Auto-generated method stub
        switch (checkedId) {
        case R.id.vbutton1:
            on.setOnLongClickListener(new View.OnLongClickListener() {

                public boolean onLongClick(View v) {
                    // TODO Auto-generated method stub
                    try {
                        buttonSound1.prepare();
                        buttonSound1.start();
                        startActivity(new Intent("android.intent.action.VPON"));

                    } catch (Exception e) {

                    }
                    return false;
                }
            });

            onc.setOnClickListener(new View.OnClickListener() {

                public void onClick(View v) {
                    // TODO Auto-generated method stub
                    try {
                        buttonSound3.prepare();
                        buttonSound3.start();
                        startActivity(new Intent("android.intent.action.VPON"));
                    } catch (Exception e) {

                    }
                    ;

                }
            });

            break;
        case R.id.vbutton2:

            off.setOnLongClickListener(new View.OnLongClickListener() {

                public boolean onLongClick(View v) {
                    // TODO Auto-generated method stub
                    try {
                        buttonSound2.prepare();
                        buttonSound2.start();
                        startActivity(new Intent("android.intent.action.VPOFF"));
                    } catch (Exception e) {

                    }
                    ;
                    return false;

                }
            });

            offc.setOnClickListener(new View.OnClickListener() {

                public void onClick(View v) {
                    // TODO Auto-generated method stub
                    try {
                        buttonSound4.prepare();
                        buttonSound4.start();
                        startActivity(new Intent("android.intent.action.VPOFF"));
                    } catch (Exception e) {

                    }
                    ;

                }
            });

            break;
        }

    }

}




<manifest xmlns:android="http://schemas.android.com/apk/res/android"
    package="com.example.com.proto1"
    android:versionCode="1"
    android:versionName="1.0" >

    <uses-sdk
        android:minSdkVersion="8"
        android:targetSdkVersion="15" />

    <application
        android:icon="@drawable/ic_launcher"
        android:label="@string/app_name"
        android:theme="@style/AppTheme" >
        <activity
            android:name=".mainj"
            android:label="@string/title_activity_mainj" >
            <intent-filter>
                <action android:name="android.intent.action.MAIN" />

                <category android:name="android.intent.category.LAUNCHER" />
            </intent-filter>
        </activity>
        <activity
            android:name=".menu"
            android:label="@string/app_name" >
            <intent-filter>
                <action android:name="android.intent.action.MENU" />

                <category android:name="android.intent.category.DEFAULT" />
            </intent-filter>
        </activity>
        <activity
            android:name=".Infoactive"
            android:label="@string/app_name" >
            <intent-filter>
                <action android:name="android.intent.action.INFOSCREEN" />

                <category android:name="android.intent.category.DEFAULT" />
            </intent-filter>
        </activity>
        <activity
            android:name=".VoicePrompts"
            android:label="@string/app_name" >
            <intent-filter>
                <action android:name="android.intent.action.VOICEPROMPTS" />

                <category android:name="android.intent.category.DEFAULT" />
            </intent-filter>
        </activity>
        <activity
            android:name=".VPon"
            android:label="@string/app_name" >
            <intent-filter>
                <action android:name="android.intent.action.VPON" />

                <category android:name="android.intent.category.DEFAULT" />
            </intent-filter>
        </activity>
        <activity
            android:name=".VPoff"
            android:label="@string/app_name" >
            <intent-filter>
                <action android:name="android.intent.action.VPOFF" />

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

</manifest>





package com.example.com.proto1;

import android.app.Activity;
import android.content.Intent;
import android.media.MediaPlayer;
import android.os.Bundle;
import android.view.View;
import android.widget.Button;

public class menu extends Activity {

    @Override
    protected void onCreate(Bundle aboutmenu) {
        // TODO Auto-generated method stub
        super.onCreate(aboutmenu);
        setContentView(R.layout.mainx);

        // Button Sound
        final MediaPlayer buttonSound = MediaPlayer.create(menu.this,
                R.raw.button_click);

        // Setting up the button references
        Button info = (Button) findViewById(R.id.aboutbutton);
        Button voice = (Button) findViewById(R.id.voicebutton);

        info.setOnClickListener(new View.OnClickListener() {

            public void onClick(View v) {
                // TODO Auto-generated method stub
                buttonSound.start();
                startActivity(new Intent("android.intent.action.INFOSCREEN"));

            }
        });

        voice.setOnClickListener(new View.OnClickListener() {

            public void onClick(View v) {
                // TODO Auto-generated method stub
                buttonSound.start();
                Intent voiceIntent = new Intent("android.intent.action.VOICEPROMPTS");
                startActivity(voiceIntent);
            }
        });

    }
}

Answer 1

在setContentView(R.layout.voiceprompts);

之后提供按钮引用

<强>像，

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

         // Setting up the button references

            on = (RadioButton) findViewById(R.id.vbutton1);
            off = (RadioButton) findViewById(R.id.vbutton2);
            onc = (RadioButton) findViewById(R.id.vbutton1);
            offc = (RadioButton) findViewById(R.id.vbutton2);
    }

Answer 2

我认为您有两个名为VoicePrompts和VoicePrompt的活动。您在清单文件中声明了VoicePrompts。但是你打电话给VoicePrompt。

编辑根据您的新问题

MediaPlayer buttonSound1，buttonSound2，buttonSound3，buttonSound4;

并在onCreate

中初始化

像

 @Override
protected void onCreate(Bundle savedInstanceState) {
    // TODO Auto-generated method stub
    super.onCreate(savedInstanceState);
    setContentView(R.layout.voiceprompts);

    // Setting up the button references
    on = (RadioButton) findViewById(R.id.vbutton1);
    off = (RadioButton) findViewById(R.id.vbutton2);
    onc = (RadioButton) findViewById(R.id.vbutton1);
    offc = (RadioButton) findViewById(R.id.vbutton2);
    buttonSound1 = MediaPlayer.create(VoicePrompts.this,
        R.raw.vpo);
    buttonSound2 = MediaPlayer.create(VoicePrompts.this,
        R.raw.vpof);
    buttonSound3 = MediaPlayer.create(VoicePrompts.this,
        R.raw.vpoc);
    buttonSound4 = MediaPlayer.create(VoicePrompts.this,
        R.raw.vpofc);
}