Question

我知道有很多人有这个问题。我已经尝试了很多方法，但是仍然会遇到错误。

只有一项活动而且已经注册。
尝试通过com.hermione.woodenfish.MainActivity完成.MainActivity，没有用
清理和重建不起作用

真的需要帮助，谢谢!!

logcat的：

08-01 12:09:33.944: E/Trace(1032): error opening trace file: No such file or directory (2)
08-01 12:09:34.384: D/AndroidRuntime(1032): Shutting down VM
08-01 12:09:34.424: W/dalvikvm(1032): threadid=1: thread exiting with uncaught exception (group=0x40a13300)
08-01 12:09:34.465: E/AndroidRuntime(1032): FATAL EXCEPTION: main
08-01 12:09:34.465: E/AndroidRuntime(1032): java.lang.RuntimeException: Unable to     instantiate activity   ComponentInfo{com.hermione.woodenfish/com.hermione.woodenfish.MainActivity}: java.lang.NullPointerException
08-01 12:09:34.465: E/AndroidRuntime(1032):     at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:1983)
08-01 12:09:34.465: E/AndroidRuntime(1032):     at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2084)
08-01 12:09:34.465: E/AndroidRuntime(1032):     at android.app.ActivityThread.access$600(ActivityThread.java:130)
08-01 12:09:34.465: E/AndroidRuntime(1032):     at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1195)
08-01 12:09:34.465: E/AndroidRuntime(1032):     at android.os.Handler.dispatchMessage(Handler.java:99)
08-01 12:09:34.465: E/AndroidRuntime(1032):     at android.os.Looper.loop(Looper.java:137)
08-01 12:09:34.465: E/AndroidRuntime(1032):     at android.app.ActivityThread.main(ActivityThread.java:4745)
08-01 12:09:34.465: E/AndroidRuntime(1032):     at java.lang.reflect.Method.invokeNative(Native Method)
08-01 12:09:34.465: E/AndroidRuntime(1032):     at java.lang.reflect.Method.invoke(Method.java:511)
08-01 12:09:34.465: E/AndroidRuntime(1032):     at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:786)
08-01 12:09:34.465: E/AndroidRuntime(1032):     at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:553)
08-01 12:09:34.465: E/AndroidRuntime(1032):     at dalvik.system.NativeStart.main(Native Method)
08-01 12:09:34.465: E/AndroidRuntime(1032): Caused by: java.lang.NullPointerException
08-01 12:09:34.465: E/AndroidRuntime(1032):     at android.content.ContextWrapper.getResources(ContextWrapper.java:81)
08-01 12:09:34.465: E/AndroidRuntime(1032):     at android.media.MediaPlayer.create(MediaPlayer.java:824)
08-01 12:09:34.465: E/AndroidRuntime(1032):     at com.hermione.woodenfish.MainActivity.<init>(MainActivity.java:24)
08-01 12:09:34.465: E/AndroidRuntime(1032):     at java.lang.Class.newInstanceImpl(Native Method)
08-01 12:09:34.465: E/AndroidRuntime(1032):     at java.lang.Class.newInstance(Class.java:1319)
08-01 12:09:34.465: E/AndroidRuntime(1032):     at android.app.Instrumentation.newActivity(Instrumentation.java:1053)
08-01 12:09:34.465: E/AndroidRuntime(1032):     at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:1974)
08-01 12:09:34.465: E/AndroidRuntime(1032):     ... 11 more
08-01 12:33:02.784: E/Trace(1171): error opening trace file: No such file or directory (2)
08-01 12:33:03.125: D/AndroidRuntime(1171): Shutting down VM
08-01 12:33:03.125: W/dalvikvm(1171): threadid=1: thread exiting with uncaught exception (group=0x40a13300)
08-01 12:33:03.154: E/AndroidRuntime(1171): FATAL EXCEPTION: main
08-01 12:33:03.154: E/AndroidRuntime(1171): java.lang.RuntimeException: Unable to instantiate activity ComponentInfo{com.hermione.woodenfish/com.hermione.woodenfish.MainActivity}: java.lang.NullPointerException
08-01 12:33:03.154: E/AndroidRuntime(1171):     at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:1983)
08-01 12:33:03.154: E/AndroidRuntime(1171):     at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2084)
08-01 12:33:03.154: E/AndroidRuntime(1171):     at android.app.ActivityThread.access$600(ActivityThread.java:130)
08-01 12:33:03.154: E/AndroidRuntime(1171):     at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1195)
08-01 12:33:03.154: E/AndroidRuntime(1171):     at android.os.Handler.dispatchMessage(Handler.java:99)
08-01 12:33:03.154: E/AndroidRuntime(1171):     at android.os.Looper.loop(Looper.java:137)
08-01 12:33:03.154: E/AndroidRuntime(1171):     at android.app.ActivityThread.main(ActivityThread.java:4745)
08-01 12:33:03.154: E/AndroidRuntime(1171):     at java.lang.reflect.Method.invokeNative(Native Method)
08-01 12:33:03.154: E/AndroidRuntime(1171):     at java.lang.reflect.Method.invoke(Method.java:511)
08-01 12:33:03.154: E/AndroidRuntime(1171):     at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:786)
08-01 12:33:03.154: E/AndroidRuntime(1171):     at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:553)
08-01 12:33:03.154: E/AndroidRuntime(1171):     at dalvik.system.NativeStart.main(Native Method)
08-01 12:33:03.154: E/AndroidRuntime(1171): Caused by: java.lang.NullPointerException
08-01 12:33:03.154: E/AndroidRuntime(1171):     at android.content.ContextWrapper.getResources(ContextWrapper.java:81)
08-01 12:33:03.154: E/AndroidRuntime(1171):     at android.media.MediaPlayer.create(MediaPlayer.java:824)
08-01 12:33:03.154: E/AndroidRuntime(1171):     at com.hermione.woodenfish.MainActivity.<init>(MainActivity.java:23)
08-01 12:33:03.154: E/AndroidRuntime(1171):     at java.lang.Class.newInstanceImpl(Native Method)
08-01 12:33:03.154: E/AndroidRuntime(1171):     at java.lang.Class.newInstance(Class.java:1319)
08-01 12:33:03.154: E/AndroidRuntime(1171):     at android.app.Instrumentation.newActivity(Instrumentation.java:1053)
08-01 12:33:03.154: E/AndroidRuntime(1171):     at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:1974)
08-01 12:33:03.154: E/AndroidRuntime(1171):     ... 11 more

MainActivity.java

package com.hermione.woodenfish;

import android.app.Activity;
import android.media.MediaPlayer;
import android.os.Bundle;
import android.view.Menu;
import android.view.View;

public class MainActivity extends Activity {

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

    @Override
    public boolean onCreateOptionsMenu(Menu menu) {
        getMenuInflater().inflate(R.menu.activity_main, menu);
        return true;
    }

    private MediaPlayer mp = MediaPlayer.create(this, R.raw.knok);
    public void sendKnok(View view) {
        if (mp.isPlaying()){
            mp.stop();
        }
        mp.start();
    }
}

清单：

<manifest xmlns:android="http://schemas.android.com/apk/res/android"
    package="com.hermione.woodenfish"
    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=".MainActivity"
            android:label="@string/title_activity_main" >
            <intent-filter>
                <action android:name="android.intent.action.MAIN" />

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

</manifest>

Answer 1

我认为问题出在这一行，

 private MediaPlayer mp = MediaPlayer.create(this, R.raw.knok);

您已尝试在onCreate()之前初始化Context对象。这可能会造成问题。你怎么样在你的onCreate（）中初始化你的MediaPlayer，

private MediaPlayer mp =null;  //Global Declaration

@Override
public void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
    mp = MediaPlayer.create(this, R.raw.knok);
}

Answer 2

你的问题在这里：

08-01 12:33:03.154: E/AndroidRuntime(1171): Caused by: java.lang.NullPointerException 08-01 12:33:03.154: E/AndroidRuntime(1171): at android.content.ContextWrapper.getResources(ContextWrapper.java:81) 08-01 12:33:03.154: E/AndroidRuntime(1171): at android.media.MediaPlayer.create(MediaPlayer.java:824) 08-01 12:33:03.154: E/AndroidRuntime(1171): at com.hermione.woodenfish.MainActivity.<init>(MainActivity.java:23) 08-01 12:33:03.154: E/AndroidRuntime(1171): at java.lang.Class.newInstanceImpl(Native Method) 08-01 12:33:03.154: E/AndroidRuntime(1171): at java.lang.Class.newInstance(Class.java:1319) 08-01 12:33:03.154: E/AndroidRuntime(1171): at android.app.Instrumentation.newActivity(Instrumentation.java:1053) 08-01 12:33:03.154: E/AndroidRuntime(1171): at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:1974) 08-01 12:33:03.154: E/AndroidRuntime(1171): ... 11 more

你得到NullPointerException。在调试中查看MainActivity中的第23行，看看发生了什么。

错误“无法实例化活动”

2 个答案: