Android意图按钮NullPointerException

问题描述

| 我正在尝试按一个按钮开始另一个课程。我收到了使用logcat发现的空指针异常，但我不知道为什么。

    package com.Juggle2;


import android.app.Activity;
import android.content.Intent;
import android.os.Bundle;
import android.view.View;
import android.view.View.OnClickListener;
import android.view.Window;
import android.widget.Button;

public class Juggle2 extends Activity {

    public static final String LOG_TAG = \"Juggle2\";

    @Override
    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        requestWindowFeature(Window.FEATURE_NO_TITLE);
            setContentView(R.layout.main);  


            Button StartGameButton = (Button) findViewById(R.id.StartGame);
            StartGameButton.setOnClickListener(new OnClickListener() {
                public void onClick(View v) {
                    Intent i = new Intent(Juggle2.this,StartGame.class);
                    startActivity(i);
                }
            });

我的XML清单：

<?xml version=\"1.0\" encoding=\"utf-8\"?>
<manifest xmlns:android=\"http://schemas.android.com/apk/res/android\"
      package=\"com.Juggle2\"
      android:versionCode=\"1\"
      android:versionName=\"1.0\">
    <uses-sdk android:minSdkVersion=\"10\" />

    <application android:icon=\"@drawable/icon\" android:label=\"@string/app_name\">
        <activity android:name=\".Juggle2\"
                  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=\".Panel\"></activity>
    </application>
</manifest>

这是日志

    05-27 21:12:07.749: ERROR/AndroidRuntime(6705): FATAL EXCEPTION: main
05-27 21:12:07.749: ERROR/AndroidRuntime(6705): java.lang.RuntimeException: Unable to start activity ComponentInfo{com.Juggle2/com.Juggle2.Juggle2}: java.lang.NullPointerException
05-27 21:12:07.749: ERROR/AndroidRuntime(6705):     at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:1736)
05-27 21:12:07.749: ERROR/AndroidRuntime(6705):     at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:1752)
05-27 21:12:07.749: ERROR/AndroidRuntime(6705):     at android.app.ActivityThread.access$1500(ActivityThread.java:123)
05-27 21:12:07.749: ERROR/AndroidRuntime(6705):     at android.app.ActivityThread$H.handleMessage(ActivityThread.java:993)
05-27 21:12:07.749: ERROR/AndroidRuntime(6705):     at android.os.Handler.dispatchMessage(Handler.java:99)
05-27 21:12:07.749: ERROR/AndroidRuntime(6705):     at android.os.Looper.loop(Looper.java:126)
05-27 21:12:07.749: ERROR/AndroidRuntime(6705):     at android.app.ActivityThread.main(ActivityThread.java:3997)
05-27 21:12:07.749: ERROR/AndroidRuntime(6705):     at java.lang.reflect.Method.invokeNative(Native Method)
05-27 21:12:07.749: ERROR/AndroidRuntime(6705):     at java.lang.reflect.Method.invoke(Method.java:491)
05-27 21:12:07.749: ERROR/AndroidRuntime(6705):     at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:841)
05-27 21:12:07.749: ERROR/AndroidRuntime(6705):     at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:599)
05-27 21:12:07.749: ERROR/AndroidRuntime(6705):     at dalvik.system.NativeStart.main(Native Method)
05-27 21:12:07.749: ERROR/AndroidRuntime(6705): Caused by: java.lang.NullPointerException
05-27 21:12:07.749: ERROR/AndroidRuntime(6705):     at com.Juggle2.Juggle2.onCreate(Juggle2.java:24)
05-27 21:12:07.749: ERROR/AndroidRuntime(6705):     at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1048)
05-27 21:12:07.749: ERROR/AndroidRuntime(6705):     at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:1700)
05-27 21:12:07.749: ERROR/AndroidRuntime(6705):     ... 11 more

在main.xml中： 有这个按钮

<Button
android:id=\"@+id/StartGame\"
android:layout_width=\"wrap_content\"
android:layout_height=\"wrap_content\"
android:background=\"@drawable/startgame_button\"
>

    

解决方法

        您的面板类不是活动，而是SurfaceView。因此，创建一个新的Activity类（可能称为PanelActivity），并在其onCreate（）中调用

setContentView(new Panel());

。 另外，这一行：

Intent i = new Intent().setClass(Juggle2.this,Panel.class );

应该看起来像：

Intent i = new Intent(Juggle2.this,PanelActivity.class);