与按钮相关的问题：试图在空对象引用上调用虚拟方法

Question

我在Android中面临这个问题。01-30 20:32:57.415 242 27-24227/edu.gatech.seclass.vcipher e/androidruntime：致命异常：main process：edu.gatech.seclass.vcipher,pid：24227 java.lang.runtimeexception：无法启动活动ComponentInfo{edu.gatech.seclass.vcipher/edu.gatech.seclass.vcipheractivity}:java.lang.nullpointerexception：试图在Android.app.activity的空对象引用上调用虚拟方法'void在Android.app.activitythread.handlelaunchactivity（activitythread.java:2946)在Android.app.activitythread.java:3046)在Android.app.activitythread.-Wrap11（未知源码：0）在Android.app.activitythread.-Wrap11（未知源码：0）在Android.app.activitythread.$h.handleMessage（activitythread.java:1688)在Android.os.handler.dispatchMessage（handler.java:105)在）在com.android.internal.os.zygote$methodandargscaller.run(zygote.java:240)(com.android.internal.os.zygoteinit.main(zygoteinit.java:767)引起的原因是：java.lang.nullpointerException：试图在endu.gatech.seclass.vcipher.vcipherActivity.onCreate(vcipherActivity.java:48)和android.app.activity.performCreate(activity.java:6998)和android.app.instrumentation.callactivityonCreate（在Android.app.activitythread.performLaunchActivity（activitythread.java:2899)在Android.app.activitythread.handleLaunchActivity（activitythread.java:3046) 在Android.app.activitythread.-Wrap11（未知来源：0） 在Android.app.activitythread$h.handleMessage(activitythread.java:1688) 在Android.os.handler.DispatchMessage(Handler.java:105) 在Android.os.looper.loop(looper.java:164) 在Android.app.activitythread.main（activitythread.java:6809) 在java.lang.reflect.Method.invoke（本机方法） 在com.android.internal.os.zygote$methodandargscaller.run(zygote.java:240) 在com.android.internal.os.zygoteinit.main(zygoteinit.java:767) -------------------------------------------------------------------------------------------------------------------但是我的按钮引用不是空的，但我仍然得到这个问题。

Please help me in resolving this.I am stucked in my android development due to this issue. Not able to resolve it.Help is very much appreciated.

Thanks

Answer 1

因为xml上的id是Android:id=“@+id/button”而不是BTN。
您必须更改

final android.widget.Button button1 = (Button) findViewById(R.id.btn);

到

final android.widget.Button button1 = (Button) findViewById(R.id.button);