bug_ _java.lang.RuntimeException: Unable to start activity ComponentInfo{包名/类名}
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写这篇博文,我顶着很大的压力,贴出来会引来网友的一片鄙视,不贴我又觉得对不起android SDK研发团队。
本着对全世界Android无产者负责的态度,今天不得不指出Android编译时隐藏的很深的一个Bug.
以下为我的TestActivity类:
public class TestActivity extends Activity {
private static final String TAG = "TestActivity";
private Button button;
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.main);
button = (Button)findViewById(R.id.btn);
button.setOnClickListener(new OnClickListener() {
@Override
public void onClick(View v) {
Log.d(TAG, "onClick. ");
}
});
}
}
该类在AndroidMenifest.xml中是这样设置的:
android:label="@string/app_name">
布局文件为res/layout/main.xml:
android:orientation="vertical" android:layout_width="fill_parent"
android:layout_height="fill_parent">
android:layout_height="wrap_content" android:text="start"/>
很简单吧,当我编译时,也完全正常.但是当在Eclipse中点击运行时,抛出如下异常:
java.lang.RuntimeException: Unable to start activity ComponentInfo{com.orange.test/com.orange.test.TestActivity}: java.lang.NullPointerException
at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2663)
at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2679)
at android.app.ActivityThread.access$2300(ActivityThread.java:125)
at android.app.ActivityThread$H.handleMessage(ActivityThread.java:2033)
at android.os.Handler.dispatchMessage(Handler.java:99)
at android.os.Looper.loop(Looper.java:123)
at android.app.ActivityThread.main(ActivityThread.java:4627)
at java.lang.reflect.Method.invokeNative(Native Method)
at java.lang.reflect.Method.invoke(Method.java:521)
at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:868)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:626)
at dalvik.system.NativeStart.main(Native Method)
Caused by: java.lang.NullPointerException
at com.orange.test.TestActivity.onCreate(TestActivity.java:24)
at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1047)
at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2627)
... 11 more
很是匪夷所思,这么一个简单的问题,button=(Button)findViewById(R.id.btn);
button对象值竟然为null,我又去查看gen/目录下的com.orange.test.R.java文件:内容如下
public final class R {
public static final class attr {
}
public static final class drawable {
public static final int icon=0x7f020000;
}
public static final class id {
public static final int btn=0x7f050000;
}
public static final class layout {
public static final int main=0x7f030000;
}
public static final class string {
public static final int app_name=0x7f040001;
public static final int hello=0x7f040000;
}
}
一切都正常啊,R.id.btn这不是正常地生成了吗!!!!,找来大拿,不顶用,同样没有发现。
最后无意识地发现,android:name="@+id/btn" 应该是android:id="@+id/btn".
悲剧的是,Android编译时,竟然没有发现这里的错误。
最为可气的是,竟然还在R.java文件中生成了
public static final class id {
public static final int btn=0x7f050000;
}
这得害了多少无辜的程序员。
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