bug_ _java.lang.RuntimeException: Unable to start activity ComponentInfo{包名/类名}

Posted 2020-06-28 左手指月的博客

 

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:name="@+id/btn" android:layout_width="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。