当运行我的基本应用程序时，我收到以下错误消息。该应用程序由一个名为button1的按钮和一个名为topLeft的textView组成。
这是什么意思？为什么我的代码在尝试引用R.java文件时出现问题？
感谢您的提前帮助。
07-01 15:33:02.754: D/AndroidRuntime(2334): Shutting down VM 07-01 15:33:02.754: W/dalvikvm(2334): threadid=1: thread exiting with
uncaught exception (group=0x40a13300) 07-01 15:33:02.984:
E/AndroidRuntime(2334): FATAL EXCEPTION: main 07-01 15:33:02.984:
E/AndroidRuntime(2334): java.lang.RuntimeException: Unable to instantiate activity
ComponentInfo{com.example.myfirstapp/com.example.myfirstapp.MainActivity}:
java.lang.NullPointerException 07-01 15:33:02.984:
E/AndroidRuntime(2334): at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:1983)
07-01 15:33:02.984: E/AndroidRuntime(2334): at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2084)
07-01 15:33:02.984: E/AndroidRuntime(2334): at android.app.ActivityThread.access$600(ActivityThread.java:130) 07-01
15:33:02.984: E/AndroidRuntime(2334): at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1195)
07-01 15:33:02.984: E/AndroidRuntime(2334): at android.os.Handler.dispatchMessage(Handler.java:99) 07-01
15:33:02.984: E/AndroidRuntime(2334): at android.os.Looper.loop(Looper.java:137) 07-01 15:33:02.984:
E/AndroidRuntime(2334): at android.app.ActivityThread.main(ActivityThread.java:4745) 07-01
15:33:02.984: E/AndroidRuntime(2334): at java.lang.reflect.Method.invokeNative(Native Method) 07-01
15:33:02.984: E/AndroidRuntime(2334): at java.lang.reflect.Method.invoke(Method.java:511) 07-01 15:33:02.984:
E/AndroidRuntime(2334): at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:786)
07-01 15:33:02.984: E/AndroidRuntime(2334): at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:553) 07-01
15:33:02.984: E/AndroidRuntime(2334): at dalvik.system.NativeStart.main(Native Method) 07-01 15:33:02.984:
E/AndroidRuntime(2334): Caused by: java.lang.NullPointerException
07-01 15:33:02.984: E/AndroidRuntime(2334): at android.app.Activity.findViewById(Activity.java:1825) 07-01
15:33:02.984: E/AndroidRuntime(2334): at com.example.myfirstapp.MainActivity.<init>(MainActivity.java:28) 07-01
15:33:02.984: E/AndroidRuntime(2334): at java.lang.Class.newInstanceImpl(Native Method) 07-01 15:33:02.984:
E/AndroidRuntime(2334): at java.lang.Class.newInstance(Class.java:1319) 07-01 15:33:02.984:
E/AndroidRuntime(2334): at android.app.Instrumentation.newActivity(Instrumentation.java:1053)
07-01 15:33:02.984: E/AndroidRuntime(2334): at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:1974)
07-01 15:33:02.984: E/AndroidRuntime(2334): ... 11 more
当尝试使用findViewById时，会出现这个错误，指向第28行。
程序如下所示：
package com.example.myfirstapp;
import android.app.Activity;
import android.os.Bundle;
import android.view.Menu;
import android.view.View;
import android.view.View.OnClickListener;
import android.widget.Button;
import android.widget.TextView;
public class MainActivity extends Activity implements OnClickListener{
int a = 0;
@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;
}
Button button1 = (Button) findViewById(R.id.button1);
TextView topLeft = (TextView) findViewById(R.id.textView2);
// button1.setOnClickListener( this );
public void onClick(View v) {
// TODO Auto-generated method stub
}
}
这是什么意思？为什么我的代码在尝试引用R.java文件时出现问题？
R.java does have
public static final class id {
public static final int button1=0x7f080001;
public static final int menu_settings=0x7f080003;
public static final int textView1=0x7f080000;
public static final int textView2=0x7f080002;
感谢您的提前帮助。