Android id无法解析或不是字段

这是我的main.xml文件

package com.commonsware.android.layouts;

import android.app.Activity;
import android.os.Bundle;
import android.view.View;
import android.widget.Button;
import java.util.Date;
public class NowRedux1 extends Activity implements View.OnClickListener  {
    Button btn;
    /** Called when the activity is first created. */
    @Override
    public void onCreate(Bundle icicle) {
        super.onCreate(icicle);
        setContentView(R.layout.main);
        **btn=(Button)findViewById(R.id.button);///Error**
        btn.setOnClickListener(this);
        updateTime();
    }
    public void onClick(View view){
        updateTime();

    }
    private void updateTime(){
        btn.setText(new Date().toString());
    }


}

---

请发送问候

从您的格式设置中可以看出，您的

main.xml

不包含任何按钮。您必须添加一个带有id按钮的按钮

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:orientation="vertical"
    android:layout_width="fill_parent"
    android:layout_height="fill_parent"
    >
<TextView  
    android:layout_width="fill_parent" 
    android:layout_height="wrap_content" 
    android:text="@string/hello"
    />
</LinearLayout>

package com.commonsware.android.layouts;

public final class R {
    public static final class attr {
    }
    public static final class drawable {
        public static final int icon=0x7f020000;
    }
    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;
    }
}