从一个活动（布局）跳转到另一个活动的问题

Question

你好只是头痛。无法找到问题。所有按钮都正常工作，并从一个活动正确跳转到另一个活动，但“按钮关于”无法正常工作。它必须跳到“关于活动”...请检查代码问题...“关于按钮”有问题有评论，并在最后...谢谢和问候

有关于按钮的活动

package com.example.routetracker;



import android.media.MediaPlayer;
import android.os.Bundle;
import android.app.Activity;
import android.content.Intent;
import android.view.View;
import android.view.View.OnClickListener;
import android.widget.Button;

public class Select_destination extends Activity implements OnClickListener{
Button close,main,about,texila,aslam_market,royal_son,comsat;
MediaPlayer mPlayer;

@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_select_destination);

    mPlayer=MediaPlayer.create(this, R.raw.selectdestination);


            mPlayer.start();
            texila=(Button)findViewById(R.id.btn_texila);
            texila.setOnClickListener(this);
            aslam_market=(Button)findViewById(R.id.btn_aslam_market);
            aslam_market.setOnClickListener(this);
            royal_son=(Button)findViewById(R.id.btn_royal_son);
            royal_son.setOnClickListener(this);
            comsat=(Button)findViewById(R.id.btn_comsat_wah);
            comsat.setOnClickListener(this);
            main=(Button)findViewById(R.id.btn_main);
            main.setOnClickListener(this);
            about=(Button)findViewById(R.id.btn_about);
            about.setOnClickListener(this);
            close=(Button)findViewById(R.id.btn_close);
            close.setOnClickListener(this);
}


@Override
public void onClick(View v) {
    switch(v.getId()){
    case R.id.btn_texila:
        mPlayer.stop();

        Intent i=new Intent(Select_destination.this,Start_tracking.class);
        i.putExtra("place", "1");
        startActivity(i);
        break;
    case R.id.btn_aslam_market:
        mPlayer.stop();
        Intent j=new Intent(Select_destination.this,Start_tracking.class);
        j.putExtra("place", "2");
        startActivity(j);
        break;
    case R.id.btn_royal_son:
        mPlayer.stop();
        Intent k=new Intent(Select_destination.this,Start_tracking.class);
        k.putExtra("place", "3");
        startActivity(k);
        break;
    case R.id.btn_comsat_wah:
        mPlayer.stop();
        Intent l=new Intent(Select_destination.this,Start_tracking.class);
        l.putExtra("place", "4");
        startActivity(l);
        break;

    case R.id.btn_main:
        mPlayer.stop();
        Intent o=new Intent(Select_destination.this,MainActivity.class);
        startActivity(o);
        break;

    case R.id.btn_about:  // for this button i have problem
        mPlayer.stop();
        Intent e=new Intent(Select_destination.this,About.class);
        startActivity(e);
        break;



    case R.id.btn_close:
        mPlayer.stop();
        System.exit(1);
    }

}


}

关于活动代码

package com.example.routetracker;

import android.os.Bundle;
import android.app.Activity;
import android.content.Intent;
import android.view.View;
import android.view.View.OnClickListener;
import android.widget.Button;


public class About extends Activity implements OnClickListener{

Button close,main;

@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_about);

    main=(Button)findViewById(R.id.btn_main);
    main.setOnClickListener(this);

    close=(Button)findViewById(R.id.btn_close);
    close.setOnClickListener(this);
}

@Override
public void onClick(View v) {
    switch(v.getId()){
    case R.id.btn_main:
        Intent o=new Intent(About.this,MainActivity.class);
        startActivity(o);
        break;

    case R.id.btn_close:
        System.exit(1);
        break;


    }


}

}

关于按钮的XML代码

<Button
    android:id="@+id/btn_about"
    android:layout_width="97dp"
    android:layout_height="90dp"
    android:layout_alignBaseline="@+id/btn_main"
    android:layout_alignBottom="@+id/btn_main"
    android:layout_toRightOf="@+id/btn_main"
    android:text="About" />