返回键直接退出应用，而非退回上一个Activity的方法。

自己总结了两种方法：

大致情况：这里有2个界面，第一个界面有个按钮，点击进入第二个界面。在第二个界面点击返回键。

1.思路：第二个Activity返回时会调用第一个Activity（上级Activity）的OnRestart（）方法，我们在OnRestart（）方法中结束本Activity。

（布局文件我就不贴了）

First.java

package a.com;
import android.app.Activity;
import android.app.AlertDialog;
import android.app.AlertDialog.Builder;
import android.content.DialogInterface;
import android.content.Intent;
import android.os.Bundle;
import android.util.Log;
import android.view.KeyEvent;
import android.view.View;
import android.view.View.OnClickListener;
import android.widget.Button;

public class First extends Activity {
	Button a;
    /** Called when the activity is first created. */
    @Override
    public void onCreate(Bundle savedInstanceState) {
    	super.onCreate(savedInstanceState);
    	setContentView(R.layout.first);
        a = (Button)findViewById(R.id.a);
		a.setOnClickListener(new OnClickListener() {
				
				public void onClick(View v) {
					// TODO Auto-generated method stub
					 Intent intent= new Intent(First.this,Next.class);
					 startActivity(intent);
					 //First.this.finish();
					// onBackPressed ();
								}
			});
    }
    	
	@Override
	public void onBackPressed() {
		// TODO Auto-generated method stub
		super.onBackPressed();
	}
	//关键代码
		@Override
	protected void onRestart() {
		
		// TODO Auto-generated method stub
		super.onRestart();
		System.out.println("OnRestart（）被调用了");
		//onBackPressed();
		// super.finish();
		First.this.finish();//结束本Activity
	}

   //提示框
    protected void dialog() { 
        AlertDialog.Builder builder = new Builder(First.this); 
        builder.setMessage("确定要退出吗?"); 
        builder.setTitle("提示"); 
        builder.setPositiveButton("确认", 
                new android.content.DialogInterface.OnClickListener() { 
                    public void onClick(DialogInterface dialog, int which) { 
                        dialog.dismiss(); 
                        First.this.finish(); 
                     //onBackPressed ();
                    } 
                }); 
        builder.setNegativeButton("取消", 
                new android.content.DialogInterface.OnClickListener() { 
                    public void onClick(DialogInterface dialog, int which) { 
                        dialog.dismiss(); 
                    } 
                }); 
        builder.create().show(); 
    } 
    
    //返回键
    @Override 
    public boolean onKeyDown(int keyCode, KeyEvent event) { 
        if (keyCode == KeyEvent.KEYCODE_BACK && event.getRepeatCount() == 0) { 
            dialog(); 
            return false; 
        } 
        return false; 
    }
}

2.思路：在点击第一个界面的按钮的同时就销毁FirstActivity



Frist.java

package a.com;
import android.app.Activity;
import android.app.AlertDialog;
import android.app.AlertDialog.Builder;
import android.content.DialogInterface;
import android.content.Intent;
import android.os.Bundle;
import android.util.Log;
import android.view.KeyEvent;
import android.view.View;
import android.view.View.OnClickListener;
import android.widget.Button;

public class First extends Activity {
	Button a;
    /** Called when the activity is first created. */
    @Override
    public void onCreate(Bundle savedInstanceState) {
    	super.onCreate(savedInstanceState);
    	setContentView(R.layout.first);
        a = (Button)findViewById(R.id.a);
		a.setOnClickListener(new OnClickListener() {
				
				public void onClick(View v) {
					// TODO Auto-generated method stub
					 Intent intent= new Intent(First.this,Next.class);
					 startActivity(intent);
					 First.this.finish();关键点，结束了本Activity。
					// onBackPressed ();也可以结束Activity
							                            }
			});
    }
    	
	@Override
	public void onBackPressed() {
		// TODO Auto-generated method stub
		super.onBackPressed();
	}
	
		@Override
	protected void onRestart() {
		
		// TODO Auto-generated method stub
		super.onRestart();
		System.out.println("OnRestart（）被调用了");
		//onBackPressed();
		// super.finish();
		First.this.finish();
	}

   //提示框
    protected void dialog() { 
        AlertDialog.Builder builder = new Builder(First.this); 
        builder.setMessage("确定要退出吗?"); 
        builder.setTitle("提示"); 
        builder.setPositiveButton("确认", 
                new android.content.DialogInterface.OnClickListener() { 
                    public void onClick(DialogInterface dialog, int which) { 
                        dialog.dismiss(); 
                        First.this.finish(); 
                     //onBackPressed ();
                    } 
                }); 
        builder.setNegativeButton("取消", 
                new android.content.DialogInterface.OnClickListener() { 
                    public void onClick(DialogInterface dialog, int which) { 
                        dialog.dismiss(); 
                    } 
                }); 
        builder.create().show(); 
    } 
    
    //返回键
    @Override 
    public boolean onKeyDown(int keyCode, KeyEvent event) { 
        if (keyCode == KeyEvent.KEYCODE_BACK && event.getRepeatCount() == 0) { 
            dialog(); 
            return false; 
        } 
        return false; 
    }
}

Next.java

package a.com;
import android.app.Activity;
import android.app.AlertDialog;
import android.app.AlertDialog.Builder;
import android.content.DialogInterface;
import android.content.Intent;
import android.os.Bundle;
import android.view.KeyEvent;
import android.view.View;
import android.view.View.OnClickListener;
import android.widget.Button;

public class Next extends Activity {
    /** Called when the activity is first created. */
    @Override
    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.next);
    
    }
    //提示框
    protected void dialog() { 
        AlertDialog.Builder builder = new Builder(Next.this); 
        builder.setMessage("确定要退出吗?"); 
        builder.setTitle("提示"); 
        builder.setPositiveButton("确认", 
                new android.content.DialogInterface.OnClickListener() { 
                    public void onClick(DialogInterface dialog, int which) { 
                        dialog.dismiss(); 
                        First.this.finish(); //结束本Activity
                        onBackPressed ();//也可以结束Activity，详情见官网。
                    } 
                }); 
        builder.setNegativeButton("取消", 
                new android.content.DialogInterface.OnClickListener() { 
                    public void onClick(DialogInterface dialog, int which) { 
                        dialog.dismiss(); 
                    } 
                }); 
        builder.create().show(); 
    } 
    //返回键
    @Override 
    public boolean onKeyDown(int keyCode, KeyEvent event) { 
        if (keyCode == KeyEvent.KEYCODE_BACK && event.getRepeatCount() == 0) { 
            dialog(); 
            return false; 
        } 
        return false; 
    }
}

Next.java

package a.com;
import android.app.Activity;
import android.app.AlertDialog;
import android.app.AlertDialog.Builder;
import android.content.DialogInterface;
import android.content.Intent;
import android.os.Bundle;
import android.view.KeyEvent;
import android.view.View;
import android.view.View.OnClickListener;
import android.widget.Button;

public class Next extends Activity {
    /** Called when the activity is first created. */
    @Override
    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.next);
    
    }
    //提示框
    protected void dialog() { 
        AlertDialog.Builder builder = new Builder(Next.this); 
        builder.setMessage("确定要退出吗?"); 
        builder.setTitle("提示"); 
        builder.setPositiveButton("确认", 
                new android.content.DialogInterface.OnClickListener() { 
                    public void onClick(DialogInterface dialog, int which) { 
                        dialog.dismiss(); 
                       // First.this.finish(); 
                          onBackPressed ();
                    } 
                }); 
        builder.setNegativeButton("取消", 
                new android.content.DialogInterface.OnClickListener() { 
                    public void onClick(DialogInterface dialog, int which) { 
                        dialog.dismiss(); 
                    } 
                }); 
        builder.create().show(); 
    } 
    //返回键
    @Override 
    public boolean onKeyDown(int keyCode, KeyEvent event) { 
        if (keyCode == KeyEvent.KEYCODE_BACK && event.getRepeatCount() == 0) { 
            dialog(); 
            return false; 
        } 
        return false; 
    }
}