Android Back返回键 退出

    @Override
    public boolean onKeyDown(int keyCode, KeyEvent event) {
        // TODO Auto-generated method stub
        if (keyCode == KeyEvent.KEYCODE_BACK) {
            new AlertDialog.Builder(this).setTitle("提示").setMessage("确定退出吗？")
                .setPositiveButton("确定", new DialogInterface.OnClickListener() {

                    @Override
                    public void onClick(DialogInterface dialog, int which) {
                        // TODO Auto-generated method stub
                        finish();
                    }
                
                })
                .setNegativeButton("取消", new DialogInterface.OnClickListener() {

                    @Override
                    public void onClick(DialogInterface dialog, int which) {
                        // TODO Auto-generated method stub
                        
                    }
                    
                }).show();
            return true;
        }else{
            return super.onKeyDown(keyCode, event);
        }
    }
    
    @Override
    protected void onDestroy() {
        // TODO Auto-generated method stub
        super.onDestroy();
        System.exit(0);
        // 或者下面这种方式  
//        android.os.Process.killProcess(android.os.Process.myPid());
    }