android按返回键，弹出退出提示对话框，并退出应用程序。

@Override
public boolean onKeyDown(int keyCode, KeyEvent event) {
// TODO Auto-generated method stub
switch (keyCode) {
case KeyEvent.KEYCODE_BACK:
AlertDialog.Builder build=new AlertDialog.Builder(this);
build.setTitle("注意")
.setMessage("确定要退出吗？")
.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();
break;

default:
break;
}
return false;
//return super.onKeyDown(keyCode, event);