android點擊返回時觸發的事件

 private void dialog(){
    	AlertDialog.Builder builder = new Builder(PPTSoftwareActivity.this);
		builder.setMessage("確認要退出麼？");
		builder.setTitle("提示");
		builder.setPositiveButton("確定", new DialogInterface.OnClickListener() {
			
			public void onClick(DialogInterface dialog, int which) {
				// TODO Auto-generated method stub
				dialog.dismiss();
				finish();
			}
		});
		builder.setNegativeButton("取消", new DialogInterface.OnClickListener() {
			
			public void onClick(DialogInterface dialog, int which) {
				// TODO Auto-generated method stub
				dialog.dismiss();
			}
		});
		builder.show();
    }

@Override
	public boolean onKeyDown(int keyCode, KeyEvent event) {
		// TODO Auto-generated method stub
		if(keyCode == KeyEvent.KEYCODE_BACK){
			dialog();
		}
		return false;
	}