ProgressBar的可见性(Visibility of ProgressBar)

 当用户点击一个活动中的按钮时，我需要处理一些数据，所以屏幕看起来像应用程序停止2-3秒。 这不是很多，但我想给用户提供一切正常的信息，IMO最好的办法就是进度条，只有在处理数据时才能看到进度条。 
 
 我找到了ProgressBar的代码，它看起来像这样： 
 
    <ProgressBar
    android:id="@+id/loadingdata_progress"
    style="?android:attr/progressBarStyle"
    android:layout_width="50dp"
    android:layout_height="50dp"
    android:layout_alignBottom="@+id/fin2_note"
    android:layout_centerHorizontal="true"
    android:indeterminate="true"
    android:visibility="invisible" />
 
 并将其插入到我的版面中间。 
 
 而要尝试进度条的工作，我把这个代码 
 
 loadingimage= (ProgressBar) findViewById(R.id.loadingdata_progress); loadingimage.setVisibility(View.VISIBLE); 
 
 到onCreate方法，一切都很好。 然后我重新创建了代码，只有在处理数据时才显示此进度条。 
 
 点击用户调用此方法后 
 
   public void fin2_clickOnFinalization(View v)
   {    

            loadingimage= (ProgressBar) findViewById(R.id.loadingdata_progress);
    loadingimage.setVisibility(View.VISIBLE);

          // code where data is processing
            loadingimage.setVisibility(View.INVISIBLE);
       }
 
 屏幕上没有任何内容出现。 我不知道错误在哪里。 如果我通过id找到了进度条，我很奇怪我可以在onCreate方法中控制它，但在onclick方法中，它超出了我的控制范围。 

I need to process some data when the user click the button in one activity, so the screen looks like the app stops for 2-3 seconds. It isn't a lot but I want to give the user information that everything is ok and IMO the best way will be the progressbar which is visible only when data are processed. 
 
I found the code of ProgressBar and it looks like this:
 
    <ProgressBar
    android:id="@+id/loadingdata_progress"
    style="?android:attr/progressBarStyle"
    android:layout_width="50dp"
    android:layout_height="50dp"
    android:layout_alignBottom="@+id/fin2_note"
    android:layout_centerHorizontal="true"
    android:indeterminate="true"
    android:visibility="invisible" />
 
and inserted it on the middle of my layout.
 
And to try if the progressbar works, I put this code 
 
loadingimage= (ProgressBar) findViewById(R.id.loadingdata_progress); loadingimage.setVisibility(View.VISIBLE); 
 
into onCreate method and everything looks fine. Then I recreated the code to show this progressbar only if the data is processed. 
 
After click the user invoke this method 
 
   public void fin2_clickOnFinalization(View v)
   {    

            loadingimage= (ProgressBar) findViewById(R.id.loadingdata_progress);
    loadingimage.setVisibility(View.VISIBLE);

          // code where data is processing
            loadingimage.setVisibility(View.INVISIBLE);
       }
 
and nothing appear on the screen. I don't know where is the mistake. If I found the progress bar by id, It's strange for me that I can control it in onCreate method but in onclick method it's out of my control. 

原文：https://stackoverflow.com/questions/19005014