java JScrollPane 设置滚动位置
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JScrollPane Set Scroll Position
提问by aditya parikh
I have following code snippet
我有以下代码片段
query_area = new JTextArea("");
query_scroll_pane = new JScrollPane(query_area);
query_scroll_pane.setSize(1000,80);
query_scroll_pane.setLocation(10,10);
query_panel.add(query_scroll_pane);
which adds my textarea to scrollpane. Now in a method i dynamically set text for the textarea as
它将我的 textarea 添加到滚动窗格。现在在一种方法中，我将 textarea 的文本动态设置为
sf.query_area.setText("Query "+(sf.query_counter)+sf.query_store[sf.query_counter]);
System.out.println("Position: "+sf.query_scroll_pane.getHorizontalScrollBar().getValue());
Now my query is when longer text is displayed, scrollbars appear but system.out.println prints position of scrollbar as 0 and not some increased value.
现在我的查询是当显示更长的文本时，滚动条出现但 system.out.println 将滚动条的位置打印为 0 而不是一些增加的值。
Why so ??
为什么这样 ？？
回答by MadProgrammer
The only reason I can think of is because the view port position hasn't changed.
我能想到的唯一原因是视口位置没有改变。
The first thing that comes to mind, is the view port may not have yet reacted to a change in position from the text begin set, so dumping the result immediately after you've set the text is reflecting the current state of the scroll bar (which has not yet begin updated)
首先想到的是，视口可能尚未对文本开始设置的位置变化做出反应，因此在设置文本后立即转储结果反映了滚动条的当前状态（尚未开始更新）
You could try
你可以试试
SwingUtilities.invokeLater(new Runnable() {
public void run() {
System.out.println("Position: "+sf.query_scroll_pane.getHorizontalScrollBar().getValue());
}
});
instead and see if that prints out a more up-to-date value
相反，看看它是否打印出更新的值
Alternativly, you could add a AdjustmentListenerto the scroll bar, which will notify when changes occur JScrollBar#addAdjustmentListener
或者，您可以AdjustmentListener向滚动条添加一个，它会在发生更改时通知JScrollBar#addAdjustmentListener
回答by mKorbel
Now my query is when longer text is displayed, scrollbars appear but system.out.println prints position of scrollbar as 0 and not some increased value.
现在我的查询是当显示更长的文本时，滚动条出现但 system.out.println 将滚动条的位置打印为 0 而不是一些增加的值。
use
利用
query_area = new JTextArea();
DefaultCaret caret = (DefaultCaret) query_area.getCaret();
caret.setUpdatePolicy(DefaultCaret.ALWAYS_UPDATE);
