在SWT程序中使用table展示数据时，如果数据过多，执行起来会比较慢，不过，我们可以借助VirtualTable来解决这一问题。
Eclipse官网中关于VirtualTable的说明见：http://www.eclipse.org/articles/Article-SWT-Virtual/Virtual-in-SWT.html
先来看一个不用VirtualTable的demo：
import org.eclipse.swt.SWT;
import org.eclipse.swt.widgets.Display;
import org.eclipse.swt.widgets.Shell;
import org.eclipse.swt.widgets.Table;
import org.eclipse.swt.widgets.TableColumn;
import org.eclipse.swt.widgets.TableItem; public class SWTTableDemo {
public static void main(String[] args) {
long start = System.currentTimeMillis();
Display display = new Display();
Shell shell = new Shell(display);
shell.setText("SWT Table Demo"); // table cell values
String[] titles = { "Column1", "Column2", "Column3", "Column4" };
int items = 20000;
String[][] cellValues = new String[items][titles.length];
for (int i = 0; i < items; i++) {
for (int j = 0; j < titles.length; j++) {
cellValues[i][j] = "cell_" + (i + 1) + "_" + (j + 1);
}
}
System.out.println("Create data cost:"+ (System.currentTimeMillis() - start)); Table table = new Table(shell, SWT.BORDER | SWT.V_SCROLL | SWT.H_SCROLL);
table.setHeaderVisible(true); // set table title
for (int i = 0; i < titles.length; i++) {
TableColumn column = new TableColumn(table, SWT.NULL);
column.setText(titles[i]);
column.pack();
} for (int loopIndex = 0; loopIndex < items; loopIndex++) {
TableItem item = new TableItem(table, SWT.NULL);
item.setText(cellValues[loopIndex]);
} table.setBounds(10, 10, 280, 350); shell.pack();
shell.open();
long end = System.currentTimeMillis();
System.out.println("All cost:" + (end - start)); while (!shell.isDisposed()) {
if (!display.readAndDispatch())
display.sleep();
}
display.dispose();
}
}
上面的代码中，虚构了20000条数据用来填充table，为了显示执行时间，代码中加入了耗时打印~~
执行以下，输出如下：
Create data cost:118
All cost:4783
先不急着评价，来看看VirtualTable的Demo：
import org.eclipse.swt.SWT;
import org.eclipse.swt.widgets.Display;
import org.eclipse.swt.widgets.Event;
import org.eclipse.swt.widgets.Listener;
import org.eclipse.swt.widgets.Shell;
import org.eclipse.swt.widgets.Table;
import org.eclipse.swt.widgets.TableColumn;
import org.eclipse.swt.widgets.TableItem; public class SWTVirtualTableDemo {
public static void main(String[] args) {
long start = System.currentTimeMillis();
Display display = new Display();
Shell shell = new Shell(display);
shell.setText("Virtual Table Demo"); //table cell values
String[] titles = { "Column1", "Column2", "Column3", "Column4" };
int items = 20000;
final String[][] cellValues = new String[items][titles.length];
for (int i = 0; i < items; i++) {
for (int j = 0; j < titles.length; j++) {
cellValues[i][j] = "cell_" + (i + 1) + "_" + (j + 1);
}
}
System.out.println("create data cost:"+(System.currentTimeMillis()-start)); Table table = new Table(shell, SWT.BORDER | SWT.V_SCROLL | SWT.H_SCROLL | SWT.VIRTUAL);
table.setHeaderVisible(true); // set table title
for (int i = 0; i < titles.length; i++) {
TableColumn column = new TableColumn(table, SWT.NULL);
column.setText(titles[i]);
column.pack();
} table.addListener(SWT.SetData, new Listener(){
public void handleEvent(Event event) {
TableItem item = (TableItem)event.item;
int index = event.index;
item.setText(cellValues [index]);
}
});
table.setItemCount(items);
table.setBounds(10, 10, 280, 350); shell.pack();
shell.open();
long end = System.currentTimeMillis();
System.out.println("All cost:" + (end - start)); while (!shell.isDisposed()) {
if (!display.readAndDispatch())
display.sleep();
}
display.dispose();
}
}
同样是虚构20000条数据用来填充table，执行以下，看看输出结果：
create data cost:118
All cost:181
一个是4783ms，一个是181ms，孰优孰劣不言自明！
使用virtual table很简单，就三个要点：
①在创建表时，加上SWT.VIRTUAL属性，eg：
//SWT.VIRTUAL
Table table = new Table(shell, SWT.BORDER | SWT.V_SCROLL | SWT.H_SCROLL | SWT.VIRTUAL);
②给表加上SWT.SetData类型的事件监听，eg：
table.addListener(SWT.SetData, new Listener(){
public void handleEvent(Event event) {
TableItem item = (TableItem)event.item;
int index = event.index;
item.setText(cellValues [index]);
}
});
③设置表中要显示的行数，eg：
table.setItemCount(items);//这里是20000
经此三个小步骤，你的表格性能将大幅得到提升