SWT table性能改善 -- 使用VirtualTable

在SWT程序中使用table展現數據時，若是數據過多，執行起來會比較慢，不過，咱們能夠藉助VirtualTable來解決這一問題。

Eclipse官網中關於VirtualTable的說明見：http://www.eclipse.org/articles/Article-SWT-Virtual/Virtual-in-SWT.html

 

先來看一個不用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();
    }
}

上面的代碼中，虛構了20000條數據用來填充table，爲了顯示執行時間，代碼中加入了耗時打印~~

執行如下，輸出以下：

Create data cost:118
All cost:4783

先不急着評價，來看看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();
    }
}

一樣是虛構20000條數據用來填充table，執行如下，看看輸出結果：

create data cost:118
All cost:181

一個是4783ms，一個是181ms，孰優孰劣不言自明！

 

使用virtual table很簡單，就三個要點：

①在建立表時，加上SWT.VIRTUAL屬性，eg：

//SWT.VIRTUAL
Table table = new Table(shell, SWT.BORDER | SWT.V_SCROLL | SWT.H_SCROLL | SWT.VIRTUAL);

②給表加上SWT.SetData類型的事件監聽，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設置表中要顯示的行數，eg：

table.setItemCount(items);//這裏是20000

 

經此三個小步驟，你的表格性能將大幅獲得提高