2.3 GridLayout
GridLayout可能是最常用的、功能最強大的標準佈局類了,當然它也最複雜。GridLayout把容器裏的組件擺放在一個格子裏,它有許多可設置的域,並且同RowLayout類似,組件可以有相應的佈局數據,稱作GridData。GridLayout的強大在於它可以通過GridData來設置每一個控件。
2.3.1 GridLayout的可設置域
numColumns
numColumns 域是GridLayout的最重要的域,並且通常是第一個需要設置的域。組件從左到右擺放在列裏,當numColumns + 1個組件添加到容器中時,將創建一個新行。默認只有一列。以下代碼創建了由GridLayout管理的含有5個具有不同寬度的按鈕的Shell,隨後的列表顯示了當numColumns設爲1,2或3時的效果。
Display display = new Display();
Shell shell = new Shell(display);
GridLayout gridLayout = new GridLayout();
gridLayout.numColumns = 3;
shell.setLayout(gridLayout);
new Button(shell, SWT.PUSH).setText("B1");
new Button(shell, SWT.PUSH).setText("Wide Button 2");
new Button(shell, SWT.PUSH).setText("Button 3");
new Button(shell, SWT.PUSH).setText("B4");
new Button(shell, SWT.PUSH).setText("Button 5");
shell.pack();
shell.open();
while (!shell.isDisposed()) {
if (!display.readAndDispatch()) display.sleep();
}
numColumns = 1 |
numColumns = 2 |
numColumns = 3 |
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makeColumnsEqualWidth
makeColumnsEqualWidth域強制各列具有相同的寬度。默認爲false。把上面的例子改爲含有3個等寬的列,效果如下圖所示(注意組件在列中左對齊,原因見後面介紹):
MarginWidth, MarginHeight, HorizontalSpacing, 以及 VerticalSpacing
GridLayout邊距和間距域與RowLayout的類似,不同的是左邊距和右邊距統一成marginWidth,上邊距和下邊距統一成marginHeight。同樣可以分別設置horizontalSpacing和verticalSpacing(RowLayout中的間距根據它的type類型設置水平間距或者垂直間距)。
2.3.2 GridData對象的域
GridData是GridLayout對應的佈局數據,可以通過setLayoutData設置組件的佈局數據。例如,可以採用如下代碼設置按鈕的GridData:
Button button1 = new Button(shell, SWT.PUSH);
button1.setText("B1");
button1.setLayoutData(new GridData());
以上代碼創建了一個含有默認值的GridData對象,其效果和沒有設置佈局數據是一樣的。有兩種方式可以創建含有指定域值的GridData對象。第一種方式就是直接設置各個域值,例如:
GridData gridData = new GridData();
gridData.horizontalAlignment = GridData.FILL;
gridData.grabExcessHorizontalSpace = true;
button1.setLayoutData(gridData);
第二種方式是通過利用便利的API來設置GridData的風格位:
button1.setLayoutData(new GridData(GridData.HORIZONTAL_ALIGN_FILL | GridData.GRAB_HORIZONTAL));
實際上,爲了更方便還提供了一些風格位的組合,例如:
button1.setLayoutData(new GridData(GridData.FILL_HORIZONTAL));
注意FILL_ 風格同時設置對齊方式和佔位方式。GridData的風格位只對布爾值和枚舉值有效,數字域需要直接設置。
(使用Swing者注意) 最後使用GridData時需要主要的是:不要重複使用GridData 對象。每一個由GridLayout容器管理的組件必須有單獨的GridData對象。如果組件的佈局數據爲空,則SWT會自動創建一個單獨的GridData對象。
HorizontalAlignment 及 VerticalAlignment
alignment域指定組件在格子裏按照水平或者垂直方式擺放。可以設置以下值:
· BEGINNING
· CENTER
· END
· FILL
默認horizontalAlignment設爲BEGINNING (左對齊),verticalAlignment設爲CENTER。
參考前面的五個按鈕的例子,設置三列,並對Button 5設置不同的horizontalAlignment,如圖:
horizontalAlignment = GridData.BEGINNING (默認) |
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horizontalAlignment = GridData.CENTER |
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horizontalAlignment = GridData.END |
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horizontalAlignment = GridData.FILL |
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HorizontalIndent
horizontalIndent域可以使組件向右移動指定的像素值。只有當horizontalAlignment設爲BEGINNING時有效。不能通過風格位設置縮進,以下代碼演示了把Button 5縮進4個像素:
GridData gridData = new GridData();
gridData.horizontalIndent = 4;
button5.setLayoutData(gridData);
HorizontalSpan 及 VerticalSpan
span域可以使控件跨越幾個格子,常常與FILL風格一起使用。以下代碼把Button 5擴展到了兩個格子:
GridData gridData = new GridData();
gridData.horizontalAlignment = GridData.FILL;
gridData.horizontalSpan = 2;
button5.setLayoutData(gridData);
如果要把Button 2擴展到兩個格子,可以這樣寫:
GridData gridData = new GridData();
gridData.horizontalAlignment = GridData.FILL;
gridData.horizontalSpan = 2;
button2.setLayoutData(gridData);
還可以把Button 3垂直擴展兩個格子:
GridData gridData = new GridData();
gridData.verticalAlignment = GridData.FILL;
gridData.verticalSpan = 2;
button3.setLayoutData(gridData);
GrabExcessHorizontalSpace 及 GrabExcessVerticalSpace
grabExcessHorizontalSpace和grabExcessVerticalSpace主要用在象Text, List及Canvas這樣的重量級組件上,當它們所在的容器增大時,可以使它們自動增大。例如如果設置一個Text組件可以橫向擴展,那麼當用戶調整Shell的寬度時,Text組件會自動擴展填滿新的橫向空間,而同一行上的其他組件保持寬度不變。當然,當Shell變小時,設置了此屬性的組件也是首先收縮的。在可以調整容器大小的環境中,很容易的就能想到設置grabExcessSpace域。作爲例子,我們仍然採用前面Button 3垂直擴展兩個單元格的例子,如下:
如果我們調整窗口的大小,那麼只有窗口變大了:
現在設置Button 3可以橫向和縱向擴展,B1和B4僅縱向填充(不擴展),重新調整之後,如圖:
這一次,Button 3在兩個方向上變化了,B4只在縱向上變化,其它保持不變。這是由於設置了Button 3在縱向上擴展,最後一行變高了的結果。注意B1沒有變化,儘管對它設置了縱向填充,因爲它所在的行沒有變化。並且Button 3還設置了橫向擴展和填充,它所在的列變寬了,所以它也變寬了。以下是代碼:
Button button1 = new Button(shell, SWT.PUSH);
button1.setText("B1");
GridData gridData = new GridData();
gridData.verticalAlignment = GridData.FILL;
button1.setLayoutData(gridData);
new Button(shell, SWT.PUSH).setText("Wide Button 2");
Button button3 = new Button(shell, SWT.PUSH);
button3.setText("Button 3");
gridData = new GridData();
gridData.verticalAlignment = GridData.FILL;
gridData.verticalSpan = 2;
gridData.grabExcessVerticalSpace = true;
gridData.horizontalAlignment = GridData.FILL;
gridData.grabExcessHorizontalSpace = true;
button3.setLayoutData(gridData);
Button button4 = new Button(shell, SWT.PUSH);
button4.setText("B4");
gridData = new GridData();
gridData.verticalAlignment = GridData.FILL;
button4.setLayoutData(gridData);
new Button(shell, SWT.PUSH).setText("Button 5");
在典型的應用程序窗口中,通常會設置至少一個組件可以擴展。如果有多於一個的組件可以擴展,那麼它們平均分配擴展的空間,如圖所示:
最後需要注意的是,如果一個組件可以橫向擴展,並且它的父容器變寬了,那麼組件所在的整列都變寬了。同樣如果組件可以縱向擴展,並且其父容器變高了,那麼組件所在的整行都變高了。這樣如果相應的行或列裏有其它的組件設置了填充(fill)屬性,那麼這些組件也會被拉伸。具有左對齊、居中對齊、右對齊的組件不會被拉伸,它們仍然在所在的行或列裏左對齊、居中對齊或右對齊。
WidthHint 及 HeightHint
widthHint和heightHint域指示了希望組件可以具有的寬度和高度,前提是不與GridLayout其他要求約束矛盾。參見前面五個按鈕、三列的例子,假設要設置Button 5寬70像素、高40像素,代碼如下:
GridData gridData = new GridData();
gridData.widthHint = 70;
gridData.heightHint = 40;
button5.setLayoutData(gridData);
Button 5自然尺寸如左圖所示,右圖是70像素寬、 40像素高的圖示:
注意,如果Button 5的horizontalAlignment設置爲FILL,那麼GridLayout不能滿足其寬爲70像素的請求。
最後一點,在一個平臺上表現好的設置,在另一個平臺上可能會有差別。由於不同平臺之間的字體大小和組件的自然大小不一樣,因此硬編碼像素值不是佈局窗體的最好方法。因而,除非萬不得已,儘量少用size hint。
2.3.3 一個複雜的GridLayout例子
前面列舉的GridLayout例子都比較簡單,只是用來說明各個域的效果如何。接下來,舉一個很複雜的例子,把各個域的效果綜合在一起。我們先手工畫下要創建的窗體的草圖,幫助我們決定需要多少列,那些組件需要擴展:
然後根據上面的草圖開始編碼,如下所示。注意,我們添加了一些邏輯來使例子更生動一些,比如,Browse…打開一個FileDialog對話框,用來讀入一個圖像文件,Canvas在渲染監聽器中顯示圖像,Delete刪除圖像,Enter打印當前信息。示例代碼放在單一的main方法裏,目的是使我們注重於佈局代碼,而不是程序風格上。
import org.eclipse.swt.*;
import org.eclipse.swt.widgets.*;
import org.eclipse.swt.layout.*;
import org.eclipse.swt.events.*;
import org.eclipse.swt.graphics.*;
public class ComplexGridLayoutExample {
static Display display;
static Shell shell;
static Text dogName;
static Combo dogBreed;
static Canvas dogPhoto;
static Image dogImage;
static List categories;
static Text ownerName;
static Text ownerPhone;
public static void main(String[] args) {
display = new Display();
shell = new Shell(display);
shell.setText("Dog Show Entry");
GridLayout gridLayout = new GridLayout();
gridLayout.numColumns = 3;
shell.setLayout(gridLayout);
new Label(shell, SWT.NONE).setText("Dog's Name:");
dogName = new Text(shell, SWT.SINGLE | SWT.BORDER);
GridData gridData = new GridData(GridData.HORIZONTAL_ALIGN_FILL);
gridData.horizontalSpan = 2;
dogName.setLayoutData(gridData);
new Label(shell, SWT.NONE).setText("Breed:");
dogBreed = new Combo(shell, SWT.NONE);
dogBreed.setItems(new String [] {"Collie", "Pitbull", "Poodle", "Scottie"});
dogBreed.setLayoutData(new GridData(GridData.HORIZONTAL_ALIGN_FILL));
Label label = new Label(shell, SWT.NONE);
label.setText("Categories");
label.setLayoutData(new GridData(GridData.HORIZONTAL_ALIGN_CENTER));
new Label(shell, SWT.NONE).setText("Photo:");
dogPhoto = new Canvas(shell, SWT.BORDER);
gridData = new GridData(GridData.FILL_BOTH);
gridData.widthHint = 80;
gridData.heightHint = 80;
gridData.verticalSpan = 3;
dogPhoto.setLayoutData(gridData);
dogPhoto.addPaintListener(new PaintListener() {
public void paintControl(final PaintEvent event) {
if (dogImage != null) {
event.gc.drawImage(dogImage, 0, 0);
}
}
});
categories = new List(shell, SWT.MULTI | SWT.BORDER | SWT.V_SCROLL);
categories.setItems(new String [] {
"Best of Breed", "Prettiest Female", "Handsomest Male",
"Best Dressed", "Fluffiest Ears", "Most Colors",
"Best Performer", "Loudest Bark", "Best Behaved",
"Prettiest Eyes", "Most Hair", "Longest Tail",
"Cutest Trick"});
gridData = new GridData(GridData.HORIZONTAL_ALIGN_FILL | GridData.VERTICAL_ALIGN_FILL);
gridData.verticalSpan = 4;
int listHeight = categories.getItemHeight() * 12;
Rectangle trim = categories.computeTrim(0, 0, 0, listHeight);
gridData.heightHint = trim.height;
categories.setLayoutData(gridData);
Button browse = new Button(shell, SWT.PUSH);
browse.setText("Browse...");
gridData = new GridData(GridData.HORIZONTAL_ALIGN_FILL);
gridData.horizontalIndent = 5;
browse.setLayoutData(gridData);
browse.addSelectionListener(new SelectionAdapter() {
public void widgetSelected(SelectionEvent event) {
String fileName = new FileDialog(shell).open();
if (fileName != null) {
dogImage = new Image(display, fileName);
}
}
});
Button delete = new Button(shell, SWT.PUSH);
delete.setText("Delete");
gridData = new GridData(GridData.HORIZONTAL_ALIGN_FILL | GridData.VERTICAL_ALIGN_BEGINNING);
gridData.horizontalIndent = 5;
delete.setLayoutData(gridData);
delete.addSelectionListener(new SelectionAdapter() {
public void widgetSelected(SelectionEvent event) {
if (dogImage != null) {
dogImage.dispose();
dogImage = null;
dogPhoto.redraw();
}
}
});
Group ownerInfo = new Group(shell, SWT.NONE);
ownerInfo.setText("Owner Info");
gridLayout = new GridLayout();
gridLayout.numColumns = 2;
ownerInfo.setLayout(gridLayout);
gridData = new GridData(GridData.HORIZONTAL_ALIGN_FILL);
gridData.horizontalSpan = 2;
ownerInfo.setLayoutData(gridData);
new Label(ownerInfo, SWT.NONE).setText("Name:");
ownerName = new Text(ownerInfo, SWT.SINGLE | SWT.BORDER);
ownerName.setLayoutData(new GridData(GridData.FILL_HORIZONTAL));
new Label(ownerInfo, SWT.NONE).setText("Phone:");
ownerPhone = new Text(ownerInfo, SWT.SINGLE | SWT.BORDER);
ownerPhone.setLayoutData(new GridData(GridData.FILL_HORIZONTAL));
Button enter = new Button(shell, SWT.PUSH);
enter.setText("Enter");
gridData = new GridData(GridData.HORIZONTAL_ALIGN_END);
gridData.horizontalSpan = 3;
enter.setLayoutData(gridData);
enter.addSelectionListener(new SelectionAdapter() {
public void widgetSelected(SelectionEvent event) {
System.out.println("/nDog Name: " + dogName.getText());
System.out.println("Dog Breed: " + dogBreed.getText());
System.out.println("Owner Name: " + ownerName.getText());
System.out.println("Owner Phone: " + ownerPhone.getText());
System.out.println("Categories:");
String cats[] = categories.getSelection();
for (int i = 0; i < cats.length; i++) {
System.out.println("/t" + cats[i]);
}
}
});
shell.pack();
shell.open();
while (!shell.isDisposed()) {
if (!display.readAndDispatch()) display.sleep();
}
if (dogImage != null) {
dogImage.dispose();
}
}
}
以下顯示了當Mary Smith輸入Fifi後的效果:
如果窗體尺寸變大,佈局重新調整爲如下所示:
注意以下內容:
l 一共有3列7行;
l dogPhoto Canvas可以變寬和變高,因爲它在橫向和縱向都設置了填充和擴展(本例沒有調整Image的大小,可以編程實現);
l dogBreed Combo可以變寬,因爲設置了它橫向填充,並且和Canvas在相同的列裏;
l dogName Text可以變寬,因爲設置了它橫向填充,並且它跨越的一列裏含有Canvas;
l ccategories List可以變高,因爲設置了它縱向填充,並且它跨越的行裏含有Canvas;
l 因爲categories List變高了,它的垂直滾動條消失了(它沒有變寬);
l ownerInfo Group變寬了,因爲設置了它橫向填充,且它跨越的一列裏含有Canvas;
l ownerInfo Group作爲Composite的子類,擁有自己的2行2列的GridLayout;
l ownerName和ownerPhone Texts變寬了,因爲Group變寬了,並且在Group的GridLayout裏設置了它們橫向填充和擴展;
l browse和delete 按鈕輕微交錯,由於設置了橫向填充,它們寬度保持一致;
l delete Button在它所在的行上靠上對齊;
l Categories標籤在categories List上居中對齊;
l enter按鈕在它跨越的三列裏水平右對齊;
l dogPhoto Canvas設置了寬度和高度初始值(width and height hints),因爲我們想儘可能的設置圖像大小爲80 x 80 像素;
l categories List設置了高度初始值,爲List字體高度的12倍,因爲我們想讓列表初始顯示12行。