解读 LWUIT 之十：画笔（Painters）

解读 LWUIT 之十：画笔（Painters）

LWUIT 开发指南下载
作者写的 Hello Painter 源代码下载
        Painter 是一个用于在控件背景上进行绘制的接口。Painter 先把自己绘制出来，然后控件在屏幕的有效范围之内把自己绘制在 Painter 之上。使用 Painter 的最大优势之一就是我们可以任意绘制控件背景，比如实现控件的梯度背景，或者平铺背景（就是把一个图片平铺）。注意：为了可以看到 Painter 的绘制效果，我们必须把控件设置为一定程度的透明。
        举个例子。我们可以使用 Painter 在一个控件的背景上画一个对角线，源码如下：

package com.defonds.lwuit; import java.io.IOException; import com.sun.lwuit.Button; import com.sun.lwuit.Command; import com.sun.lwuit.Component; import com.sun.lwuit.Display; import com.sun.lwuit.Form; import com.sun.lwuit.Graphics; import com.sun.lwuit.Image; import com.sun.lwuit.Label; import com.sun.lwuit.Painter; import com.sun.lwuit.RadioButton; import com.sun.lwuit.animations.CommonTransitions; import com.sun.lwuit.geom.Rectangle; import com.sun.lwuit.layouts.BoxLayout; import com.sun.lwuit.plaf.UIManager; import com.sun.lwuit.util.Resources; public class HelloMidlet extends javax.microedition.midlet.MIDlet{ public void startApp() { // init the LWUIT Display Display.init(this); // Setting the application theme is discussed // later in the theme chapter and the resources chapter try { Resources r = Resources.open("/myresources.res"); UIManager.getInstance().setThemeProps(r.getTheme("myresources")); } catch (java.io.IOException e) {} Form exampleContainer = new Form("Form Title");// Create a Form Painter diagonalPainter = new Painter(){// Create a Painter public void paint(Graphics g, Rectangle rect){ g.drawLine(rect.getX(), rect.getY(), rect.getX() + rect.getSize().getWidth(), rect.getY() + rect.getSize().getHeight()); } }; Label myLabel = null;//declare a Label try { myLabel = new Label(Image.createImage("/duke.png"));//Create a Label } catch (IOException e) {e.printStackTrace();} myLabel.setAlignment(Component.CENTER);//set the alignment of the Label in the Form myLabel.getStyle().setBgTransparency(100);//set some level of transparency myLabel.getStyle().setBgPainter(diagonalPainter);//To use the diagonalPainter Button myButton = new Button("Image and Text Button");//Create a Button try { myButton.setIcon(Image.createImage("/duke.png"));//add an Icon to Button } catch (IOException e) {} myButton.setAlignment(Component.CENTER);//set the alignment of the Button in the Form myButton.getStyle().setBgTransparency(100);//set some level of transparency myButton.getStyle().setBgPainter(diagonalPainter);//To use the diagonalPainter RadioButton myRadioButton = new RadioButton("RadioButton");//Create a RadioButton myRadioButton.getStyle().setBgTransparency(100);//set some level of transparency myRadioButton.getStyle().setBgPainter(diagonalPainter);//To use the diagonalPainter exampleContainer.setLayout(new BoxLayout(BoxLayout.Y_AXIS));//Set LayoutManager exampleContainer.addComponent(myLabel);//Add a Label to the Form content pane exampleContainer.addComponent(myButton);//Add a Button to the Form content pane exampleContainer.addComponent(myRadioButton);//Add a RadioButton to the Form content pane exampleContainer.setTransitionOutAnimator(CommonTransitions.createFade(400));//Set Transitions animation of Fade exampleContainer.addCommand(new Command("Run", 2));//Add Command key exampleContainer.show();//Show it } public void pauseApp() {} public void destroyApp(boolean unconditional) {} }  
        运行效果图如下（注意 Painter 效果会被 Button 上的图片覆盖掉）：

        有时单个 Painter 不能满足复杂逻辑需要的画法，这时可以使用 PainterChain 把几个 Painter 绑在一起作为一个进行展现。PainterChain 把 Painter 进行责任分工，比如一个 Painter 负责绘制背景图片而另一个 Painter 负责将验证错误信息高亮显示。可以这样创建一个 PainterChain：PainterChain chain = new PainterChain(new Painter[]{painter1, painter2});
        上面的效果图演示的是 Painter 绘制在容器背景之上，如果控件非透明，就看不到 Painter 效果。那么可否将 Painter 效果绘制在控件之上呢？可以使用 Glass Pane。Glass Pane 是一种绘制在容器之上的 Painter。使用 Glass Pane 可以为我们的应用程序创建特别的视觉特效。可以使用 PainterChain 来安装 Glass Pane 以防止其将已经安装的 Glass Pane 给替换掉。
        一般使用类似于下面的代码来安装使用 Glass Pane：
Painter glassPane = ...; myForm.setGlassPane(glassPane); 
        使用 PainterChain 安装 Glass Pane 以防止已经安装的 Glass Pane 被替换（这种方法在没有任何 Glass Pane 对象被事先安装的情况下也可以用）：
Painter glassPane = ...; PainterChain.installGlassPane(myForm, glassPane);