代码： -
public class DigitalDial extends View{
private Paint titlePaint;
private String title;
private Float value ;
public DigitalDial(Context context) {
super(context);
// TODO Auto-generated constructor stub
}
public DigitalDial(Context context, AttributeSet attrs) {
super(context, attrs);
}
public DigitalDial(Context context, AttributeSet attrs, int defStyle) {
super(context, attrs, defStyle);
}
public void setValue(float value) {
this.value = value;
invalidate();
}
@Override
protected void onDraw(Canvas canvas) {
super.onDraw(canvas);
// draw some text using FILL style
titlePaint = new Paint();
titlePaint.setStyle(Paint.Style.FILL);
titlePaint.setTypeface(Typeface.DEFAULT_BOLD);
//paint.setTextAlign(Paint.Align.RIGHT);
titlePaint.setColor(Color.YELLOW);
titlePaint.setAntiAlias(true);
titlePaint.setTextSize(28);
drawTitle(canvas);
}
public void setTitle(String title) {
this.title = title;
}
private String getTitle() {
return title;
}
public void drawTitle(Canvas canvas) {
String title = getTitle();
canvas.drawText(title,30, 48, titlePaint);
}
}
访问图形布局时出错： - java.lang.NullPointerException
调试时显示错误：titlePaint为null，但为什么????
帮助表示赞赏。
抱歉代码不完整。缺少代码段; -
package pkg.digitalDial;
import android.app.Activity;
import android.os.Bundle;
import android.os.CountDownTimer;
import pkg.digitalDial.DigitalDial;
public class DigitalDialActivity extends Activity {
/** Called when the activity is first created. */
DigitalDial speedDial ;
CountDownTimer speedTimer;
@Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.digitaldial);
speedDial = (DigitalDial) findViewById(R.id.dial1);
speedDial.setTitle("Speed");
speedDial.setValue(2.0f);
}
}
错误日志： -
java.lang.NullPointerException
at android.graphics.Canvas_Delegate.drawText(Canvas_Delegate.java:276)
at android.graphics.Canvas.drawText(Canvas.java)
at pkg.digitalDial.DigitalDial.drawTitle(DigitalDial.java:62)
at pkg.digitalDial.DigitalDial.onDraw(DigitalDial.java:48)
at android.view.View.draw(View.java:6740)
at android.view.ViewGroup.drawChild(ViewGroup.java:1640)
at android.view.ViewGroup.dispatchDraw(ViewGroup.java:1367)
at android.view.ViewGroup.drawChild(ViewGroup.java:1638)
at android.view.ViewGroup.dispatchDraw(ViewGroup.java:1367)
at android.view.ViewGroup.drawChild(ViewGroup.java:1638)
at android.view.ViewGroup.dispatchDraw(ViewGroup.java:1367)
at android.view.View.draw(View.java:6743)
at android.view.ViewGroup.drawChild(ViewGroup.java:1640)
at android.view.ViewGroup.dispatchDraw(ViewGroup.java:1367)
at android.view.View.draw(View.java:6743)
at com.android.layoutlib.bridge.impl.RenderSessionImpl.render(RenderSessionImpl.java:466)
at com.android.layoutlib.bridge.Bridge.createSession(Bridge.java:320)
at com.android.ide.common.rendering.LayoutLibrary.createSession(LayoutLibrary.java:325)
at com.android.ide.eclipse.adt.internal.editors.layout.gle2.RenderService.createRenderSession(RenderService.java:380)
at com.android.ide.eclipse.adt.internal.editors.layout.gle2.GraphicalEditorPart.renderWithBridge(GraphicalEditorPart.java:1310)
at com.android.ide.eclipse.adt.internal.editors.layout.gle2.GraphicalEditorPart.recomputeLayout(GraphicalEditorPart.java:1075)
at com.android.ide.eclipse.adt.internal.editors.layout.gle2.GraphicalEditorPart.activated(GraphicalEditorPart.java:901)
at com.android.ide.eclipse.adt.internal.editors.layout.LayoutEditor.pageChange(LayoutEditor.java:403)
at org.eclipse.ui.part.MultiPageEditorPart.setActivePage(MultiPageEditorPart.java:1076)
at org.eclipse.ui.forms.editor.FormEditor.setActivePage(FormEditor.java:601)
at com.android.ide.eclipse.adt.internal.editors.AndroidXmlEditor.selectDefaultPage(AndroidXmlEditor.java:314)
at com.android.ide.eclipse.adt.internal.editors.AndroidXmlEditor.addPages(AndroidXmlEditor.java:219)
at org.eclipse.ui.forms.editor.FormEditor.createPages(FormEditor.java:138)
at org.eclipse.ui.part.MultiPageEditorPart.createPartControl(MultiPageEditorPart.java:357)
at org.eclipse.ui.internal.EditorReference.createPartHelper(EditorReference.java:662)
at org.eclipse.ui.internal.EditorReference.createPart(EditorReference.java:462)
at org.eclipse.ui.internal.WorkbenchPartReference.getPart(WorkbenchPartReference.java:595)
at org.eclipse.ui.internal.EditorReference.getEditor(EditorReference.java:286)
at org.eclipse.ui.internal.WorkbenchPage.busyOpenEditorBatched(WorkbenchPage.java:2857)
at org.eclipse.ui.internal.WorkbenchPage.busyOpenEditor(WorkbenchPage.java:2762)
at org.eclipse.ui.internal.WorkbenchPage.access$11(WorkbenchPage.java:2754)
at org.eclipse.ui.internal.WorkbenchPage$10.run(WorkbenchPage.java:2705)
at org.eclipse.swt.custom.BusyIndicator.showWhile(BusyIndicator.java:70)
at org.eclipse.ui.internal.WorkbenchPage.openEditor(WorkbenchPage.java:2701)
at org.eclipse.ui.internal.WorkbenchPage.openEditor(WorkbenchPage.java:2685)
at org.eclipse.ui.internal.WorkbenchPage.openEditor(WorkbenchPage.java:2676)
at org.eclipse.ui.ide.IDE.openEditor(IDE.java:651)
at org.eclipse.ui.ide.IDE.openEditor(IDE.java:610)
at org.eclipse.jdt.internal.ui.javaeditor.EditorUtility.openInEditor(EditorUtility.java:361)
at org.eclipse.jdt.internal.ui.javaeditor.EditorUtility.openInEditor(EditorUtility.java:168)
at org.eclipse.jdt.ui.actions.OpenAction.run(OpenAction.java:229)
at org.eclipse.jdt.ui.actions.OpenAction.run(OpenAction.java:208)
at org.eclipse.jdt.ui.actions.SelectionDispatchAction.dispatchRun(SelectionDispatchAction.java:274)
at org.eclipse.jdt.ui.actions.SelectionDispatchAction.run(SelectionDispatchAction.java:250)
at org.eclipse.jdt.internal.ui.packageview.PackageExplorerActionGroup.handleOpen(PackageExplorerActionGroup.java:373)
at org.eclipse.jdt.internal.ui.packageview.PackageExplorerPart$4.open(PackageExplorerPart.java:526)
at org.eclipse.ui.OpenAndLinkWithEditorHelper$InternalListener.open(OpenAndLinkWithEditorHelper.java:48)
at org.eclipse.jface.viewers.StructuredViewer$2.run(StructuredViewer.java:842)
at org.eclipse.core.runtime.SafeRunner.run(SafeRunner.java:42)
at org.eclipse.core.runtime.Platform.run(Platform.java:888)
at org.eclipse.ui.internal.JFaceUtil$1.run(JFaceUtil.java:48)
at org.eclipse.jface.util.SafeRunnable.run(SafeRunnable.java:175)
at org.eclipse.jface.viewers.StructuredViewer.fireOpen(StructuredViewer.java:840)
at org.eclipse.jface.viewers.StructuredViewer.handleOpen(StructuredViewer.java:1101)
at org.eclipse.jface.viewers.StructuredViewer$6.handleOpen(StructuredViewer.java:1205)
at org.eclipse.jface.util.OpenStrategy.fireOpenEvent(OpenStrategy.java:264)
at org.eclipse.jface.util.OpenStrategy.access$2(OpenStrategy.java:258)
at org.eclipse.jface.util.OpenStrategy$1.handleEvent(OpenStrategy.java:298)
at org.eclipse.swt.widgets.EventTable.sendEvent(EventTable.java:84)
at org.eclipse.swt.widgets.Widget.sendEvent(Widget.java:1003)
at org.eclipse.swt.widgets.Display.runDeferredEvents(Display.java:3880)
at org.eclipse.swt.widgets.Display.readAndDispatch(Display.java:3473)
at org.eclipse.ui.internal.Workbench.runEventLoop(Workbench.java:2405)
at org.eclipse.ui.internal.Workbench.runUI(Workbench.java:2369)
at org.eclipse.ui.internal.Workbench.access$4(Workbench.java:2221)
at org.eclipse.ui.internal.Workbench$5.run(Workbench.java:500)
at org.eclipse.core.databinding.observable.Realm.runWithDefault(Realm.java:332)
at org.eclipse.ui.internal.Workbench.createAndRunWorkbench(Workbench.java:493)
at org.eclipse.ui.PlatformUI.createAndRunWorkbench(PlatformUI.java:149)
at org.eclipse.ui.internal.ide.application.IDEApplication.start(IDEApplication.java:113)
at org.eclipse.equinox.internal.app.EclipseAppHandle.run(EclipseAppHandle.java:194)
at org.eclipse.core.runtime.internal.adaptor.EclipseAppLauncher.runApplication(EclipseAppLauncher.java:110)
at org.eclipse.core.runtime.internal.adaptor.EclipseAppLauncher.start(EclipseAppLauncher.java:79)
at org.eclipse.core.runtime.adaptor.EclipseStarter.run(EclipseStarter.java:368)
at org.eclipse.core.runtime.adaptor.EclipseStarter.run(EclipseStarter.java:179)
at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
at sun.reflect.NativeMethodAccessorImpl.invoke(Unknown Source)
at sun.reflect.DelegatingMethodAccessorImpl.invoke(Unknown Source)
at java.lang.reflect.Method.invoke(Unknown Source)
at org.eclipse.equinox.launcher.Main.invokeFramework(Main.java:559)
at org.eclipse.equinox.launcher.Main.basicRun(Main.java:514)
at org.eclipse.equinox.launcher.Main.run(Main.java:1311)
答案 0 :(得分：1)
当您寻求有关异常的帮助时，发布完整堆栈跟踪始终是个好主意。这样，我们就可以更容易地找出确切的问题！
如果没有，我们只能猜测，但如果这是您的所有代码，我猜NullPointerException来自title字段。这里：
public void drawTitle(Canvas canvas) {
String title = getTitle();
canvas.drawText(title,30, 48, titlePaint);
}
您正在使用title的值，我没有看到它在任何地方初始化。 String引用很可能是null。
答案 1 :(得分：1)
您需要将绘画设置移动到构造函数中：
public DigitalDial(Context context) {
super(context);
titlePaint = new Paint();
titlePaint.setStyle(Paint.Style.FILL);
titlePaint.setTypeface(Typeface.DEFAULT_BOLD);
//paint.setTextAlign(Paint.Align.RIGHT);
titlePaint.setColor(Color.YELLOW);
titlePaint.setAntiAlias(true);
titlePaint.setTextSize(28);
}
您正在使用每次绘制创建一个新的绘制对象，这对效率非常不利。您也不需要重载构造函数，因为您知道如何实例化自定义视图，并且您不太可能在应用程序中以三种不同的方式执行此操作。
在第一次绘制瓷砖时，圣地亚哥是正确的，因此你应该在顶部说：
private String title =“”;