想实现一个sleep一会再更新UI的操作，结果报错了。最后使用android.os.Handler来实现这个功能本文就分享一下解决这个报错的办法
工具/原料
AndroidStudio
Java
Android真机
方法/步骤
1、要实现的功能：在App上点击”变透明“的按钮后，App的背景色先变为透明，等等10秒后，再把背景色改为半透明（alpha值为0.5）Showthecode:AndroidManifest.xml:<LinearLayoutandroid:layout_width="fill_parent"android:layout_height="wrap_content"android:gravity="center"android:orientation="horizontal"><Buttonandroid:id="@+id/clickTransparency"android:layout_width="wrap_content"android:layout_height="wrap_content"android:onClick="turnTransparencyClickHandler"android:text="变透明"/>MainActivity.javapublicvoidturnTransparencyClickHandler(Viewview){changeBackgroundAlphaTo(0.0f);}privatevoidchangeBackgroundAlphaTo(finalfloatalphaValue){newThread(newRunnable(){@Overridepublicvoidrun(){finalWindowManager.LayoutParamsattributes=getWindow().getAttributes();attributes.alpha=alphaValue;//０.０全透明．１.０不透明．getWindow().setAttributes(attributes);}}).start();}
2、执行上述代码。在App中点击”变透明“的按钮后，App就退出了。logcat中打印了这个错：03-2014:47:31.32611640-11796/com.example.cy.myapplicationE/AndroidRuntime:FATALEXCEPTION:Thread-1565103-2014:47:31.32611640-11796/com.example.cy.myapplicationE/AndroidRuntime:Process:com.example.cy.myapplication,PID:1164003-2014:47:31.32611640-11796/com.example.cy.myapplicationE/AndroidRuntime:android.view.ViewRootImpl$CalledFromWrongThreadException:Onlytheoriginalthreadthatcreatedaviewhierarchycantouchitsviews.03-2014:47:31.32611640-11796/com.example.cy.myapplicationE/AndroidRuntime:atandroid.view.ViewRootImpl.checkThread(ViewRootImpl.java:6090)03-2014:47:31.32611640-11796/com.example.cy.myapplicationE/AndroidRuntime:atandroid.view.ViewRootImpl.requestLayout(ViewRootImpl.java:879)03-2014:47:31.32611640-11796/com.example.cy.myapplicationE/AndroidRuntime:atandroid.view.View.requestLayout(View.java:16463)03-2014:47:31.32611640-11796/com.example.cy.myapplicationE/AndroidRuntime:atandroid.view.View.setLayoutParams(View.java:10593)03-2014:47:31.32611640-11796/com.example.cy.myapplicationE/AndroidRuntime:atandroid.view.WindowManagerGlobal.updateViewLayout(WindowManagerGlobal.java:292)03-2014:47:31.32611640-11796/com.example.cy.myapplicationE/AndroidRuntime:atandroid.view.WindowManagerImpl.updateViewLayout(WindowManagerImpl.java:74)03-2014:47:31.32611640-11796/com.example.cy.myapplicationE/AndroidRuntime:atandroid.app.Activity.onWindowAttributesChanged(Activity.java:2347)03-2014:47:31.32611640-11796/com.example.cy.myapplicationE/AndroidRuntime:atandroid.support.v7.internal.view.WindowCallbackWrapper.onWindowAttributesChanged(WindowCallbackWrapper.java:105)03-2014:47:31.32611640-11796/com.example.cy.myapplicationE/AndroidRuntime:atandroid.view.Window.setAttributes(Window.java:847)03-2014:47:31.32611640-11796/com.example.cy.myapplicationE/AndroidRuntime:atcom.example.cy.myapplication.MainActivity$1.run(MainActivity.java:78)03-2014:47:31.32611640-11796/com.example.cy.myapplicationE/AndroidRuntime:atjava.lang.Thread.run(Thread.java:841)
3、和Swing中的用法还不一样啊。哪就在UI线程中更新吧。Android中有个组件android.os.Handler的postDelayed可以解决这个问题源码:/***CausestheRunnablertobeaddedtothemessagequeue,toberun*afterthespecifiedamountoftimeelapses.*Therunnablewillberunonthethreadtowhichthishandler*isattached.*<b>Thetime-baseis{@linkandroid.os.SystemClock#uptimeMillis}.</b>*Timespentindeepsleepwilladdanadditionaldelaytoexecution.**@paramrTheRunnablethatwillbeexecuted.*@paramdelayMillisThedelay(inmilliseconds)untiltheRunnable*willbeexecuted.**@returnReturnstrueiftheRunnablewassuccessfullyplacedintothe*messagequeue.Returnsfalseonfailure,usuallybecausethe*looperprocessingthemessagequeueisexiting.Notethata*resultoftruedoesnotmeantheRunnablewillbeprocessed--*ifthelooperisquitbeforethedeliverytimeofthemessage*occursthenthemessagewillbedropped.*/publicfinalbooleanpostDelayed(Runnabler,longdelayMillis){returnsendMessageDelayed(getPostMessage(r),delayMillis);}
4、改改刚才报错的代码Code:MainActivity.java:定义一个字段privateHandlerhandler=newHandler();publicvoidturnTransparencyClickHandler(Viewview){changeBackgroundAlphaTo(0.0f);handler.postDelayed(newRunnable(){@Overridepublicvoidrun(){Log.i("turnTransparency","begintochangealphato0.5");changeBackgroundAlphaTo(0.5f);Log.i("turnTransparency","endtochangealphato0.5");}},10*1000);}privatevoidchangeBackgroundAlphaTo(floatalphaValue){WindowManager.LayoutParamsattributes=getWindow().getAttributes();attributes.alpha=alphaValue;//０.０全透明．１.０不透明．getWindow().setAttributes(attributes);}
5、执行下,看看是否达到预期效果达到了，Success！
6、从截图看不出这个变化。在执行变成半透明的代码中，加有日志打印，在logcat中看看能否找到日志：03-2015:16:14.98616571-16571/com.example.cy.myapplicationI/turnTransparency:begintochangealphato0.503-2015:16:14.98616571-16571/com.example.cy.myapplicationI/turnTransparency:endtochangealphato0.5
