网上说出现这个问题是因为api版本太高了，将版本调低就可以了
原本设置的是28，调到27和26都不行，于是一口气下了23 24 25，调成23就可以了，
调到24时报错：网上说因为24版本的Android为null。
java.lang.NoClassDefFoundError: com/android/util/PropertiesMap
at com.android.layoutlib.bridge.android.BridgeContext.createStyleBasedTypedArray(BridgeContext.java:940)
at com.android.layoutlib.bridge.android.BridgeContext.obtainStyledAttributes(BridgeContext.java:638)
at android.content.res.Resources_Theme_Delegate.obtainStyledAttributes(Resources_Theme_Delegate.java:71)
at android.content.res.Resources$Theme.obtainStyledAttributes(Resources.java:1436)
at android.widget.TextView.<init>(TextView.java:761)
at android.widget.TextView.<init>(TextView.java:704)
at android.widget.TextView.<init>(TextView.java:700)
at com.android.layoutlib.bridge.MockView.<init>(MockView.java:50)
at com.android.layoutlib.bridge.MockView.<init>(MockView.java:45)
at com.android.layoutlib.bridge.MockView.<init>(MockView.java:41)
at android.view.BridgeInflater.createViewFromTag(BridgeInflater.java:163)
at android.view.LayoutInflater.createViewFromTag(LayoutInflater.java:727)
at android.view.LayoutInflater.rInflate_Original(LayoutInflater.java:858)
at android.view.LayoutInflater_Delegate.rInflate(LayoutInflater_Delegate.java:70)
at android.view.LayoutInflater.rInflate(LayoutInflater.java:834)
at android.view.LayoutInflater.inflate(LayoutInflater.java:492)
at com.android.layoutlib.bridge.bars.CustomBar.<init>(CustomBar.java:95)
at com.android.layoutlib.bridge.bars.StatusBar.<init>(StatusBar.java:67)
at com.android.layoutlib.bridge.impl.Layout.createStatusBar(Layout.java:223)
at com.android.layoutlib.bridge.impl.Layout.<init>(Layout.java:145)
at com.android.layoutlib.bridge.impl.RenderSessionImpl.inflate(RenderSessionImpl.java:300)
at com.android.layoutlib.bridge.Bridge.createSession(Bridge.java:429)
at com.android.ide.common.rendering.LayoutLibrary.createSession(LayoutLibrary.java:350)
at com.android.tools.idea.rendering.RenderTask$2.compute(RenderTask.java:510)
at com.android.tools.idea.rendering.RenderTask$2.compute(RenderTask.java:498)
at com.intellij.openapi.application.impl.ApplicationImpl.runReadAction(ApplicationImpl.java:967)
at com.android.tools.idea.rendering.RenderTask.createRenderSession(RenderTask.java:498)
at com.android.tools.idea.rendering.RenderTask.access$600(RenderTask.java:72)
at com.android.tools.idea.rendering.RenderTask$3.call(RenderTask.java:610)
at com.android.tools.idea.rendering.RenderTask$3.call(RenderTask.java:607)
at com.android.tools.idea.rendering.RenderService.runRenderAction(RenderService.java:359)
at com.android.tools.idea.rendering.RenderTask.render(RenderTask.java:607)
at com.android.tools.idea.rendering.RenderTask.render(RenderTask.java:629)
at com.intellij.android.designer.designSurface.AndroidDesignerEditorPanel$7.run(AndroidDesignerEditorPanel.java:519)
at com.intellij.util.ui.update.MergingUpdateQueue.execute(MergingUpdateQueue.java:337)
at com.intellij.util.ui.update.MergingUpdateQueue.execute(MergingUpdateQueue.java:327)
at com.intellij.util.ui.update.MergingUpdateQueue$3.run(MergingUpdateQueue.java:271)
at com.intellij.util.ui.update.MergingUpdateQueue.flush(MergingUpdateQueue.java:286)
at com.intellij.util.ui.update.MergingUpdateQueue.flush(MergingUpdateQueue.java:244)
at com.intellij.util.ui.update.MergingUpdateQueue.run(MergingUpdateQueue.java:234)
at com.intellij.util.concurrency.QueueProcessor.runSafely(QueueProcessor.java:238)
at com.intellij.util.Alarm$Request$1.run(Alarm.java:352)
at java.util.concurrent.Executors$RunnableAdapter.call(Executors.java:511)
at java.util.concurrent.FutureTask.run(FutureTask.java:266)
at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1142)
at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:617)
at java.lang.Thread.run(Thread.java:748)
调到25 26 27 28都是报Failed to load platform rendering library的错误。