Android工具中的“预览”选项卡中未显示UI工具

Question

我正在创建一个hello android app，并在预览标签中显示相同的布局。

我已经多次安装并重新安装android studio并完成了这样无用的步骤无济于事，但无法获得那个显示器。我怎么知道的？

如果有帮助，也会遇到此异常：

null
java.lang.NullPointerException
at                                                        com.intellij.android.designer.designSurface.AndroidDesignerEditorPanel.hasAlphaChannel(AndroidDesignerEditorPanel.java:1386)
at com.android.tools.idea.rendering.multi.RenderPreview.createErrorThumbnail(RenderPreview.java:769)
at com.android.tools.idea.rendering.multi.RenderPreview.tryRenderSync(RenderPreview.java:606)
at com.android.tools.idea.rendering.multi.RenderPreview.renderSync(RenderPreview.java:531)
at com.android.tools.idea.rendering.multi.RenderPreviewManager$3.run(RenderPreviewManager.java:1382)
at com.intellij.util.concurrency.QueueProcessor.runSafely(QueueProcessor.java:238)
at com.intellij.util.Alarm$Request$1.run(Alarm.java:351)
at java.util.concurrent.Executors$RunnableAdapter.call(Executors.java:511)
at java.util.concurrent.FutureTask.run(FutureTask.java:266)
at com.intellij.util.concurrency.QueueProcessor$RunnableConsumer.consume(QueueProcessor.java:298)
at com.intellij.util.concurrency.QueueProcessor$RunnableConsumer.consume(QueueProcessor.java:295)
at com.intellij.util.concurrency.QueueProcessor$2$1.run(QueueProcessor.java:110)
at com.intellij.util.concurrency.QueueProcessor.runSafely(QueueProcessor.java:238)
at com.intellij.util.concurrency.QueueProcessor$2.consume(QueueProcessor.java:107)
at com.intellij.util.concurrency.QueueProcessor$2.consume(QueueProcessor.java:104)
at com.intellij.util.concurrency.QueueProcessor$3$1.run(QueueProcessor.java:215)
at com.intellij.util.concurrency.QueueProcessor.runSafely(QueueProcessor.java:238)
at com.intellij.util.concurrency.QueueProcessor$3.run(QueueProcessor.java:212)
at com.intellij.openapi.application.impl.ApplicationImpl$8.run(ApplicationImpl.java:400)
at java.util.concurrent.Executors$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:745)
at org.jetbrains.ide.PooledThreadE