I have a problem, I installed Android Studio on my PC with windows 10 64 bits, but when I started to make a project I realized that my components were not shown (buttons, texts etc in the preview, I do not know how to fix this problem I hope you can help me. 
in the build.gradle changes alpha3 to alpha1 with api 28 as it originally came. luck !!
implementation 'com.android.support:appcompat-v7:28.0.0-alpha1'
implementation 'com.android.support:design:28.0.0-alpha1'
A similar question was published:
I can not see nothing on the screen design. (Android Studio)
but in this case the error is:
failed to load AppCompat ActionBar with unknown error
I suggest you have as minimum configuration:
use:
dependencies {
...
implementation 'com.android.support:appcompat-v7:26.1.0'
...
}
with:
compileSdkVersion 26
buildToolsVersion "26.0.1"
and within the build.gradle file located in the root of the project, use minimum gradle version 3.0.1:
buildscript {
...
....
dependencies {
classpath 'com.android.tools.build:gradle:3.0.1'
...
...
}
}
Many times the performance problem is because the version of the API in the editor is greater than the one for which your app is designed and with downloading it you can usually see the elements, both in the design view and in the preview of the text view of the layout.
You can download it in the top menu in green button of android (API version in editor) in which it says that you are in version 28.