Android布局：看不到布局视图

Question

I just installed Android Studio 3 Preview Canary 6. I could not get a preview of the xml layout in activity_main.xml because of the following errors:

1. Render Problem
2. Failed to instantiate one or more classes

This also happened when I installed Canary 5. I thought that upgrading to Canary 6 would solve this issue but it didn't. Please help me fix it so I could start building my apps.

Here is my XML:

<?xml version="1.0" encoding="utf-8"?>
<android.support.constraint.ConstraintLayout 
xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:app="http://schemas.android.com/apk/res-auto"
    xmlns:tools="http://schemas.android.com/tools"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    tools:context="com.companyname.zooapp.MainActivity">

<TextView
    android:layout_width="wrap_content"
    android:layout_height="wrap_content"
    android:text="Hello World!"
    app:layout_constraintBottom_toBottomOf="parent"
    app:layout_constraintLeft_toLeftOf="parent"
    app:layout_constraintRight_toRightOf="parent"
    app:layout_constraintTop_toTopOf="parent" />

</android.support.constraint.ConstraintLayout>

Answer 1

You shouldn't post bugs of the Canary version of the Android Studio on StackOverflow. These type of questions and help you should receive in the android studio bugtracker.

Note that it is called a Canary version since it is full of bugs, and Google knows that, and they even know the bugs and explicitly say what are the bugs they know.

Check here to see the releases and bugs .

Answer 2

First of all make sure you are using the latest version ConstraintLayout dependency.

Preview section loads custom views fine as long as these views are correctly written. You have to remember about all small details like draw/onDraw/dispatchDraw methods, measuring and layouting, setting correct theme, styling, providing editMode data, etc.

The deal is that Android Studio has its own Context and Resources classes which are unable to perform certain things. For example these classes lack implementation of reading assets from assets folder and raw resources from raw folder.

To load a custom View, you need assets folder which you don't have access to in Android Studio. So make sure your custom icons file names are in lowercase and with the correct file extension.

Answer 3

I have found the solution to my own problem from the answer from an online community I asked about. Under the dependancies in the gradle build scripts, beta 1 should be used or lower. The current version of the support library beta 2 is quite buggy. Like this:

implementation 'com.android.support:appcompat-v7:26.0.0-beta1'