Android Studio（1.5.1）-错误：找不到符号类/应用程序将无法运行

Question

I'm working on my first Android application. It's a very simple farenheit/celsius converter, and all of my IDs, methods, and buttons/text fields are perfectly copied out. I triple checked. (I'm following instructions from a video my professor posted.) However, I'm having difficulty trying to get Android Studio to run the application.

I've found plenty of questions similar to this one and many of them suggest synchronizing the gradle files . So I did. I'm still getting these same error messages:

---

Here is the app information:

Code from app/res/layout/content_test.xml:

<?xml version="1.0" encoding="utf-8"?>
<RelativeLayout 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"
    android:paddingBottom="@dimen/activity_vertical_margin"
    android:paddingLeft="@dimen/activity_horizontal_margin"
    android:paddingRight="@dimen/activity_horizontal_margin"
    android:paddingTop="@dimen/activity_vertical_margin"
    app:layout_behavior="@string/appbar_scrolling_view_behavior"
    tools:context="john.testapplication.TestActivity"
    tools:showIn="@layout/activity_test">

    <EditText
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:inputType="numberDecimal"
        android:ems="10"
        android:id="@+id/temperatureEditText"
        android:layout_alignParentTop="true"
        android:layout_alignParentLeft="true"
        android:layout_alignParentStart="true"
        android:hint="Enter Temperature" />

    <RadioGroup
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:layout_below="@+id/temperatureEditText"
        android:layout_alignParentLeft="true"
        android:layout_alignParentStart="true"
        android:id="@+id/radioGroup">

        <RadioButton
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:text="From Celsius to Farenheit"
            android:id="@+id/toFarenheitRadioButton"
            android:checked="false" />

        <RadioButton
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:text="From Farenheit to Celsius"
            android:id="@+id/toCelsiusRadioButton"
            android:checked="false" />
    </RadioGroup>

    <Button
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text="Convert"
        android:id="@+id/convertButton"
        android:layout_below="@+id/radioGroup"
        android:layout_alignParentLeft="true"
        android:layout_alignParentStart="true"
        android:onClick="convert" />
</RelativeLayout>

Code from app/res/layout/activitytest.xml: ( I thought I was using Relative Layout , I don't know if this has anything to do with my problem )

<?xml version="1.0" encoding="utf-8"?>
<android.support.design.widget.CoordinatorLayout 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"
    android:fitsSystemWindows="true"
    tools:context="john.testapplication.TestActivity">

    <android.support.design.widget.AppBarLayout
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:theme="@style/AppTheme.AppBarOverlay">

        <android.support.v7.widget.Toolbar
            android:id="@+id/toolbar"
            android:layout_width="match_parent"
            android:layout_height="?attr/actionBarSize"
            android:background="?attr/colorPrimary"
            app:popupTheme="@style/AppTheme.PopupOverlay" />

    </android.support.design.widget.AppBarLayout>

    <include layout="@layout/content_test" />

    <android.support.design.widget.FloatingActionButton
        android:id="@+id/fab"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_gravity="bottom|end"
        android:layout_margin="@dimen/fab_margin"
        android:src="@android:drawable/ic_dialog_email" />

</android.support.design.widget.CoordinatorLayout>

Again, I was building this app from a video my instructor gave me, so I'm willing to bet it has something to do with my version of Android Studio or settings on my computer as opposed to code itself.

Answer 1

Okay, with some help from someone on this site, I found a solution. Apparently in TestActivity.xml, I forgot to import these:

import android.widget.EditText;
import android.widget.RadioButton;

Fixed everything. I had assumed it was already all imported. Thanks to Eugen Pechanec for the helpful tips.

Answer 2

Make sure you are importing the correct libraries. Also once correctly imported

initialize radioButtons :
RadioButton rd;

In the onCreate method:

rd = (RadioButton)findViewById(R.id.radioButton);