Android Studio中创建colors.xml后如何正确访问颜色属性？

问题背景 #

我在Android Studio的res目录下新建了名为color的文件夹：

随后在该color文件夹内创建了colors.xml文件，内容如下：

<?xml version="1.0" encoding="utf-8"?>
<selector xmlns:tools="http://schemas.android.com/tools" xmlns:android="http://schemas.android.com/apk/res/android">
<resources>
    <color android:name="default_screen_bg" tools:ignore="ExtraText">#f9f9f9</color>
    <color android:name="rounded_container_bg">#222222</color>
    <color android:name="rounded_container_border">#3b3f44</color>
    <color android:name="light_gray_header_color">#646663</color>
</resources>
</selector>

接着尝试在res/drawable目录下的另一个xml文件中访问colors.xml里的颜色属性，代码如下：

<?xml version="1.0" encoding="UTF-8"?>
<inset android:insetLeft="1.0px" android:insetRight="1.0px" android:insetTop="0.0px" android:insetBottom="1.0px"
    xmlns:android="http://schemas.android.com/apk/res/android">
    <selector>
        <item android:state_pressed="true">
            <shape>
                <gradient android:startColor="@color/rounded_container_bg" android:endColor="@color/rounded_container_bg" android:angle="270.0" />
                <corners android:radius="11.0dip" />
            </shape>
        </item>
        <item>
            <shape>
                <stroke android:width="1.0px" android:color="@color/rounded_container_border" />
                <gradient android:startColor="@color/colors/rounded_container_bg" android:endColor="@color/rounded_container_bg" android:angle="270.0" />
                <corners android:radius="10.0dip" />

            </shape>
        </item>
    </selector>
</inset>

但代码中@color/colors相关行出现红色报错：

附MainActivity的Kotlin代码：

package com.example.flashlight

import android.content.Context
import android.hardware.camera2.CameraAccessException
import android.hardware.camera2.CameraManager
import android.os.Bundle
import android.os.Handler
import android.os.Looper
import android.widget.SeekBar
import androidx.appcompat.app.AppCompatActivity


class MainActivity : AppCompatActivity() {
    var flashLightStatus: Boolean = false

    override fun onCreate(savedInstanceState: Bundle?) {
        super.onCreate(savedInstanceState)
        setContentView(R.layout.activity_main)
        startFlashLight()
    }

    private fun openFlashLight() {
        val cameraManager = getSystemService(Context.CAMERA_SERVICE) as CameraManager
        val cameraId = cameraManager.cameraIdList[0]
        if (!flashLightStatus) {
            try {
                cameraManager.setTorchMode(cameraId, true)
                flashLightStatus = true

            } catch (e: CameraAccessException) {
            }
        } else {
            try {
                cameraManager.setTorchMode(cameraId, false)
                flashLightStatus = false
            } catch (e: CameraAccessException) {
            }
        }
    }

    private fun closeFlashLight()
    {
        val cameraManager = getSystemService(Context.CAMERA_SERVICE) as CameraManager
        val cameraId = cameraManager.cameraIdList[0]
        if (flashLightStatus) {
            try {
                cameraManager.setTorchMode(cameraId, false)
                flashLightStatus = false

            } catch (e: CameraAccessException) {
            }
        } else {
            try {
                cameraManager.setTorchMode(cameraId, true)
                flashLightStatus = true
            } catch (e: CameraAccessException) {
            }
        }
    }

    fun startFlashLight() {

        var flashLightOn = false

        openFlashLight()
        flashLightOn = true

        val handler = Handler(Looper.getMainLooper())
        handler.postDelayed(object: Runnable {
            override fun run() {
                if (flashLightOn) {
                    closeFlashLight()
                } else {
                    openFlashLight()
                }

                // 切换状态并5秒后再次执行
                flashLightOn = !flashLightOn
                handler.postDelayed(this, 5000)
            }
        }, 5000)
    }
}

解决步骤 #

1. 修正colors.xml的根标签错误 #

颜色资源文件的根标签必须是<resources>，当前用<selector>作为根标签会导致系统无法识别颜色资源。修改后的colors.xml：

<?xml version="1.0" encoding="utf-8"?>
<resources xmlns:tools="http://schemas.android.com/tools" xmlns:android="http://schemas.android.com/apk/res/android">
    <color android:name="default_screen_bg" tools:ignore="ExtraText">#f9f9f9</color>
    <color android:name="rounded_container_bg">#222222</color>
    <color android:name="rounded_container_border">#3b3f44</color>
    <color android:name="light_gray_header_color">#646663</color>
</resources>

2. 修正颜色引用路径错误 #

在drawable的xml文件中，无需在颜色引用里添加文件夹名colors，直接使用颜色资源名称即可。把错误的@color/colors/rounded_container_bg改成@color/rounded_container_bg，修改后的对应代码行：

<gradient android:startColor="@color/rounded_container_bg" android:endColor="@color/rounded_container_bg" android:angle="270.0" />

3. 清理并重建项目 #

修改完成后，点击Android Studio顶部菜单栏的Build -> Clean Project，完成后再点击Build -> Rebuild Project，即可消除报错。

内容的提问来源于stack exchange，提问作者Daniel Lip