找到了解决方案。

将此代码添加到build.gradle中，

dependencies {
    def multidex_version = "2.0.1"
    implementation 'androidx.multidex:multidex:$multidex_version'
}

then enable the multidex to true

 defaultConfig {
        ...
        minSdkVersion 15 
        targetSdkVersion 28
        multiDexEnabled true
    }

当你试图构建一个使用VectorDrawable作为自适应图标的应用程序时，你可能会遇到这样的错误。和你的XML文件包含"android:fillColor"与<梯度>块:

res - drawable icon_with_gradient xml。

<?xml version="1.0" encoding="utf-8"?>
<vector xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:aapt="http://schemas.android.com/aapt"
    android:width="96dp"
    android:height="96dp"
    android:viewportHeight="100"
    android:viewportWidth="100">

    <path
        android:pathData="M1,1 H99 V99 H1Z"
        android:strokeColor="?android:attr/colorAccent"
        android:strokeWidth="2">
        <aapt:attr name="android:fillColor">
            <gradient
                android:endColor="#156a12"
                android:endX="50"
                android:endY="99"
                android:startColor="#1e9618"
                android:startX="50"
                android:startY="1"
                android:type="linear" />
        </aapt:attr>
    </path>
</vector>

渐变填充颜色通常用于自适应图标，例如在教程中这里，这里和这里。

即使布局预览工作正常，当你构建应用程序时，你会看到这样的错误:

FAILURE: Build failed with an exception.

* What went wrong:
Execution failed for task ':app:mergeDebugResources'.
> A failure occurred while executing com.android.build.gradle.internal.tasks.Workers$ActionFacade
   > Error while processing Project/app/src/main/res/drawable/icon_with_gradient.xml : null

(More info shown when the gradle build is run with --stack-trace flag):

Caused by: java.lang.NullPointerException
    at com.android.ide.common.vectordrawable.VdPath.addGradientIfExists(VdPath.java:614)
    at com.android.ide.common.vectordrawable.VdTree.parseTree(VdTree.java:149)
    at com.android.ide.common.vectordrawable.VdTree.parse(VdTree.java:129)
    at com.android.ide.common.vectordrawable.VdParser.parse(VdParser.java:39)
    at com.android.ide.common.vectordrawable.VdPreview.getPreviewFromVectorXml(VdPreview.java:197)
    at com.android.builder.png.VectorDrawableRenderer.generateFile(VectorDrawableRenderer.java:224)
    at com.android.build.gradle.tasks.MergeResources$MergeResourcesVectorDrawableRenderer.generateFile(MergeResources.java:413)
    at com.android.ide.common.resources.MergedResourceWriter$FileGenerationWorkAction.run(MergedResourceWriter.java:409)

解决方案是将文件icon_with_gradient.xml移动到drawable-v24/icon_with_gradient.xml或drawable-v26/icon_with_gradient.xml。这是因为梯度填充只在API 24 (Android 7)及以上版本中支持。VectorDrawable:无效的可绘制标签梯度

几分钟前，当我试图在我的C/(.something. /.something. /.something. /.something....)目录中运行一个flutter项目时，我也遇到了同样的问题，

所以我在我的E目录中创建了一个新文件夹，并在那里启动了一个新项目，当我运行它.....令人惊讶的是，它竟然起作用了。我不知道为什么?

这是我在运行E: directory后得到的消息

Launching lib\main.dart on Lenovo K33a42 in debug mode...
Running Gradle task 'assembleDebug'...
Checking the license for package Android SDK Platform 28 in 
C:\Users\Shankar\AppData\Local\Android\sdk\licenses
License for package Android SDK Platform 28 accepted.
Preparing "Install Android SDK Platform 28 (revision: 6)".
"Install Android SDK Platform 28 (revision: 6)" ready.
Installing Android SDK Platform 28 in 
C:\Users\Shankar\AppData\Local\Android\sdk\platforms\android-28
"Install Android SDK Platform 28 (revision: 6)" complete.
"Install Android SDK Platform 28 (revision: 6)" finished.
Parameter format not correct -
√ Built build\app\outputs\apk\debug\app-debug.apk.
Installing build\app\outputs\apk\app.apk...
Debug service listening on ws://127.0.0.1:51105/5xCsT5vV62M=/ws
Syncing files to device Lenovo K33a42...

我通过添加以下行来解决这个问题

在android>应用>build中添加multiDexEnabled truegradle在defaultConfig里面 在android>应用>构建中添加实现'com.android.support:multidex:1.0.3'。Gradle内部依赖

gradle.proprites

org.gradle.jvmargs=-Xmx1536M

build.gradle

defaultConfig {
        multiDexEnabled true
    }

dependencies {
    implementation 'com.android.support:multidex:1.0.3'
}

然而这些东西并没有解决我的问题，直到我增加编译esdkversion从27到28，它为我工作。

android {
    compileSdkVersion 28

    sourceSets {
        main.java.srcDirs += 'src/main/kotlin'
    }

    lintOptions {
        disable 'InvalidPackage'
    }

    defaultConfig {
         minSdkVersion 21
        targetSdkVersion 28
        versionCode flutterVersionCode.toInteger()
        versionName flutterVersionName
        multiDexEnabled true
    }

    buildTypes {
        release {
            crunchPngs false
        }
    }
}

这里我发现只需添加这一行gradle.properties

org . gradle jvmargs = -Xmx4g。