java – 错误： – 执行失败的任务’：app：dexDebug’在android工作室

我新安装的 Android项目启动了一个新的默认项目.每次我尝试启动应用程序这个错误发生：

的build.gradle(模块：APP)

apply plugin: 'com.android.application'

android {
    compileSdkVersion 21
    buildToolsversion "21.1.2"

    defaultConfig {
        applicationId "com.example.jdevani.validationdemo"
        minSdkVersion 8
        targetSdkVersion 21
        versionCode 1
        versionName "1.0"
    }
    buildTypes {
        release {
            minifyEnabled false
            proguardFiles getDefaultProguardFile('proguard-android.txt'),'proguard-rules.pro'
        }
    }
}

dependencies {
    compile filetree(dir: 'libs',include: ['*.jar'])
    compile 'com.android.support:appcompat-v7:21.0.3'
}

的build.gradle(项目：EmerGencyHelp)

// Top-level build file where you can add configuration options common to all sub-projects/modules.

buildscript {
    repositories {
        jcenter()
    }
    dependencies {
        classpath 'com.android.tools.build:gradle:1.1.0'

        // NOTE: Do not place your application dependencies here; they belong
        // in the individual module build.gradle files
    }
}

allprojects {
    repositories {
        jcenter()
    }
}

我的错误是

information:Gradle tasks [:app:assembleDebug]
:app:preBuild UP-TO-DATE
:app:preDebugBuild UP-TO-DATE
:app:compileDebugNdk UP-TO-DATE
:app:checkDebugManifest
:app:preReleaseBuild UP-TO-DATE
:app:prepareComAndroidSupportAppcompatV72103Library UP-TO-DATE
:app:prepareComAndroidSupportSupportV42103Library UP-TO-DATE
:app:prepareDebugDependencies
:app:compileDebugAidl UP-TO-DATE
:app:compileDebugRenderscript UP-TO-DATE
:app:generateDebugBuildConfig UP-TO-DATE
:app:generateDebugAssets UP-TO-DATE
:app:mergeDebugAssets UP-TO-DATE
:app:generateDebugResValues UP-TO-DATE
:app:generateDebugResources UP-TO-DATE
:app:mergeDebugResources UP-TO-DATE
:app:processDebugManifest UP-TO-DATE
:app:processDebugResources UP-TO-DATE
:app:generateDebugSources UP-TO-DATE
:app:compileDebugJava
Note: C:\Users\vfinava\Desktop\Project\EmerGencyHelp\app\src\main\java\com\example\vfinava\emergencyhelp\DataHelper.java uses unchecked or unsafe operations.
Note: Recompile with -Xlint:unchecked for details.
:app:preDexDebug
:app:dexDebug
UNEXPECTED TOP-LEVEL EXCEPTION:
com.android.dex.DexException: Multiple dex files define Landroid/support/v4/accessibilityservice/AccessibilityServiceInfoCompatIcs;
    at com.android.dx.merge.DexMerger.readSortableTypes(DexMerger.java:596)
    at com.android.dx.merge.DexMerger.getSortedTypes(DexMerger.java:554)
    at com.android.dx.merge.DexMerger.mergeClassDefs(DexMerger.java:535)
    at com.android.dx.merge.DexMerger.mergeDexes(DexMerger.java:171)
    at com.android.dx.merge.DexMerger.merge(DexMerger.java:189)
    at com.android.dx.command.dexer.Main.mergeLibraryDexBuffers(Main.java:454)
    at com.android.dx.command.dexer.Main.runMonoDex(Main.java:303)
    at com.android.dx.command.dexer.Main.run(Main.java:246)
    at com.android.dx.command.dexer.Main.main(Main.java:215)
    at com.android.dx.command.Main.main(Main.java:106)

Error:Execution Failed for task ':app:dexDebug'.
> com.android.ide.common.process.ProcessException: org.gradle.process.internal.ExecException: Process 'command 'C:\Program Files\Java\jdk1.8.0_20\bin\java.exe'' finished with non-zero exit value 2

information:BUILD Failed
information:Total time: 5.684 secs
information:1 error
information:0 warnings
information:See complete output in console

请帮帮我
提前致谢,

解决方法

也许你不要在你的项目中正确添加suport-v4库.
检查这个：

>你将这个库添加到所有需要的模块中(如果有的话)
比您的项目中的模块多,如主模块和库
模块).
检查你不要添加这个库两次.

最后,如果没有解决您的问题,请尝试从导入的库列表和项目模块依赖列表中删除此库,并将其从一个源重新导入到项目中,然后尝试重新构建项目或重新启动IDE.我希望这样可以帮助你:)