Gradle failed to resolve library in Android Studio

I want to include a library in Android Studio , but it displays error like below :

"Failed to resolve:com.lemonlab:expandable-button-menu:1.0.0"

How to fix this problem?

    apply plugin: 'com.android.application'

    android {
        compileSdkVersion 21
        buildToolsVersion '21.1.2'

        defaultConfig {
            applicationId "ayowes.com.newecampus"
            minSdkVersion 15
            targetSdkVersion 21
            versionCode 1
            versionName "1.0"
        }
        buildTypes {
            release {
                minifyEnabled false
                proguardFiles getDefaultProguardFile('proguard-android-ptimize.txt'), 'proguard-rules.txt'
            }
        }
    }

    dependencies {
        compile fileTree(dir: 'libs', include: ['*.jar'])
        compile 'com.android.support:appcompat-v7:21.0.3'
        compile 'com.google.android.gms:play-services:6.5.87'
        compile 'com.lemonlab:expandable-button-menu:1.0.0'
        compile files('libs/pinchzoom.jar')
    }

You go File->Settings->Gradle Look at the "Offline work" inbox, if it's checked u uncheck and try to sync again I have the same problem and i try this , the problem resolved. Good luck !

I had the same problem, the first thing that came to mind was repositories. So I checked the build.gradle file for the whole project and added the following code, then synchronized the gradle with project and problem was solved!

allprojects {
    repositories {
        jcenter()
    }
}

Some time you may just need to add maven { url "https://jitpack.io" } in your allprojects block in project level build.gradle file.

Example:

allprojects {
    repositories {
        jcenter()
        maven { url "https://jitpack.io" }
    }
}