Android Cordova构建需要SDK平台

我在Ubuntu上，安装了cordova、cordova cli、android studio和所有软件包，但当我尝试构建我的应用程序时，我收到了以下错误：

Running command: /home/admin/Desktop/hello/platforms/android/cordova/build 
[Error: Please install Android target: "android-21".

Hint: Open the SDK manager by running: /opt/android-sdk/tools/android
You will require:
1. "SDK Platform" for android-21
2. "Android SDK Platform-tools (latest)
3. "Android SDK Build-tools" (latest)]
ERROR building one of the platforms: Error: /home/admin/Desktop/hello/platforms/android/cordova/build: Command failed with exit code 2
You may not have the required environment or OS to build this project
Error: /home/admin/Desktop/hello/platforms/android/cordova/build: Command failed with exit code 2
    at ChildProcess.whenDone (/usr/local/lib/node_modules/cordova/node_modules/cordova-lib/src/cordova/superspawn.js:131:23)
    at ChildProcess.EventEmitter.emit (events.js:98:17)
    at maybeClose (child_process.js:743:16)
    at Process.ChildProcess._handle.onexit (child_process.js:810:5)

注意：我在bashrc中添加了android sdk的路径：

#AndroidDev PATH

export PATH=${PATH}:${HOME}/android-sdk-linux/tools

export PATH=${PATH}:${HOME}/android-sdk-linux/platform-tools

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你的问题是对的

在Android SDK中更新您的

SDK工具

和“SDK构建”工具。使用EclipseADT，它看起来像这样

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安装21软件包，因为您的cordova版本需要21软件包

我不明白，我已经全部安装好了，还有其他建议吗？您是否安装了SDK build tools 21？根据此

请安装Android目标：“Android-21”

它未随SDK一起安装。