无法运行Hello world

Question

我正在关注下载android studio以及如何设置它的课程,我已经为我的手机下载了正确的驱动程序但是当我尝试运行我的hello world程序时我遇到了问题.

请记住,课程本身建议我更新名为activity_main.xml的文件.这是该文件的先前内容:

<?xml version="1.0" encoding="utf-8"?>
<android.support.constraint.ConstraintLayout
xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:app="http://schemas.android.com/apk/res-auto"
xmlns:tools="http://schemas.android.com/tools"
android:id="@+id/activity_main"
android:layout_width="match_parent"
 android:layout_height="match_parent"
 tools:context="com.udacity.myapplication.MainActivity">

<TextView
    android:layout_width="wrap_content"
    android:layout_height="wrap_content"
    android:text="Hello World!"
    app:layout_constraintLeft_toLeftOf="@+id/activity_main"
    app:layout_constraintTop_toTopOf="@+id/activity_main"
    app:layout_constraintRight_toRightOf="@+id/activity_main"
    app:layout_constraintBottom_toBottomOf="@+id/activity_main" />

    </android.support.constraint.ConstraintLayout>

必须更新此代码才能与视频保持一致.新细分:

<?xml version="1.0" encoding="utf-8"?>
<RelativeLayout
xmlns:android="http://schemas.android.com/apk/res/android"
 xmlns:tools="http://schemas.android.com/tools"
 android:layout_width="match_parent"
 android:layout_height="match_parent"
 android:paddingBottom="@dimen/activity_vertical_margin"
 android:paddingLeft="@dimen/activity_horizontal_margin"
 android:paddingRight="@dimen/activity_horizontal_margin"
 android:paddingTop="@dimen/activity_vertical_margin"
 tools:context="com.udacity.myapplication.MainActivity">

<TextView
    android:layout_width="wrap_content"
    android:layout_height="wrap_content"
    android:text="Hello World!" />
  </RelativeLayout>

当我尝试在手机上运行应用程序时,我得到的是:

Error:(7, 28) No resource found that matches the given name (at ‘paddingBottom’ with value ‘@dimen/activity_vertical_margin’).
Error:(8, 26) No resource found that matches the given name (at ‘paddingLeft’ with value ‘@dimen/activity_horizontal_margin’).
Error:(9, 27) No resource found that matches the given name (at ‘paddingRight’ with value ‘@dimen/activity_horizontal_margin’).
Error:(10, 25) No resource found that matches the given name (at ‘paddingTop’ with value ‘@dimen/activity_vertical_margin’).
Error:Execution failed for task ‘:app:processDebugResources’.

有帮助吗？

Answer 1

从RelativeLayout中删除这些行:

 android:paddingBottom="@dimen/activity_vertical_margin"
 android:paddingLeft="@dimen/activity_horizontal_margin"
 android:paddingRight="@dimen/activity_horizontal_margin"
 android:paddingTop="@dimen/activity_vertical_margin"

或者更改值:

 android:paddingBottom="16dp"
 android:paddingLeft="16dp"
 android:paddingRight="16dp"
 android:paddingTop="16dp"

@dimen/...是对res/values/dimens.xml文件中的维度值的引用.你可能没有任何值,这就是你得到这个错误的原因.