小编jub*_*kon的帖子

我在SpringToolSuite中有一个动态Web项目.它被转换为Maven项目.

我遇到了这个问题:

Mising artifact org.springframework:spring.jar:4.2.6

我已经尝试过清理,重建和运行项目.它给:

读取文件C时出错:\ Users\jublikon.m2\repository\org\springframework\spring\4.2.6\spring-4.2.6.jar C:\ Users\jublikon.m2\repository\org\springframework\spring\4.2. 6\spring-4.2.6.jar(系统找不到指定的文件)

我不明白为什么我在使用Maven时要求jar文件？

的pom.xml

    <?xml version="1.0"?>
<project xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd" xmlns="http://maven.apache.org/POM/4.0.0"
    xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance">
  <modelVersion>4.0.0</modelVersion>
  <groupId>HelloWeb</groupId>
  <artifactId>HelloWeb</artifactId>
  <version>0.0.1-SNAPSHOT</version>
  <packaging>war</packaging>
  <dependencies>
    <dependency>
      <groupId>org.springframework</groupId>
      <artifactId>spring-context</artifactId>
      <scope>compile</scope>
    </dependency>
    <dependency>
      <groupId>org.springframework</groupId>
      <artifactId>spring-core</artifactId>
      <scope>compile</scope>
    </dependency>
    <dependency>
      <groupId>org.springframework</groupId>
      <artifactId>spring-web</artifactId>
      <scope>compile</scope>
    </dependency>
    <dependency>
      <groupId>org.springframework</groupId>
      <artifactId>spring-webmvc</artifactId>
      <scope>compile</scope>
    </dependency>
    <dependency>
      <groupId>org.springframework</groupId>
      <artifactId>spring-aspects</artifactId>
      <scope>compile</scope>
    </dependency>
  </dependencies>
  <repositories>
    <repository>
      <snapshots>
        <enabled>false</enabled>
      </snapshots>
      <id>central</id>
      <name>Central Repository</name>
      <url>https://repo.maven.apache.org/maven2</url>
    </repository>
  </repositories>
  <pluginRepositories>
    <pluginRepository>
      <releases>
        <updatePolicy>never</updatePolicy>
      </releases>
      <snapshots>
        <enabled>false</enabled>
      </snapshots>
      <id>central</id>
      <name>Central Repository</name>
      <url>https://repo.maven.apache.org/maven2</url>
    </pluginRepository>
  </pluginRepositories>
  <build>
    <sourceDirectory>C:\Users\name\Development\Spring\Projects\HelloWeb\src\main\java</sourceDirectory>
    <scriptSourceDirectory>C:\Users\name\Development\Spring\Projects\HelloWeb\src\main\scripts</scriptSourceDirectory> …

问题:我正在使用maven并突然遇到一些错误:

For artifact {org.springframework.boot:spring-boot-starter-data-jpa:null:jar}: The version cannot be empty. (org.apache.maven.plugins:maven-resources-plugin:2.6:resources:default-resources:process-resources)

org.apache.maven.artifact.InvalidArtifactRTException: For artifact {org.springframework.boot:spring-boot-starter-data-jpa:null:jar}: The version cannot be empty.
    at org.apache.maven.artifact.DefaultArtifact.validateIdentity(DefaultArtifact.java:148)
    at org.apache.maven.artifact.DefaultArtifact.<init>(DefaultArtifact.java:123)
    at org.apache.maven.artifact.factory.DefaultArtifactFactory.createArtifact(DefaultArtifactFactory.java:157)
    at org.apache.maven.artifact.factory.DefaultArtifactFactory.createDependencyArtifact(DefaultArtifactFactory.java:57)
    at org.apache.maven.project.artifact.MavenMetadataSource.createDependencyArtifact(MavenMetadataSource.java:328)
    at org.apache.maven.project.artifact.MavenMetadataSource.createArtifacts(MavenMetadataSource.java:503)
    at org.apache.maven.lifecycle.internal.DefaultProjectArtifactFactory.createArtifacts(DefaultProjectArtifactFactory.java:50)
    at org.apache.maven.lifecycle.internal.LifecycleDependencyResolver.resolveProjectDependencies(LifecycleDependencyResolver.java:119)
    at org.apache.maven.lifecycle.internal.MojoExecutor.ensureDependenciesAreResolved(MojoExecutor.java:245)
    at org.eclipse.m2e.core.internal.embedder.MavenImpl.execute(MavenImpl.java:330)
    at org.eclipse.m2e.core.internal.embedder.MavenImpl$11.call(MavenImpl.java:1362)
    at org.eclipse.m2e.core.internal.embedder.MavenImpl$11.call(MavenImpl.java:1)
    at org.eclipse.m2e.core.internal.embedder.MavenExecutionContext.executeBare(MavenExecutionContext.java:176)
    at org.eclipse.m2e.core.internal.embedder.MavenExecutionContext.execute(MavenExecutionContext.java:112)
    at org.eclipse.m2e.core.internal.embedder.MavenImpl.execute(MavenImpl.java:1360)
    at org.eclipse.m2e.core.project.configurator.MojoExecutionBuildParticipant.build(MojoExecutionBuildParticipant.java:52)
    at org.eclipse.m2e.core.internal.builder.MavenBuilderImpl.build(MavenBuilderImpl.java:137)
    at org.eclipse.m2e.core.internal.builder.MavenBuilder$1.method(MavenBuilder.java:172)
    at org.eclipse.m2e.core.internal.builder.MavenBuilder$1.method(MavenBuilder.java:1)
    at org.eclipse.m2e.core.internal.builder.MavenBuilder$BuildMethod$1$1.call(MavenBuilder.java:115)
    at org.eclipse.m2e.core.internal.embedder.MavenExecutionContext.executeBare(MavenExecutionContext.java:176)
    at org.eclipse.m2e.core.internal.embedder.MavenExecutionContext.execute(MavenExecutionContext.java:112)
    at org.eclipse.m2e.core.internal.builder.MavenBuilder$BuildMethod$1.call(MavenBuilder.java:105)
    at org.eclipse.m2e.core.internal.embedder.MavenExecutionContext.executeBare(MavenExecutionContext.java:176)
    at org.eclipse.m2e.core.internal.embedder.MavenExecutionContext.execute(MavenExecutionContext.java:151)
    at org.eclipse.m2e.core.internal.embedder.MavenExecutionContext.execute(MavenExecutionContext.java:99)
    at org.eclipse.m2e.core.internal.builder.MavenBuilder$BuildMethod.execute(MavenBuilder.java:86)
    at org.eclipse.m2e.core.internal.builder.MavenBuilder.build(MavenBuilder.java:200)
    at org.eclipse.core.internal.events.BuildManager$2.run(BuildManager.java:735)
    at org.eclipse.core.runtime.SafeRunner.run(SafeRunner.java:42) …

我想以编程方式在ViewPager中制作一张幻灯片。

我的问题是，滑动事件是由放置在ViewPager所保存片段中的按钮调用的。

我知道代码：

viewpager.setCurrentItem(int index)

现在，我的想法是使ViewPager变量成为公共静态变量，以从子片段访问它。但是不能从子片段访问静态变量。

如何通过单击页面内的按钮来实现幻灯片制作？

问题:我有一个RecyclerView和Toolbar一个CoordinatorLayout.在RecyclerView低于Toolbar但它不应该.

问题:我怎样才能实现RecyclerView和Toolbar拥有一个边界？

activity_main.xml中

<?xml version="1.0" encoding="utf-8"?>
<android.support.design.widget.CoordinatorLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    xmlns:app="http://schemas.android.com/apk/res-auto"
    android:fitsSystemWindows="true">

    <android.support.design.widget.AppBarLayout
        android:id="@+id/appBar"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:theme="@style/ThemeOverlay.AppCompat.ActionBar">

    <include
        android:id="@+id/toolbar_main"
        layout="@layout/toolbar"></include>

    </android.support.design.widget.AppBarLayout>

    <FrameLayout
        android:id="@+id/maschinelistcontainer"
        android:layout_width="match_parent"
        android:layout_height="match_parent" />

</android.support.design.widget.CoordinatorLayout>

maschine_fragment.xml

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:orientation="vertical"
    android:layout_width="match_parent"
    android:layout_height="match_parent">

    <android.support.v7.widget.RecyclerView
        android:id="@+id/recycler_view"
        android:layout_width="match_parent"
        android:layout_height="match_parent"
        android:clipToPadding="false"
        android:scrollbars="vertical" />

</LinearLayout>

我有一个ViewPager我想添加片段的。ViewPager 可以在屏幕上正确查看，但不幸的是它不包含任何内容。

我在一些帖子中看到了替换的建议

getSupportFragmentManager() 

和

getChildFragmentManager()

但我需要ActionBar. 不幸的ChildFragmentmanager是，在AppCompatActivity.

在调试时，我意识到 Fragment 的onCreateView()方法被调用并返回一个布局。

问题：我怎样才能使Fragments可见？是我的代码与该示例的主要区别什么？

活动：

public class ViewPagerActivity extends AppCompatActivity {

    private ViewPager mViewPager;

    private List<Location> locationList = new ArrayList<>();
    private locationsBaseHandler db;
    private CustomPagerAdapter mAdapter;

    private Location mLocation;

    @Override
    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);

        setContentView(R.layout.activity_viewpager);

        locationList.add(someData);

        mViewPager = (ViewPager) findViewById(R.id.viewpager);
        mAdapter  = new CustomPagerAdapter(this, getSupportFragmentManager(), locationList);

        mViewPager.setAdapter(mAdapter);

    }

}

寻呼机适配器：

public class …

我有一个collapsingToolbarLayout，我需要对 title 做一些额外的设置TextView。

问题：如何获得对该 TextView 的引用？

<android.support.design.widget.CoordinatorLayout 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/review_coordinator_layout"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:fitsSystemWindows="true"
    tools:context="com.stack.overflow.reviewmaschine.ReviewMaschineActivity"
    tools:ignore="MergeRootFrame">

    <android.support.design.widget.AppBarLayout
        android:id="@+id/app_bar"
        android:layout_width="match_parent"
        android:layout_height="@dimen/app_bar_height"
        android:fitsSystemWindows="true"
        android:theme="@style/ThemeOverlay.AppCompat.Dark.ActionBar">

        <android.support.design.widget.CollapsingToolbarLayout
            android:id="@+id/toolbar_layout"
            android:layout_width="match_parent"
            android:layout_height="match_parent"
            android:fitsSystemWindows="true"
            app:contentScrim="?attr/colorPrimary"
            app:layout_scrollFlags="scroll|exitUntilCollapsed"
            app:toolbarId="@+id/toolbar">

            <android.support.v7.widget.Toolbar
                android:id="@+id/detail_toolbar"
                android:layout_width="match_parent"
                android:layout_height="?attr/actionBarSize"
                app:layout_collapseMode="pin"
                app:popupTheme="@style/ThemeOverlay.AppCompat.Light" />

        </android.support.design.widget.CollapsingToolbarLayout>

    </android.support.design.widget.AppBarLayout>

    <FrameLayout
        android:id="@+id/item_detail_container"
        android:layout_width="match_parent"
        android:layout_height="match_parent"
        app:layout_behavior = "@string/appbar_scrolling_view_behavior"
        />

    <com.mego.smscloud.reviewmaschine.SaveFloatingActionButton
        android:id="@+id/review_fab"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_gravity="bottom|end"
        android:backgroundTint="@color/colorPrimary"
        android:layout_margin="@dimen/fab_margin"
        android:src="@drawable/ic_floppy_white_48dp"
        app:borderWidth="0dp"
        app:elevation="@dimen/fab_elevation"
        app:rippleColor="#00ffff"/>

</android.support.design.widget.CoordinatorLayout>

编辑： 简单地将 a 添加TextView到 theToolbar并不能将其集成到与CollapsingToolbarLayouttitle相同的行为中

我有一个tree由数据结构表示:

data Tree a = Node (Tree a) (Tree a)| Leaf a

t1 :: Tree Int
t1 = (Node (Node (Leaf 23) (Leaf 42)) (Node (Leaf 19) (Leaf 65)))

现在我需要打印叶子的数据:

toList :: Tree a -> [a]
toList (Node (Leaf a) (Leaf b))       = [a] ++ [b]
toList (Node (Leaf a) (Node x y))     = [a] ++ (toList (Node x y))
toList (Node (Node x y) (Leaf b))     = (toList (Node x y)) ++ [b]

不幸的是,我一直收到错误:

函数toList中的非穷举模式

但是我使用括号.

我做错了什么？

我只是想扩展ImageView:

import android.content.Context;
import android.util.AttributeSet;
import android.widget.ImageView;

public class SquareImageView extends ImageView {

    public SquareImageView(Context context) {
        super(context);
    }

    public SquareImageView(Context context, AttributeSet attrs) {
        super(context, attrs);
    }

    public SquareImageView(Context context, AttributeSet attrs, int defStyleAttr) {
        super(context, attrs, defStyleAttr);
    }

    @Override
    protected void onMeasure(int widthMeasureSpec, int heightMeasureSpec) {
        super.onMeasure(widthMeasureSpec, heightMeasureSpec);

        int width = getMeasuredWidth();
        setMeasuredDimension(width, width);
    }

}

但是Android Studio会返回编译错误:

此自定义视图应该扩展android.support.v7.widget.AppCompatImageView

但导入android.support.v7.widget.AppCompatImageViewinsted android.widget.ImageView并不能解决问题,因为ImageView被标记为未导入...

我在这做错了什么？

当我将屏幕方向从垂直更改为水平然后再次返回时，RecyclerView 会重新绘制并覆盖旧的（您可以在卡片视图之间看到它）：

问题：如何抑制这种行为，以便 Android 始终重用最初创建的 RecyclerView？

XML 片段

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:app="http://schemas.android.com/apk/res-auto"
    xmlns:lib="http://schemas.android.com/tools"
    android:id="@+id/maschine_fragment"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:orientation="vertical">

    <android.support.v7.widget.RecyclerView
        android:id="@+id/maschine_recycler_view"
        android:layout_width="match_parent"
        android:layout_height="match_parent"
        android:clipToPadding="false"
        android:scrollbars="vertical"
        app:layout_behavior="@string/appbar_scrolling_view_behavior" />

</LinearLayout>

主要XML

<?xml version="1.0" encoding="utf-8"?>
<android.support.design.widget.CoordinatorLayout
    android:id="@+id/maschineCoordinatorLayout"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    xmlns:app="http://schemas.android.com/apk/res-auto"
    android:fitsSystemWindows="true"
    xmlns:android="http://schemas.android.com/apk/res/android">

    <android.support.design.widget.AppBarLayout
        android:id="@+id/appBar"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:theme="@style/ThemeOverlay.AppCompat.ActionBar">

        <include
            android:id="@+id/toolbar_main"
            layout="@layout/toolbar"></include>

    </android.support.design.widget.AppBarLayout>

    <FrameLayout
    android:id="@+id/machinelistcontainer"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    app:layout_behavior = "@string/appbar_scrolling_view_behavior"
    />

    <android.support.design.widget.FloatingActionButton
        android:id="@+id/fab_cloud_sync_maschinen"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_gravity="bottom|end"
        android:layout_margin="@dimen/fab_margin"
        android:backgroundTint="@color/colorPrimary"
        android:src="@drawable/ic_cloud_sync_white_48dp"
        app:borderWidth="0dp"
        app:elevation="@dimen/fab_elevation"
        app:rippleColor="#00ffff"/>

</android.support.design.widget.CoordinatorLayout>

我有两节课A和B。

问题：为什么该行System.out.println(b.x)结果打印 23？

我同意结果为 22，因为 的构造函数A和 每个构造函数都会将 1B递增static int y。

public class A {
   public long x = 0;
   public static int y = 20;

   public A(float x) {
      this((int) x );
      A.y++;
   }

   public A(int x) {
      this.x = x;
   }

   public int f(double d) {
      return 1;
   }

   public int f(long l) {
      return 2;
   }
}

public class B extends A {
   public int …