我正在尝试弄清楚如何在我的 Android 应用程序( Material 设计)工具栏中创建面包屑。

这可以在最新的 Dropbox android 应用程序中看到，其中面包屑用于显示文件的导航。

我还找到了一张图片(我从 another similar question 中截取的)，可以在这里看到:

你能指导我如何做到这一点吗？

最佳答案

我为一个应用程序创建了一个这样的工作示例，我想我会分享，因为它变得比它需要的更困惑，哈哈。也许它可以为一些开发人员节省很多本不应该需要的工作:)

将 Horizo​​ntalScrollView 添加到您的 AppBarLayout(layout/examplebreadcrumbs_layout)

<android.support.v7.widget.AppBarLayout
        android:id="@+id/app_bar"
        style="@style/HeaderBar"
        android:layout_width="match_parent"
        android:layout_height="wrap_content">

    <android.support.v7.widget.Toolbar
        android:id="@+id/toolbar"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:background="?colorPrimary"
        android:minHeight="?attr/actionBarSize"
        app:contentInsetStart="72dp"
        app:navigationContentDescription="up" />

    <HorizontalScrollView android:id="@+id/breadcrumb_wrapper"
        android:layout_width="match_parent"
        android:layout_height="50dp"
        android:scrollbars="none">

        <LinearLayout android:id="@+id/breadcrumbs"
            android:orientation="horizontal"
            android:layout_width="wrap_content"
            android:layout_height="match_parent"
            android:layout_gravity="center_vertical"
            android:gravity="center_vertical"
            android:paddingEnd="@dimen/activity_horizontal_margin_2"
            android:paddingStart="@dimen/activity_horizontal_margin_2"/>

    </HorizontalScrollView>

</android.support.v7.widget.AppBarLayout>

创建一个 LinearLayout 将用于每个“面包屑”。您将为每个布局填充相同的布局。 (布局/面包屑文本)

<LinearLayout android:id="@+id/crumb"
    xmlns:tools="http://schemas.android.com/tools"
    xmlns:android="http://schemas.android.com/apk/res/android"
    android:orientation="horizontal"
    android:layout_width="wrap_content"
    android:layout_height="match_parent">

    <TextView
        android:id="@+id/crumb_arrow"
        android:layout_width="wrap_content"
        android:layout_height="match_parent"
        android:visibility="gone"
        android:gravity="center_vertical"
        android:text="@string/greater_than"
        android:padding="4dp"
        android:fontFamily="sans-serif-condensed"
        android:textSize="20sp"
        android:textColor="@color/breadcrumb_text_dim"
        android:textAllCaps="true"
        tools:visibility="visible"/>

    <TextView
        android:id="@+id/crumb_text"
        android:layout_width="wrap_content"
        android:layout_height="match_parent"
        android:padding="4dp"
        android:gravity="center_vertical"
        android:visibility="gone"
        android:fontFamily="sans-serif"
        android:textAllCaps="true"
        android:textSize="14sp"
        android:textColor="@color/breadcrumb_text"
        android:background="?selectableItemBackground"/>

</LinearLayout>

ExampleBreadcrumbs，它演示了基本的创建/更新/滚动方法，您可以轻松地将这些方法添加到您的应用程序流程中。不是 100% 复制粘贴，因为您的应用会有所不同，具体取决于您的面包屑将添加到的 Activity 和设置。如果您需要其他任何东西来让这个工作...让我知道。

public class ExampleBreadcrumbs extends AppCompatActivity {

  private static final String ROOT_NODE = "root";

  private SparseArray<Long> levelNodeIds = new SparseArray<>();
  private SparseArray<String> levelNodeNames = new SparseArray<>();

  public int currentLevel = 0;

  ViewGroup breadcrumbBar;
  HorizontalScrollView breadcrumbWrapper;

  String[] parents = new String[] {"Parent Item 1", "Parent Item 2",
      "Parent Item 3", "Parent Item 4"};

  @Override protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.examplebreadcrumbs_layout);

    breadcrumbWrapper = ((HorizontalScrollView)findViewById(R.id.breadcrumb_wrapper));
    breadcrumbBar = (ViewGroup) findViewById(R.id.breadcrumbs);

    // TODO setup your adapter or whatever

    createParentNodes();
  }

  @Override public void onBackPressed() {
    switch (currentLevel) {
      case 0:
        super.onBackPressed();
        break;
      case 1:
        createParentNodes();
        adapter.notifyDataSetChanged();
        break;
      default:
        // Get values from level you are requesting, not current.
        final long id = levelNodeIds.get(currentLevel - 1);
        final String name = levelNodeNames.get(currentLevel - 1);
        getChildren(id, name, -1);
        break;
    }

  }

  @Override public void onItemClick(View itemView, final String name) {
    long nodeId = (Long) itemView.getTag();
    getChildren(nodeId, name, 1);
  }

  private void getChildren(final long nodeId, final String name, final int difference) {
    if (nodeId != 0) {
      // Example case using retrofit like setup
      getChildren(nodeId, new Callback<NodesResponse>() {
        @Override
        public void onResponse(Call<NodesResponse> call, Response<NodesResponse> response) {
          if (response.body() != null) {
            if (response.body().getNodeObjs() != null && !response.body().getNodeObjs()
                .isEmpty()) {
              createChildNodes(nodeId, name, response.body().getNodeObjs(), difference);
            }
          }
        }

        @Override
        public void onFailure(Call<NodesResponse> call, Throwable t) { // TODO}
      });
    } else {
      createParentNodes();
      adapter.notifyDataSetChanged();
    }
  }

  private void createParentNodes() {
    currentLevel = 0;
    levelNodeIds.put(currentLevel, 0L);
    levelNodeNames.put(currentLevel, ROOT_NODE);

    listItems.clear();
    int count = 0;
    for(String parent : parents) {
      listItems.add(new NodeObj(nodeId[count], parent, parentDescriptions[count]));
      count++;
    }
    adapter.notifyDataSetChanged();
    levelNodeNames.put(currentLevel, ROOT_NODE);
    updateBreadcrumbs(true);
  }

  private void createChildNodes(long id, String name, List<NodeObj> NodeObjs, int difference) {
    listItems.clear();
    for (NodeObj obj : NodeObjs) {
      listItems.add(new NodeObj(obj.getnodeId(), obj.getNodeTitle(), obj.getNodeDescription()));
    }
    adapter.notifyDataSetChanged();

    currentLevel = currentLevel + difference;
    levelNodeIds.put(currentLevel, id);
    levelNodeNames.put(currentLevel, name);

    // If forward, it will create new node along with updating other nodes.
    updateBreadcrumbs(difference > 0);
  }

  private void updateBreadcrumbs(boolean createNew) {
    if (createNew) {
      createBreadcrumb();
    }
    // Loops and updates all breadcrumb nodes
    updateBreadcrumbNodes();
    //printDebug();
  }

  private void createBreadcrumb() {
    boolean needToCreate = true;

    // Remove view if one exists.
    ViewGroup nodeToReplace = (ViewGroup) breadcrumbBar.getChildAt(currentLevel);
    if (nodeToReplace != null) {
      TextView toReplaceTextView = (TextView) nodeToReplace.findViewById(R.id.crumb_text);
      // If node history is not the same, remove view and after.
      if (toReplaceTextView.getText().equals(levelNodeNames.get(currentLevel))) {
        needToCreate = false;
        scrollIfBreadcrumbNotViewable(nodeToReplace);
      } else {
        needToCreate = true;
        // Removes all nodes >= current level
        for (int i = breadcrumbBar.getChildCount() - 1; i >= currentLevel; i--) {
          breadcrumbBar.removeViewAt(i);
        }
      }
    }

    if (needToCreate) {
      // Inflate new breadcrumb node.
      final ViewGroup crumbLayout = (ViewGroup) LayoutInflater.from(this)
          .inflate(R.layout.breadcrumb_text, appBarLayout, false);
      crumbLayout.setTag(levelNodeIds.get(currentLevel));
      // Sets name of node (color gets updated in 'updateBreadcrumbNodes').
      TextView crumbTextView = (TextView) crumbLayout.findViewById(R.id.crumb_text);
      crumbTextView.setVisibility(View.VISIBLE);
      crumbTextView.setText(levelNodeNames.get(currentLevel));
      View crumbArrow = crumbLayout.findViewById(R.id.crumb_arrow);
      crumbArrow.setVisibility(levelNodeNames.get(currentLevel).equals(ROOT_NODE) ? View.GONE : View.VISIBLE);
      // Add new breadcrumb node to bar.
      breadcrumbBar.addView(crumbLayout, currentLevel);
      scrollIfBreadcrumbNotViewable(crumbLayout);
      // Create click listener to jump to history.
      crumbLayout.setOnClickListener(new View.OnClickListener() {
        @Override public void onClick(View v) {
          int viewIndex = breadcrumbBar.indexOfChild(v);
          if (viewIndex == currentLevel) return;
          TextView crumbText = (TextView) v.findViewById(R.id.crumb_text);
          int index = levelNodeNames.indexOfValue(crumbText.getText().toString());
          long nodeId = (Long) v.getTag();
          getChildren(nodeId, levelNodeNames.get(index), viewIndex - currentLevel);
        }
      });
    }

  }

  private void updateBreadcrumbNodes() {
    for (int i = 0; i < breadcrumbBar.getChildCount(); i++) {
      boolean activeNode = i == (currentLevel);
      ViewGroup node = (ViewGroup) breadcrumbBar.getChildAt(i);
      TextView crumbTextView = ((TextView) node.findViewById(R.id.crumb_text));
      crumbTextView.setTextColor(activeNode ? ContextCompat.getColor(this, R.color.breadcrumb_text) :
                                 ContextCompat.getColor(this, R.color.breadcrumb_text_dim));
    }
    breadcrumbWrapper.fullScroll(HorizontalScrollView.FOCUS_BACKWARD);
  }

  private void scrollIfBreadcrumbNotViewable(final ViewGroup view) {
    Rect scrollBounds = new Rect();
    toolbar.getHitRect(scrollBounds);
    if (!view.getLocalVisibleRect(scrollBounds) || scrollBounds.width() < view.getWidth()) {
      view.postDelayed(new Runnable() {
        public void run() {
          breadcrumbWrapper.smoothScrollTo(view.getLeft(), 0);
        }
      }, 100L);
    }
  }

  void printDebug() {
    System.out.println("** DEBUG ** | level: '" + currentLevel + "' | node: id='" + levelNodeIds.get(currentLevel) + "' name='" + levelNodeNames.get(currentLevel) + "' |");
  }
}

关于Android Material 设计 - 如何在工具栏中放置面包屑(导航)？，我们在Stack Overflow上找到一个类似的问题： https://stackoverflow.com/questions/31161333/