Android Launcher 3 简单分析

最近在学习Android Launcher的相关知识，在github上找到可以在Android studio上编译的Launcher 3代码，地址：https://github.com/rydanliu/Launcher3

Launcher 3的界面主要由SearchDropTargetBar、Workspace、CellLayout、PageIndicator、Hotseat组成。如下图：

Launcher 3 最主要的是一个Activity，基本上所有操作都集中在这个Activity上。这个Activity文件为Launcher.java，他的布局文件为launcher.xml。

下面为竖屏的布局文件，路径为res/layout-port/launcher.xml。

 <?xml version="1.0" encoding="utf-8"?>

 <!-- Full screen view projects under the status bar and contains the background -->
 <com.android.launcher3.LauncherRootView xmlns:android="http://schemas.android.com/apk/res/android"
     xmlns:launcher="http://schemas.android.com/apk/res-auto"
     android:id="@+id/launcher"
     android:layout_width="match_parent"
     android:layout_height="match_parent"
     android:fitsSystemWindows="true">

     <com.android.launcher3.DragLayer
         android:id="@+id/drag_layer"

         android:layout_width="match_parent"
         android:layout_height="match_parent">

         <com.android.launcher3.FocusIndicatorView
             android:id="@+id/focus_indicator"
             android:layout_width="22dp"
             android:layout_height="22dp" />

         <!-- The workspace contains 5 screens of cells -->
         <!-- DO NOT CHANGE THE ID -->
         <com.android.launcher3.Workspace
             android:id="@+id/workspace"
             android:layout_width="match_parent"
             android:layout_height="match_parent"
             launcher:defaultScreen="@integer/config_workspaceDefaultScreen"
             launcher:pageIndicator="@+id/page_indicator"></com.android.launcher3.Workspace>

         <!-- DO NOT CHANGE THE ID -->
         <include
             android:id="@+id/hotseat"
             layout="@layout/hotseat"

             android:layout_width="match_parent"
             android:layout_height="match_parent" />

         <include
             android:id="@+id/overview_panel"
             layout="@layout/overview_panel"
             android:visibility="gone" />

         <!-- Keep these behind the workspace so that they are not visible when
              we go into AllApps -->
         <include
             android:id="@+id/page_indicator"
             layout="@layout/page_indicator"
             android:layout_width="wrap_content"
             android:layout_height="wrap_content"
             android:layout_gravity="center_horizontal" />

         <include
             android:id="@+id/search_drop_target_bar"

             layout="@layout/search_drop_target_bar" />

         <include
             android:id="@+id/widgets_view"
             layout="@layout/widgets_view"
             android:layout_width="match_parent"
             android:layout_height="match_parent"
             android:visibility="invisible" />

         <include
             android:id="@+id/apps_view"
             layout="@layout/all_apps"
             android:layout_width="match_parent"
             android:layout_height="match_parent"
             android:visibility="invisible" />
     </com.android.launcher3.DragLayer>

     <ViewStub
         android:id="@+id/launcher_overlay_stub"
         android:layout_width="match_parent"
         android:layout_height="match_parent"
         android:inflatedId="@+id/launcher_overlay"
         android:layout="@layout/launcher_overlay" />
 </com.android.launcher3.LauncherRootView>

SearchDropTargetBar

屏幕最上方有个搜索框，在我们拖动图标的时候，搜索框会替换成“删除“

Workspace

就是屏幕上左右滑的好几屏幕的容器

CellLayout

Workspace里面可以滑动的单独一屏，CellLayout负责图标和小部件的显示和整齐摆放。

PageIndicator

滑动屏幕的时候看见下方的指示器

Hotseat

用来放置比较常用的应用，比如拨号，短信，相机等。

下面介绍几个类

CellLayout 类

mCountX 和 mCountY   分别表示 “x方向icon的个数” 和 “y方向icon的个数”

mOccupied 二维数组用来标记每个cell是否被占用，内部类CellInfo为静态类，其对象用于存储cell的基本信息。

DeviceProfile 类

设置各元素布局的padding  。修改workspace的padding使用getWorkspacePadding方法。

     /** Returns the workspace padding in the specified orientation */
     Rect getWorkspacePadding(boolean isLayoutRtl) {
         Rect searchBarBounds = getSearchBarBounds(isLayoutRtl);
         Rect padding = new Rect();
         if (isLandscape && transposeLayoutWithOrientation) {
             // Pad the left and right of the workspace with search/hotseat bar sizes
             if (isLayoutRtl) {
                 padding.set(hotseatBarHeightPx, edgeMarginPx,
                         searchBarBounds.width(), edgeMarginPx);
             } else {
                 padding.set(searchBarBounds.width(), edgeMarginPx,
                         hotseatBarHeightPx, edgeMarginPx);
             }
         } else {
             if (isTablet) {
                 // Pad the left and right of the workspace to ensure consistent spacing
                 // between all icons
                 float gapScale = 1f + (dragViewScale - 1f) / 2f;
                 int width = getCurrentWidth();
                 int height = getCurrentHeight();
                 int paddingTop = searchBarBounds.bottom;
                 int paddingBottom = hotseatBarHeightPx + pageIndicatorHeightPx;
                 int availableWidth = Math.max(0, width - (int) ((inv.numColumns * cellWidthPx) +
                         (inv.numColumns * gapScale * cellWidthPx)));
                 int availableHeight = Math.max(0, height - paddingTop - paddingBottom
                         - (int) (2 * inv.numRows * cellHeightPx));
                 padding.set(availableWidth / 2, paddingTop + availableHeight / 2,
                         availableWidth / 2, paddingBottom + availableHeight / 2);
             } else {
                 // Pad the top and bottom of the workspace with search/hotseat bar sizes

                 padding.set(desiredWorkspaceLeftRightMarginPx - defaultWidgetPadding.left,
                         searchBarBounds.bottom,
                         desiredWorkspaceLeftRightMarginPx - defaultWidgetPadding.right,
                         hotseatBarHeightPx + pageIndicatorHeightPx);

             }
         }
         return padding;
     }

比如我要将workspace里图标顶部不留空隙，需要设置padding.set的第二个参数为0.

 padding.set(desiredWorkspaceLeftRightMarginPx - defaultWidgetPadding.left,
                         0,//searchBarBounds.bottom,
                         desiredWorkspaceLeftRightMarginPx - defaultWidgetPadding.right,
                         hotseatBarHeightPx + pageIndicatorHeightPx);

InvariantDeviceProfile类

一些不变的设备相关参数管理类，landscapeProfile 和 portraitProfile为横竖屏模式的DeviceProfile。

getPredefinedDeviceProfiles方法 负责加载在不同设备上不同的布局，和图标大小等。

 ArrayList<InvariantDeviceProfile> getPredefinedDeviceProfiles() {
         ArrayList<InvariantDeviceProfile> predefinedDeviceProfiles = new ArrayList<>();
         // width, height, #rows, #columns, #folder rows, #folder columns,
         // iconSize, iconTextSize, #hotseat, #hotseatIconSize, defaultLayoutId.
         predefinedDeviceProfiles.add(new InvariantDeviceProfile("Super Short Stubby",
                 255, 300,     2, 3, 2, 3, 3, 48, 13, 3, 48, R.xml.default_workspace_4x4));
         predefinedDeviceProfiles.add(new InvariantDeviceProfile("Shorter Stubby",
                 255, 400,     3, 3, 3, 3, 3, 48, 13, 3, 48, R.xml.default_workspace_4x4));
         predefinedDeviceProfiles.add(new InvariantDeviceProfile("Short Stubby",
                 275, 420,     3, 4, 3, 4, 4, 48, 13, 5, 48, R.xml.default_workspace_4x4));
         predefinedDeviceProfiles.add(new InvariantDeviceProfile("Stubby",
                 255, 450,     3, 4, 3, 4, 4, 48, 13, 5, 48, R.xml.default_workspace_4x4));
         predefinedDeviceProfiles.add(new InvariantDeviceProfile("Nexus S",
                 296, 491.33f, 4, 4, 4, 4, 4, 48, 13, 5, 48, R.xml.default_workspace_4x4));
         predefinedDeviceProfiles.add(new InvariantDeviceProfile("Nexus 4",
                 335, 567,     4, 4, 4, 4, 4, DEFAULT_ICON_SIZE_DP, 13, 5, 56, R.xml.default_workspace_4x4));

         predefinedDeviceProfiles.add(new InvariantDeviceProfile("Nexus 5",
                 359, 567,     4, 4, 4, 4, 4, DEFAULT_ICON_SIZE_DP, 13, 5, 56, R.xml.default_workspace_4x4));
         predefinedDeviceProfiles.add(new InvariantDeviceProfile("Large Phone",
                 406, 694,     5, 5, 4, 4, 4, 64, 14.4f,  5, 56, R.xml.default_workspace_5x5));
         // The tablet profile is odd in that the landscape orientation
         // also includes the nav bar on the side
         predefinedDeviceProfiles.add(new InvariantDeviceProfile("Nexus 7",
                 575, 904,     5, 6, 4, 5, 4, 72, 14.4f,  7, 60, R.xml.default_workspace_5x6));
         // Larger tablet profiles always have system bars on the top & bottom
         predefinedDeviceProfiles.add(new InvariantDeviceProfile("Nexus 10",
                 727, 1207,    5, 6, 4, 5, 4, 76, 14.4f,  7, 64, R.xml.default_workspace_5x6));
         predefinedDeviceProfiles.add(new InvariantDeviceProfile("20-inch Tablet",
                 1527, 2527,   7, 7, 6, 6, 4, 100, 20,  7, 72, R.xml.default_workspace_4x4));
         return predefinedDeviceProfiles;
     }

比如我在上面代码的17行加入下列代码，将Hotseat设置成3格，图标大小为72dp

         predefinedDeviceProfiles.add(new InvariantDeviceProfile("MX 4",
                 359, 567,     4, 4, 4, 4, 4, DEFAULT_ICON_SIZE_DP, 13, , , R.xml.default_workspace_4x4));

由于launcher是有许多自定义控件构成的，这里涉及到onMesure,onLayout,onDraw方法的复写

onMesure方法顾名思义,主要是用来重新测量自定义控件的高度和宽度,就是设置它的dimesion,一般所有自定义VIEW都需要复写这个方法。

onLayout则主要是ViewGroup需要复写这个方法,其作用给这个ViewGroup下子View布局好显示的位置。

onDraw则是需要真真正正画出内容的控件需要复写的方法,比如textview,或者其子类,其最终利用一个很重要的类Canvas的对象来实现一系列的画图,比如canvas.drawcircle,canvas.drawline.