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.