Launcher3 一键改变Icon Shape 原理浅析

# Launcher3 一键改变Icon Shape 原理浅析

在Android O Launcher3 Google 团队增加了一个新特性，可以在设置里面更改 桌面Icon 形状，分别可以改为系统默认、方形、方圆形、圆形、泪珠形。
在Android P Launcher3 Google团队继续保持这一神奇特性，那么，看上去好高大上神奇的特性是怎样实现的呢？带着这个疑问，follow me》》》》》

1.png

下面我们基于Android P Launcher3 分析Launcher3 实现基本原理。

一.先看桌面设置中的菜单实现：

源码位置 Launcher90\src\com\android\launcher3\SettingsActivity.java

Preference iconShapeOverride = findPreference(IconShapeOverride.KEY_PREFERENCE);
        if (iconShapeOverride != null) {
            if (IconShapeOverride.isSupported(getActivity())) {
                IconShapeOverride.handlePreferenceUi((ListPreference) iconShapeOverride);
            } else {
                getPreferenceScreen().removePreference(iconShapeOverride);
            }
        }

可以看到isSupported方法是是否支持设置图标形状的判断条件。

public static boolean isSupported(Context context) {

    if (!Utilities.ATLEAST_OREO) {
        return false;
    }
    // Only supported when developer settings is enabled
    if (Settings.Global.getInt(context.getContentResolver(),
            Settings.Global.DEVELOPMENT_SETTINGS_ENABLED, 0) != 1) {
        return false;
    }

    try {
        if (getSystemResField().get(null) != Resources.getSystem()) {
            // Our assumption that mSystem is the system resource is not true.
            return false;
        }
    } catch (Exception e) {
        // Ignore, not supported
        return false;
    }

    return getConfigResId() != 0;
}

由源码 可以看出 满足几个条件才能看到设置选项

1.判断系统SDK 版本是否>=26

2.是否打开了开发者选项。如果开发者选项没打开，就看不到这个菜单。（至于为神马开发者模式才可以看到待追踪！！！可能让厂商在适配此特性吧）

3.大概意思就是获取不到mSystem，如果获取不到，说明当前系统存在问题。

二.菜单出现后，我们选择其中一种形状来设置：

<string-array translatable="false" name="icon_shape_override_paths_values">
    <item></item>
    <item>M50,0L100,0 100,100 0,100 0,0z</item>
    <item>M50,0 C10,0 0,10 0,50 0,90 10,100 50,100 90,100 100,90 100,50 100,10 90,0 50,0 Z</item>
    <item>M50 0A50 50,0,1,1,50 100A50 50,0,1,1,50 0</item>
    <item>M50,0A50,50,0,0 1 100,50 L100,85 A15,15,0,0 1 85,100 L50,100 A50,50,0,0 1 50,0z</item>
</string-array>

<string-array translatable="false" name="icon_shape_override_paths_names">
    <!-- Option to not change the icon shape on home screen. [CHAR LIMIT=50] -->
    <item>@string/icon_shape_system_default</item>
    <item>Square</item>
    <item>Squircle</item>
    <item>Circle</item>
    <item>Teardrop</item>
</string-array>

发现每个Item对应一个path 矢量图的string值。

private static class PreferenceChangeHandler implements OnPreferenceChangeListener {

    private final Context mContext;

    private PreferenceChangeHandler(Context context) {
        mContext = context;
    }

    @Override
    public boolean onPreferenceChange(Preference preference, Object o) {
        String newValue = (String) o;
        if (!getAppliedValue(mContext).equals(newValue)) {
            // Value has changed
            ProgressDialog.show(mContext,
                    null /* title */,
                    mContext.getString(R.string.icon_shape_override_progress),
                    true /* indeterminate */,
                    false /* cancelable */);
            new LooperExecuter(LauncherModel.getWorkerLooper()).execute(
                    new OverrideApplyHandler(mContext, newValue));
        }
        return false;
    }
}

private static class OverrideApplyHandler implements Runnable {

    private final Context mContext;
    private final String mValue;

    private OverrideApplyHandler(Context context, String value) {
        mContext = context;
        mValue = value;
    }

    @Override
    public void run() {
        // Synchronously write the preference.
        prefs(mContext).edit().putString(KEY_PREFERENCE, mValue).commit();
        // Clear the icon cache.
        LauncherAppState.getInstance(mContext).getIconCache().clear();

        // Wait for it
        try {
            Thread.sleep(PROCESS_KILL_DELAY_MS);
        } catch (Exception e) {
            Log.e(TAG, "Error waiting", e);
        }

        // Schedule an alarm before we kill ourself.
        Intent homeIntent = new Intent(Intent.ACTION_MAIN)
                .addCategory(Intent.CATEGORY_HOME)
                .setPackage(mContext.getPackageName())
                .addFlags(Intent.FLAG_ACTIVITY_NEW_TASK);
        PendingIntent pi = PendingIntent.getActivity(mContext, RESTART_REQUEST_CODE,
                homeIntent, PendingIntent.FLAG_CANCEL_CURRENT | PendingIntent.FLAG_ONE_SHOT);
        mContext.getSystemService(AlarmManager.class).setExact(
                AlarmManager.ELAPSED_REALTIME, SystemClock.elapsedRealtime() + 50, pi);

        // Kill process
        android.os.Process.killProcess(android.os.Process.myPid());
    }
}

设置的时候执行上面代码，主要将设置的保存到本地，清除图标缓存，然后kill Launcher process 重启launcher。

三.怎样通过矢量图工作的：

源码位置 ：Launcher90\src\com\android\launcher3\graphics\IconShapeOverride.java

IconShapeOverride.apply(getContext());

private static int getConfigResId() {

    return Resources.getSystem().getIdentifier("config_icon_mask", "string", "android");
}

public static void apply(Context context) {

    if (!Utilities.isAtLeastO()) {
        return;
    }
    String path = getAppliedValue(context);
    if (TextUtils.isEmpty(path)) {
        return;
    }
    if (!isSupported(context)) {
        return;
    }

    // magic
    try {
        Resources override =
                new ResourcesOverride(Resources.getSystem(), getConfigResId(), path);
        getSystemResField().set(null, override);
    } catch (Exception e) {
        Log.e(TAG, "Unable to override icon shape", e);
        // revert value.
        prefs(context).edit().remove(KEY_PREFERENCE).apply();
    }
}

其中ResourcesOverride是继承了Resources，并且重写了getString方法。

private static class ResourcesOverride extends Resources {

    private final int mOverrideId;
    private final String mOverrideValue;

    @SuppressWarnings("deprecated")
    public ResourcesOverride(Resources parent, int overrideId, String overrideValue) {
        super(parent.getAssets(), parent.getDisplayMetrics(), parent.getConfiguration());
        mOverrideId = overrideId;
        mOverrideValue = overrideValue;
    }

    @NonNull
    @Override
    public String getString(int id) throws NotFoundException {
        if (id == mOverrideId) {
            return mOverrideValue;
        }
        return super.getString(id);
    }
}

在根据源码看下getSystemResField方法：

private static Field getSystemResField() throws Exception {
Field staticField = Resources.class.getDeclaredField("mSystem");
staticField.setAccessible(true);
return staticField;
}

这个方法是反射系统Resources中mSystem变量。

小结：

从Launcher 源代码可以看出大概的意思就是Launcher中将Resources 的mSystem设置成了ResourcesOverride对象，
也就是说Resources的getSystem方法获取的是我们重写的ResourcesOverride，当调用getString方法的时候，走的也是重写的方法。getString方法里面判断了如果string id 是config_icon_mask这个的时候，返回我们传入的mOverrideValue，这个mOverrideValue就是用户选择的图标形状值。

2.pmg.jpg

追踪下 AdaptiveIconDrawable的构造方法：

/**
* The one constructor to rule them all. This is called by all public
* constructors to set the state and initialize local properties.
*/

AdaptiveIconDrawable(@Nullable LayerState state, @Nullable Resources res) {
    mLayerState = createConstantState(state, res);

    if (sMask == null) {
        sMask = PathParser.createPathFromPathData(
            Resources.getSystem().getString(R.string.config_icon_mask));
    }
    mMask = PathParser.createPathFromPathData(
        Resources.getSystem().getString(R.string.config_icon_mask));
    mMaskMatrix = new Matrix();
    mCanvas = new Canvas();
    mTransparentRegion = new Region();
}

此方法的Resources.getSystem().getString(R.string.config_icon_mask)，通过getString方法，如果id是config_icon_mask，则返回的是mOverrideValue，mOverrideValue就是上面5种里面的一种。

四.Launcher是如何获取应用图标的:

public Drawable getFullResIcon(LauncherActivityInfo info) {

return mIconProvider.getIcon(info, mIconDpi);
}

 public Drawable getIcon(LauncherActivityInfo info, int iconDpi) {
    return info.getIcon(iconDpi);
}

最终调用到LauncherActivityInfo的getIcon方法

/**
* Returns the icon for this activity, without any badging for the profile

 * @param density The preferred density of the icon, zero for default density. Use
 * density DPI values from {@link DisplayMetrics}.
 * @see #getBadgedIcon(int)
 * @see DisplayMetrics
 * @return The drawable associated with the activity.
 */

public Drawable getIcon(int density) {
    // TODO: Go through LauncherAppsService
    final int iconRes = mActivityInfo.getIconResource();
    Drawable icon = null;
    // Get the preferred density icon from the app's resources
    if (density != 0 && iconRes != 0) {
        try {
            final Resources resources
                    = mPm.getResourcesForApplication(mActivityInfo.applicationInfo);
            icon = resources.getDrawableForDensity(iconRes, density);
        } catch (NameNotFoundException | Resources.NotFoundException exc) {
        }
    }
    // Get the default density icon
    if (icon == null) {
        icon = mActivityInfo.loadIcon(mPm);
    }
    return icon;
}

通过以上步骤可以看出，Launcher获取应用图标的时候时候，如果该应用是支持AdaptiveIcon的话，返回的图标就是根据形状裁剪出来的AdaptiveIconDrawable，Launcher从系统拿到的图标已经是想要的形状图标了。
这就是在把launcher进程kill掉，重启 launcher 重新获取加载就是被裁减过的Icon形状了。