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问题来源

在进行日常测试时，测试组发现当Android 9的机器更换了黑色(或者深色背景的壁纸后)，会导致下拉状态栏中的QS(快速设置项)变得异常，如下图

从上述对比图中可知，异常情况下，不见图标颜色加深变黑，连QS Label也消失了。

问题解析

根据出现问题的步骤，我们复现该问题(也就是切换黑色壁纸，并下拉状态栏)，并打印日志查看原因。

2021-12-23 15:25:44.481 735-756/system_process W/WallpaperManagerService: Cannot get theme colors because WallpaperColors is null.
2021-12-23 15:25:45.308 926-926/com.android.systemui D/Tonal: Tonal Palette - index: 1. Main color: ff013631
    Colors: ff011d1a, ff013631, ff014f44, ff026d5d, ff039276, ff03b8a7, ff04ddc9, ff37ead9, ff4cfcf7, ff6bfcfc, ff8ef7fd, ffc0fafe, ffe3fefe
2021-12-23 15:25:45.308 926-926/com.android.systemui D/Tonal: Tonal Palette - index: 1. Main color: ff013631
    Colors: ff011d1a, ff013631, ff014f44, ff026d5d, ff039276, ff03b8a7, ff04ddc9, ff37ead9, ff4cfcf7, ff6bfcfc, ff8ef7fd, ffc0fafe, ffe3fefe
2021-12-23 15:25:51.243 926-926/com.android.systemui D/QSTileBaseView: handleStateChanged, circleColor -16743049, state: SignalState[,icon=ResourceIcon[resId=0x7f0802e5],iconSupplier=null,label=test-network,secondaryLabel=null,contentDescription=WLAN,WLAN 信号满格。,Koridy-test,dualLabelContentDescription=打开WLAN设置。,expandedAccessibilityClassName=android.widget.Switch,disabledByPolicy=false,dualTarget=true,isTransient=false,state=2,slash="isSlashed=false,rotation=6.0",value=true,activityIn=false,activityOut=false]

可以发现，当我们切换了壁纸后，会打印出

D/Tonal: Tonal Palette - index: 1. Main color: ff013631

查找下在哪里输出这个打印

wayhoi@ubuntu20.04$ find ./ -name "*.java" | xargs grep "Tonal Palette" -s
./packages/apps/Launcher3/src_ui_overrides/com/android/launcher3/uioverrides/dynamicui/ColorExtractionAlgorithm.java:        // the Material Tonal Palette defines hues from 0 to 1.
./frameworks/base/core/java/com/android/internal/colorextraction/types/Tonal.java:        // the Material Tonal Palette defines hues from 0 to 1.
./frameworks/base/core/java/com/android/internal/colorextraction/types/Tonal.java:            StringBuilder builder = new StringBuilder("Tonal Palette - index: " + fitIndex +

根据查找结果，查看类frameworks/base/core/java/com/android/internal/colorextraction/types/Tonal.java

public class Tonal implements ExtractionType {
   	//省略代码
	public void extractInto(@Nullable WallpaperColors inWallpaperColors,
            @NonNull GradientColors outColorsNormal, @NonNull GradientColors outColorsDark,
            @NonNull GradientColors outColorsExtraDark) {
        	//调用处
        	boolean success = runTonalExtraction(inWallpaperColors, outColorsNormal, outColorsDark,outColorsExtraDark);
        	if (!success) {
            	applyFallback(inWallpaperColors, outColorsNormal, outColorsDark, outColorsExtraDark);
        	}
    	}   
   
    	private boolean runTonalExtraction(@Nullable WallpaperColors inWallpaperColors,
            @NonNull GradientColors outColorsNormal, @NonNull GradientColors outColorsDark,
            @NonNull GradientColors outColorsExtraDark) {
         	//省略代码
         	if (DEBUG) {
            	StringBuilder builder = new StringBuilder("Tonal Palette - index: " + fitIndex +
                    	". Main color: " + Integer.toHexString(getColorInt(fitIndex, h, s, l)) +
                    	"\nColors: ");
        	}
        	//省略代码
    	}
}

发现源头在Tonal.extractInto(WallpaperColors inWallpaperColors, GradientColors outColorsNormal, GradientColors outColorsDark,GradientColors outColorsExtraDark),我们在该方法处加入调用栈打印，看看相关调用。

根据调用栈的日志打印，最终发现最初的调用者在frameworks\base\packages\SystemUI\src\com\android\systemui\statusbar\phone\StatusBar.java的mColorExtractor.addOnColorsChangedListener(this);中，我们看一下该接口：

frameworks\base\core\java\com\android\internal\colorextraction\ColorExtractor.java

public interface OnColorsChangedListener {
        void onColorsChanged(ColorExtractor colorExtractor, int which);
}

在StatusBar.java中查看具体实现

@Override
public void onColorsChanged(ColorExtractor extractor, int which) {
    updateTheme();
}

/**
  * Switches theme from light to dark and vice-versa.
  */
protected void updateTheme() {
    final boolean inflated = mStackScroller != null;

    // The system wallpaper defines if QS should be light or dark.
    WallpaperColors systemColors = mColorExtractor
        .getWallpaperColors(WallpaperManager.FLAG_SYSTEM);
    final boolean useDarkTheme = systemColors != null
        && (systemColors.getColorHints() & WallpaperColors.HINT_SUPPORTS_DARK_THEME) != 0;
    if (isUsingDarkTheme() != useDarkTheme) {
        mUiOffloadThread.submit(() -> {
            try {
                mOverlayManager.setEnabled("com.android.systemui.theme.dark",
                                           useDarkTheme, mLockscreenUserManager.getCurrentUserId());
            } catch (RemoteException e) {
                Log.w(TAG, "Can't change theme", e);
            }
        });
    }

    // Lock wallpaper defines the color of the majority of the views, hence we'll use it
    // to set our default theme.
    final boolean lockDarkText = mColorExtractor.getColors(WallpaperManager.FLAG_LOCK, true
                                                           /* ignoreVisibility */).supportsDarkText();
    final int themeResId = lockDarkText ? R.style.Theme_SystemUI_Light : R.style.Theme_SystemUI;
    if (mContext.getThemeResId() != themeResId) {
        mContext.setTheme(themeResId);
        if (inflated) {
            onThemeChanged();
        }
    }

    if (inflated) {
        int which;
        if (mState == StatusBarState.KEYGUARD || mState == StatusBarState.SHADE_LOCKED) {
            which = WallpaperManager.FLAG_LOCK;
        } else {
            which = WallpaperManager.FLAG_SYSTEM;
        }
        final boolean useDarkText = mColorExtractor.getColors(which,
                                                              true /* ignoreVisibility */).supportsDarkText();
        mStackScroller.updateDecorViews(useDarkText);

        // Make sure we have the correct navbar/statusbar colors.
        mStatusBarWindowManager.setKeyguardDark(useDarkText);
    }
}

可以注意到上述updateTheme()方法中，有一段注释

// The system wallpaper defines if QS should be light or dark.
// Translate：系统壁纸定义了QS应该是亮还是暗。
WallpaperColors systemColors = mColorExtractor
    .getWallpaperColors(WallpaperManager.FLAG_SYSTEM);
final boolean useDarkTheme = systemColors != null
    && (systemColors.getColorHints() & WallpaperColors.HINT_SUPPORTS_DARK_THEME) != 0;
if (isUsingDarkTheme() != useDarkTheme) {
    mUiOffloadThread.submit(() -> {
        try {
            mOverlayManager.setEnabled("com.android.systemui.theme.dark",
                                       useDarkTheme, mLockscreenUserManager.getCurrentUserId());
        } catch (RemoteException e) {
            Log.w(TAG, "Can't change theme", e);
        }
    });
}

于是，我们就找到了问题根源所在之处，接下来要做的就是阅读上述代码，进行逻辑修改。

我们需要的是，切换黑色/深色壁纸后，QS的颜色不变。

可以注意到

final boolean useDarkTheme = systemColors != null
    && (systemColors.getColorHints() & WallpaperColors.HINT_SUPPORTS_DARK_THEME) != 0;

mOverlayManager.setEnabled("com.android.systemui.theme.dark",
                           useDarkTheme, mLockscreenUserManager.getCurrentUserId());

boolean useDarkTheme = systemColors != null, 见文知意，可以猜测出，这个值就是是否根据壁纸颜色来调节QS的颜色(主题)，因为我们始终不需要黑色，所以我们将userDarkTheme固定为false。

WallpaperColors systemColors = mColorExtractor.getWallpaperColors(WallpaperManager.FLAG_SYSTEM);
final boolean useDarkTheme = systemColors != null
    	&& (systemColors.getColorHints() & WallpaperColors.HINT_SUPPORTS_DARK_THEME) != 0;
if (isUsingDarkTheme() != useDarkTheme) {
    mUiOffloadThread.submit(() -> {
        try {
            mOverlayManager.setEnabled("com.android.systemui.theme.dark",
+                                       /// M: modify by wayhoi, QS close dark theme @{
-					useDarkTheme, mLockscreenUserManager.getCurrentUserId());
+	    		 		false/*useDarkTheme*/, mLockscreenUserManager.getCurrentUserId());
+            				/// }
        } catch (RemoteException e) {
            Log.w(TAG, "Can't change theme", e);
        }
    });
}

刷机，测试，复现步骤走一遍，发现结果如我们预期及需求。

总结

该问题其实来源于Android 9的特性，加入了主题（黑色主题、白色主题、自动主题(根据壁纸的颜色来判定为是黑还是白主题)），过程中，打印日志很重要，同时要注意的一点就是，取好一个变量名也十分重要，如文中出现的useDarkTheme，让我可以一看到就知道这里就是控制主题的。