介绍三种方案全局设置灰白模式，原理都是相同的，利用Android提供的ColorMatrix（颜色矩阵），将其饱和度设置为0，这样使用Paint绘制出来的都是没有饱和度的灰白样式！

不同的方案只是设置时机不同而已。

Android实现设置灰白模式效果 - 掘金

Android APP全局黑白化实现方案_xiaoerbuyu1233的博客-CSDN博客

最简单方案：监控activity生命周期，在onCreate中置灰

Application里面不是有registerActivityLifecycleCallbacks这个注册监听方法吗？监听里面的onActivityCreated不是可以获取到当前的Activity吗？那DecorView不就拿到了！

public class StudyApp extends Application {@Overridepublic void onCreate() {super.onCreate();Paint mPaint = new Paint();ColorMatrix mColorMatrix = new ColorMatrix();mColorMatrix.setSaturation(0);mPaint.setColorFilter(new ColorMatrixColorFilter(mColorMatrix));registerActivityLifecycleCallbacks(new ActivityLifecycleCallbacks() {@Overridepublic void onActivityCreated(@NonNull Activity activity, @Nullable Bundle savedInstanceState) {// 当Activity创建，我们拿到DecorView，使用Paint进行重绘View decorView = activity.getWindow().getDecorView();decorView.setLayerType(View.LAYER_TYPE_HARDWARE, mPaint);}....});}
}

方案一：给Activity的顶层View设置置灰，实现全局置灰效果

可以在BaseActivity的onCreate方法中，使用ColorMatrix设置灰度

    @Overrideprotected void onCreate(@Nullable Bundle savedInstanceState) {super.onCreate(savedInstanceState);//方案一Paint paint = new Paint();ColorMatrix cm = new ColorMatrix();cm.setSaturation(0);//灰度效果paint.setColorFilter(new ColorMatrixColorFilter(cm));getWindow().getDecorView().setLayerType(View.LAYER_TYPE_HARDWARE,paint);}

方案二：该方法使用自定义layout，在dispatchdraw方法的时候，添加一层黑白色的bitmap，让界面开起来成为黑白模式。

先定义一个GrayFrameLayout布局

public class GrayFrameLayout extends FrameLayout {private Paint mPaint = new Paint();public GrayFrameLayout(@NonNull Context context) {super(context);}public GrayFrameLayout(@NonNull Context context, @Nullable AttributeSet attrs) {super(context, attrs);ColorMatrix cm = new ColorMatrix();cm.setSaturation(0);mPaint.setColorFilter(new ColorMatrixColorFilter(cm));}@Overrideprotected void onDraw(Canvas canvas) {canvas.saveLayer(null, mPaint, Canvas.ALL_SAVE_FLAG);super.onDraw(canvas);}@Overrideprotected void dispatchDraw(Canvas canvas) {canvas.saveLayer(null, mPaint, Canvas.ALL_SAVE_FLAG);super.dispatchDraw(canvas);}
}

在BaseActivity的onCreateView方法中做如下处理：

 	@Overridepublic View onCreateView(View parent, String name, Context context, AttributeSet attrs {//方案二if("FrameLayout".equals(name)){int attributeCount = attrs.getAttributeCount();for (int i = 0; i < attributeCount; i++) {String attributeName = attrs.getAttributeName(i);String attributeValue = attrs.getAttributeValue(i);if(attributeName.equals("id")){int id = Integer.parseInt(attributeValue.substring(1));String resourceName = getResources().getResourceName(id);if("android:id/content".equals(resourceName)){GrayFrameLayout frameLayout  = new GrayFrameLayout(this,attrs);return frameLayout;}}}}return super.onCreateView(parent, name, context, attrs);}

方案三：有些特殊控件需要置灰，比如webview、H5页面、视频等

    //硬件加速置灰方法public void setLayerGrayType(View view) {if (mGrayMatrix == null || mGrayPaint == null) {init();}view.setLayerType(View.LAYER_TYPE_HARDWARE, mGrayPaint);}

特殊控件需要置灰的话直接调用setLayerGrayType()方法将view传进去，比如demo中让某个Activity置灰，那就在Activity里面调用：

GrayManager.getInstance().setLayerGrayType(getWindow().getDecorView());