android - 如何使android中 View 周围的区域变暗？

Question

我正在尝试进行一项需要将​​方形区域显示为重点的 Activity 。到目前为止，我已经这样做了。

现在我想要的是将正方形外的区域调暗。使用 framelayout 会使整个 View 变暗。我只想调暗广场外的区域。

Answer 1

您可以绘制一个黑色半透明矩形，然后使用 paint.setXfermode(new PorterDuffXfermode(PorterDuff.Mode.SRC_OUT));

绘制一个内部矩形

由于我对您的布局一无所知，我给出了一个包含 CustomOverlay 类的完整示例:

my_activity.xml

<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:tools="http://schemas.android.com/tools"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:orientation="vertical">

    <fragment
        android:layout_width="match_parent"
        android:layout_height="match_parent"
        android:id="@+id/map"
        android:name="com.google.android.gms.maps.SupportMapFragment" />

    <mypackage.CustomOverlay
        android:layout_width="match_parent"
        android:layout_height="match_parent"
        android:layout_centerInParent="true" />

</RelativeLayout>

(我使用 map 作为基础 View 而不是相机)

CustomOverlay.java

public class CustomOverlay extends LinearLayout {
    private Bitmap windowFrame;

    public CustomOverlay(Context context) {
        super(context);
    }

    public CustomOverlay(Context context, AttributeSet attrs) {
        super(context, attrs);
    }

    public CustomOverlay(Context context, AttributeSet attrs, int defStyleAttr) {
        super(context, attrs, defStyleAttr);
    }

    @TargetApi(Build.VERSION_CODES.LOLLIPOP)
    public CustomOverlay(Context context, AttributeSet attrs, int defStyleAttr, int defStyleRes) {
        super(context, attrs, defStyleAttr, defStyleRes);
    }

    @Override
    protected void dispatchDraw(Canvas canvas) {
        super.dispatchDraw(canvas);

        if (windowFrame == null) {
            createWindowFrame();
        }
        canvas.drawBitmap(windowFrame, 0, 0, null);
    }

    @Override
    public boolean isEnabled() {
        return false;
    }

    @Override
    public boolean isClickable() {
        return false;
    }

    protected void createWindowFrame() {
        windowFrame = Bitmap.createBitmap(getWidth(), getHeight(), Bitmap.Config.ARGB_8888);
        Canvas osCanvas = new Canvas(windowFrame);

        RectF outerRectangle = new RectF(0, 0, getWidth(), getHeight());

        Paint paint = new Paint(Paint.ANTI_ALIAS_FLAG);
        paint.setColor(Color.argb(150, 0, 0, 0));
        osCanvas.drawRect(outerRectangle, paint);

        paint.setXfermode(new PorterDuffXfermode(PorterDuff.Mode.SRC_OUT));
        RectF innerRectangle = new RectF(100, 200, getWidth() - 100, getHeight() - 200);
        osCanvas.drawRect(innerRectangle, paint);

        paint = new Paint(Paint.ANTI_ALIAS_FLAG);
        paint.setStrokeWidth(5);
        paint.setColor(Color.WHITE);
        paint.setStyle(Paint.Style.STROKE);
        osCanvas.drawRect(innerRectangle, paint);
    }

    @Override
    public boolean isInEditMode() {
        return true;
    }

    @Override
    protected void onLayout(boolean changed, int l, int t, int r, int b) {
        super.onLayout(changed, l, t, r, b);
        windowFrame = null;
    }
}

结果是这样的: