问题
I'm trying to achieve this effect:
The idea is that I want to cover an ImageView
with a partial transparent layer, but not all of it. Somewhere there is an area (circle or rectangle), that should be completely transparent. I tried it using this lines of code:
Paint paint = new Paint();
paint.setColor(Color.parseColor("#80000000"));
canvas.drawRect(0, 0, bitmap.getWidth(), bitmap.getHeight(), paint);
paint.setColor(Color.TRANSPARENT);
canvas.drawCircle((int) x, (int) y, 50, paint);
but it didn't work since under the circle there is the rectangle. Is there anyway to achieve what I'm trying to?
回答1:
Sorry for the late answer. You can achieve this my making a CustomImageView and do as follow.
public class CustomImageView extends ImageView {
private Paint paint;
private Paint transParentPaint;
private Canvas tempCanvas;
private Bitmap emptyBitmap;
public CustomImageView(Context context, AttributeSet attrs, int defStyle) {
super(context, attrs, defStyle);
init();
}
public CustomImageView(Context context) {
super(context);
init();
}
public CustomImageView(Context context, AttributeSet attrs) {
super(context, attrs);
init();
}
private void init() {
paint = new Paint();
paint.setColor(Color.parseColor("#80000000")); //Semi TransParent Paint
transParentPaint = new Paint();
transParentPaint.setColor(Color.TRANSPARENT);
transParentPaint.setXfermode(new PorterDuffXfermode(PorterDuff.Mode.CLEAR));//This is necessary to make the portion transparent. Otherwise it will show Black.
}
@Override
protected void onDraw(Canvas canvas) {
emptyBitmap = Bitmap.createBitmap(getWidth(), getHeight(), Bitmap.Config.ARGB_8888);
tempCanvas = new Canvas(emptyBitmap);
emptyBitmap.eraseColor(Color.TRANSPARENT);
// tempCanvas.drawColor(Color.parseColor("#80000000"));
tempCanvas.drawRect(0, 0, getWidth(), getHeight(), paint);
tempCanvas.drawCircle(getWidth() / 2, getHeight() / 2, 100, transParentPaint); // Set the circle at the middle of the Canvas.
canvas.drawBitmap(emptyBitmap, 0, 0, null);
}
}
Add this CustomImageView to your layout file
<?xml version="1.0" encoding="utf-8"?>
<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:tools="http://schemas.android.com/tools"
android:id="@+id/activity_main"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:paddingBottom="@dimen/activity_vertical_margin"
android:paddingLeft="@dimen/activity_horizontal_margin"
android:paddingRight="@dimen/activity_horizontal_margin"
android:paddingTop="@dimen/activity_vertical_margin"
>
<transparent.example.com.partialtransparentview.CustomImageView
android:id="@+id/image_view"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:background="@drawable/your_image" />
</RelativeLayout>
It will work as you expected.
来源:https://stackoverflow.com/questions/41261764/android-canvas-focus-in-selected-area