How to create transparent semicircle? [closed]

问题

I want to create this effect.TextView with transparent semicircle as backgound .

I tried add drawable as background.

<?xml version="1.0" encoding="utf-8"?>
<shape xmlns:android="http://schemas.android.com/apk/res/android" android:shape="oval" >
    <solid android:color="#00000000" />
</shape>

also i tried this stackoverflow similar question ,but it doesn't work for me. Can anyone help me?

回答1:

You cannot create a semicircle from xml. but you could achieve what you are looking for using a circle with appropriate margin & padding.

Create a fixed sized circle like this:

<?xml version="1.0" encoding="utf-8"?>
<shape xmlns:android="http://schemas.android.com/apk/res/android"
    android:shape="oval"
    android:useLevel="false" >
    <solid android:color="#006AC5" />
    <size
        android:height="50dp"
        android:width="50dp" />
</shape>

Now use it as the background of your TextView like this:

<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:background="#FFFF00">

    <ImageView
        android:contentDescription="@string/app_name"
        android:id="@+id/img"
        android:layout_width="fill_parent"
        android:layout_height="200dip"
        android:layout_alignParentTop="true"
        android:background="#006AC5" />

    <TextView 
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_below="@id/img"
        android:layout_marginTop="-35dip"
        android:paddingTop="10dip"
        android:background="@drawable/circle"
        android:layout_centerHorizontal="true"
        android:text="@string/one"
        android:gravity="center"/>

</RelativeLayout>

Now if you give a top margin of -25dip (half of circle's height) to your TextView, you'll get a perfect semicircle in the bottom, but I've added just another 10dip (& 10dip padding to keep the text in place) just to get a closer look to what you're looking for.

If you further want to change background of the top ImageView & you don't want the rest of the circle to mess with the looks, you could just add the ImageView after you add the TextView so it would have a higher z-index, & then use a separate TextView to display text above the Image. It's quite nasty I know, but it should work :)

来源：https://stackoverflow.com/questions/20035902/how-to-create-transparent-semicircle

标签

android

user-interface

view

drawable