有没有一种方法可以将alpha属性设置为子视图和父视图？

Question

I am developing app where I have set custom drawable to main layout with alpha attribute. But it sets alpha to whole view. and I wanted to set alpha to the only main layout. so that the text which will displayed normally without alpha effect. Present Output

The alpha effect is taken by whole view.

<android.support.constraint.ConstraintLayout
        android:id="@+id/containerLinear"
        android:layout_width="match_parent"
        android:layout_height="match_parent"
        android:background="@drawable/gradient_with_bottom_curve"
        android:orientation="horizontal"
        android:alpha="0.4"
        app:layout_constraintBottom_toBottomOf="parent"
        app:layout_constraintLeft_toLeftOf="parent"
        app:layout_constraintRight_toRightOf="parent"
        app:layout_constraintTop_toTopOf="parent">
        <ScrollView
            android:id="@+id/mainScroll"
            android:layout_width="match_parent"
            android:layout_height="match_parent">
            <LinearLayout
                android:id="@+id/scrollLinear"
                android:layout_width="match_parent"
                android:layout_height="wrap_content"
                android:orientation="horizontal">
                <RelativeLayout
                    android:id="@+id/mainRelative"
                    android:layout_width="match_parent"
                    android:layout_height="match_parent">
                    <TextView
                        android:id="@+id/txtHeading"
                        android:layout_width="match_parent"
                        android:layout_height="wrap_content"
                        android:text="Business Name"
                        android:gravity="center"
                        android:layout_marginTop="10dp"
                        android:padding="5dp"
                        android:textStyle="bold"
                        android:textSize="20sp"
                        android:textColor="@color/logo_orange"/>
                    <RelativeLayout
                        android:id="@+id/paraOneRelative"
                        android:layout_below="@+id/txtHeading"
                        android:layout_width="match_parent"
                        android:layout_height="wrap_content">
                        <TextView
                            android:id="@+id/txtParaOneBold"
                            android:layout_width="wrap_content"
                            android:layout_height="wrap_content"
                            android:text="Some write up"
                            android:gravity="start"
                            android:layout_marginTop="10dp"
                            android:padding="5dp"
                            android:textStyle="normal"
                            android:textSize="12sp"
                            android:textColor="@color/black"/>
                    </RelativeLayout>
                </RelativeLayout>
            </LinearLayout>
        </ScrollView>
    </android.support.constraint.ConstraintLayout>

Answer 1

You need to set the drawable on a view at the same level with the ScrollView

<androidx.constraintlayout.widget.ConstraintLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:id="@+id/containerLinear"
    android:layout_width="match_parent"
    android:layout_height="match_parent">

    <View
        android:layout_width="match_parent"
        android:layout_height="match_parent"
        android:background="@drawable/gradient_with_bottom_curve"
        android:alpha="0.4"/>

    <ScrollView
        android:id="@+id/mainScroll"
        android:layout_width="match_parent"
        android:layout_height="match_parent">

And you'll see that the text inside the TextViews no longer has the alpha.

Not related to the alpha issue, but the ConstraintLayout is useless here. Same for the constraints you set on it. The constraints should go on elements inside the ConstraintLayout . Basically you should have something like this:

FrameLayout
  ScrollView
    ConstraintLayout
      Views

Answer 2

you can try set background for scroll view and try alpha there

<RelativeLayout
                    android:id="@+id/mainRelative"
                    android:layout_width="match_parent"
                    android:layout_height="match_parent"
                    android:alpha="0.4"
                    android:background="@drawable/gradient_with_bottom_curve">

Answer 3

Create an ImageView as a child of ConstraintLayout

<ImageView
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:background="@drawable/gradient_with_bottom_curve"
    android:alpha="0.4"/>

Answer 4

You could use FrameLayout as the base instead of ConstraintLayout and layer the ScrollView on top of a View (which has the translucent background). Something along the following lines should work,

<FrameLayout
    android:id="@+id/containerLinear"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:orientation="horizontal"
    app:layout_constraintBottom_toBottomOf="parent"
    app:layout_constraintLeft_toLeftOf="parent"
    app:layout_constraintRight_toRightOf="parent"
    app:layout_constraintTop_toTopOf="parent">

    <View
        android:layout_width="match_parent"
        android:layout_height="match_parent"
        android:alpha="0.4"
        android:background="@drawable/gradient_with_bottom_curve" />

    <ScrollView
        android:id="@+id/mainScroll"
        android:layout_width="match_parent"
        android:layout_height="match_parent">
        <LinearLayout
            android:id="@+id/scrollLinear"
            android:layout_width="match_parent"
            android:layout_height="wrap_content"
            android:orientation="horizontal">
            <RelativeLayout
                android:id="@+id/mainRelative"
                android:layout_width="match_parent"
                android:layout_height="match_parent">
                <TextView
                    android:id="@+id/txtHeading"
                    android:layout_width="match_parent"
                    android:layout_height="wrap_content"
                    android:text="Business Name"
                    android:gravity="center"
                    android:layout_marginTop="10dp"
                    android:padding="5dp"
                    android:textStyle="bold"
                    android:textSize="20sp"
                    android:textColor="@color/logo_orange"/>
                <RelativeLayout
                    android:id="@+id/paraOneRelative"
                    android:layout_below="@+id/txtHeading"
                    android:layout_width="match_parent"
                    android:layout_height="wrap_content">
                    <TextView
                        android:id="@+id/txtParaOneBold"
                        android:layout_width="wrap_content"
                        android:layout_height="wrap_content"
                        android:text="Some write up"
                        android:gravity="start"
                        android:layout_marginTop="10dp"
                        android:padding="5dp"
                        android:textStyle="normal"
                        android:textSize="12sp"
                        android:textColor="@color/black"/>
                </RelativeLayout>
            </RelativeLayout>
        </LinearLayout>
    </ScrollView>
</FrameLayout>