ConstraintLayout宽高比

Question

考虑以下布局文件:

<?xml version="1.0" encoding="utf-8"?>
<RelativeLayout
    xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:app="http://schemas.android.com/apk/res-auto"
    xmlns:tools="http://schemas.android.com/tools"
    android:layout_width="match_parent"
    android:layout_height="match_parent">

    <android.support.constraint.ConstraintLayout
        android:id="@+id/activity_main"
        android:layout_width="match_parent"
        android:layout_height="match_parent"
        android:background="#FF0000"
        android:paddingBottom="@dimen/activity_vertical_margin"
        android:paddingLeft="@dimen/activity_horizontal_margin"
        android:paddingRight="@dimen/activity_horizontal_margin"
        android:paddingTop="@dimen/activity_vertical_margin">

        <ImageView
            android:layout_width="0dp"
            android:layout_height="0dp"
            android:background="#0000FF"
            android:padding="16dp"
            app:layout_constraintBottom_toBottomOf="parent"
            app:layout_constraintTop_toTopOf="parent"
            app:layout_constraintLeft_toLeftOf="parent"
            app:layout_constraintDimensionRatio="H,3:1"
            tools:layout_editor_absoluteX="16dp" />

    </android.support.constraint.ConstraintLayout>

</RelativeLayout>

我不确定app:layout_constraintDimensionRatio是如何工作的.我的理解是比例总是宽度:高度.因此3:1将始终使ImageView看起来比高度宽3倍.前缀H或W告诉ConstraintLayout哪个维度应该尊重比率.如果是H则表示首先根据其他约束计算宽度,然后根据纵横比调整高度.然而,这是布局的结果:

高度是宽度的3倍,这是意料之外的.任何人都可以向我解释如何计算尺寸相对于app:layout_constraintDimensionRatio设置？

Answer 1

您对方法的理解app:layout_constraintDimensionRatio是正确的.如果设置app:layout_constraintDimensionRatio="H,3:1"则表示首先根据其他约束计算宽度,然后根据纵横比调整高度.您的实现的唯一问题是您添加app:layout_constraintBottom_toBottomOf="parent"到ImageView,因此它app:layout_constraintDimensionRatio被忽略.

这是使用3:1宽高比调整ImageView大小的布局:

<android.support.constraint.ConstraintLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:app="http://schemas.android.com/apk/res-auto"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:background="#FF0000">

    <ImageView
        android:id="@+id/imageView"
        android:layout_width="0dp"
        android:layout_height="0dp"
        android:layout_marginStart="16dp"
        android:layout_marginTop="16dp"
        android:layout_marginEnd="16dp"
        android:background="#0000FF"
        app:layout_constraintTop_toTopOf="parent"
        app:layout_constraintStart_toStartOf="parent"
        app:layout_constraintEnd_toEndOf="parent"
        app:layout_constraintDimensionRatio="H,3:1" />

</android.support.constraint.ConstraintLayout>

这是结果视图:

Answer 2

基本上,我们有

layout_constraintDimensionRatio(width:height)

例

<!-- button which have width = it's content and height = 1/2 width -->
<Button
        android:layout_width="wrap_content"
        android:layout_height="0dp"
        app:layout_constraintStart_toStartOf="parent" <!-- I still think that we don't need this attribute but I when I don't add this, constraint not working -->
        android:text="Button TEST RATIO 1"
        app:layout_constraintDimensionRatio="2:1" />

产量

<!-- button which have width = it's content and height = 1/2 width -->
<Button
        android:layout_width="wrap_content"
        android:layout_height="0dp"
        app:layout_constraintStart_toStartOf="parent"
        android:text="Button TEST RATIO 2"
        app:layout_constraintDimensionRatio="2" /> <!-- 2 here <=> 2:1 <=> 2/1 (1:1 <=> 1, 1/2 <=> 0.5, ....) ->

产量

<!-- button which have width = match_parent and height = 1/2 width -->
<Button
        android:layout_width="match_parent"
        android:layout_height="0dp"
        android:text="Button TEST RATIO 3"
        app:layout_constraintDimensionRatio="2" />

产量

<!-- button which have width = match constraint and height = 1/2 width -->
<Button
        android:layout_width="0dp"
        android:layout_height="0dp"
        android:text="Button TEST RATIO 4"
        app:layout_constraintStart_toStartOf="parent"
        app:layout_constraintEnd_toEndOf="parent"
        app:layout_constraintDimensionRatio="2" />

产量

演示:https://github.com/PhanVanLinh/AndroidConstraintLayoutRatio

Answer 3

看看这些ImageView属性:

    app:layout_constraintBottom_toBottomOf="parent"
    app:layout_constraintTop_toTopOf="parent"
    app:layout_constraintLeft_toLeftOf="parent"

这些性质覆盖layout_constraintDimensionRatio由于该ImageView被约束到所述底部,顶部和左侧导致主父View占据左,上和主屏幕的底部部分.

    app:layout_constraintBottom_toBottomOf="parent"
    app:layout_constraintTop_toTopOf="parent"
    app:layout_constraintLeft_toLeftOf="parent"
    app:layout_constraintRight_toRightOf="parent"

这将是一个解决方案.layout_constraintBottom_toBottomOf如果希望视图显示在顶部,反之亦然,则可以省略.最好除去所有上述约束,除了layout_constraintDimensionRatio这是最推荐的解决方案.