在ConstraintLayout中引用的视图消失时保留边距

Question

我有2个TextViews,如下面的xml.如果我textView2在运行时隐藏,我会失去底部边距.textView如果textView2消失,我怎样才能保持底部边距和父节点之间的16dp .

<?xml version="1.0" encoding="utf-8"?>
<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="wrap_content">

  <TextView
      android:id="@+id/textView"
      android:layout_width="0dp"
      android:layout_height="wrap_content"
      android:layout_marginBottom="16dp"
      android:layout_marginEnd="8dp"
      android:layout_marginStart="8dp"
      android:layout_marginTop="8dp"
      android:text="abc"
      app:layout_constraintBottom_toTopOf="@+id/textView2"
      app:layout_constraintEnd_toEndOf="parent"
      app:layout_constraintStart_toStartOf="parent"
      app:layout_constraintTop_toTopOf="parent"
      app:layout_constraintVertical_chainStyle="packed"
      />

  <TextView
      android:id="@+id/textView2"
      android:layout_width="0dp"
      android:layout_height="wrap_content"
      android:layout_marginBottom="32dp"
      android:layout_marginEnd="8dp"
      android:layout_marginStart="8dp"
      android:text="xyz"
      app:layout_constraintBottom_toBottomOf="parent"
      app:layout_constraintEnd_toEndOf="parent"
      app:layout_constraintStart_toStartOf="parent"
      app:layout_constraintTop_toBottomOf="@+id/textView"
      app:layout_constraintVertical_chainStyle="packed"/>
</android.support.constraint.ConstraintLayout>

Answer 1

用途layout_goneMarginBottom:

<?xml version="1.0" encoding="utf-8"?>
<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="wrap_content">

  <TextView
      android:id="@+id/textView"
      android:layout_width="0dp"
      android:layout_height="wrap_content"
      android:layout_marginBottom="16dp"
      android:layout_marginEnd="8dp"
      android:layout_marginStart="8dp"
      android:layout_marginTop="8dp"
      android:text="abc"
      app:layout_goneMarginBottom="16dp"
      app:layout_constraintBottom_toTopOf="@+id/textView2"
      app:layout_constraintEnd_toEndOf="parent"
      app:layout_constraintStart_toStartOf="parent"
      app:layout_constraintTop_toTopOf="parent"
      app:layout_constraintVertical_chainStyle="packed"
      />

  <TextView
      android:id="@+id/textView2"
      android:layout_width="0dp"
      android:layout_height="wrap_content"
      android:layout_marginBottom="32dp"
      android:layout_marginEnd="8dp"
      android:layout_marginStart="8dp"
      android:text="xyz"
      app:layout_constraintBottom_toBottomOf="parent"
      app:layout_constraintEnd_toEndOf="parent"
      app:layout_constraintStart_toStartOf="parent"
      app:layout_constraintTop_toBottomOf="@+id/textView"
      app:layout_constraintVertical_chainStyle="packed"/>
</android.support.constraint.ConstraintLayout>

Answer 2

下面的例子有助于理解这个概念

以下是text3的约束

 app:layout_goneMarginStart="100dp"
 app:layout_constraintStart_toEndOf="@id/text2"
 android:layout_marginStart="10dp"

因为我们已经为 text3 设置了 text2 的开始约束

• 当text2可见时，将考虑android:layout_marginStart="10dp"
• 当text2消失时，app:layout_goneMarginStart="100dp"将被视为text3开始约束与text2。

因此，当 startConstraint 消失时，它会考虑 goneMarginStart。类似地，如果 endConstraint 消失，则 goneMarginEnd 将被视为如下