What other constraints does layout_constraintGuide

I have a ConstraintLayout containing two custom text views. When I try using a percentage it causes the app to crash with a complaint about a null anchor. However the anchors seem valid to me.

I've been through a process of trial and error and no attempt has avoided the crash (for example removing app:layout_constraintEnd_toStartOf="@ id/b" or setting it to app:layout_constraintEnd_toEndOf="parent")

The Layout

<androidx.constraintlayout.widget.ConstraintLayout
    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">

<com.custom.TextInputView
    android:id="@ id/a"
    android:layout_width="wrap_content"
    android:layout_height="wrap_content"
    app:layout_constraintStart_toStartOf="parent"
    app:layout_constraintEnd_toStartOf="@ id/b"
    app:layout_constraintTop_toBottomOf="@id/c_notshown_in_example"
    app:layout_constraintGuide_percent="0.45" />

<com.custom.TextInputView
    android:id="@ id/b"
    android:layout_width="0dp"
    android:layout_height="wrap_content"
    android:layout_marginStart="@dimen/u2"
    android:layout_marginEnd="@dimen/u2"
    app:layout_constraintEnd_toEndOf="parent"
    app:layout_constraintStart_toEndOf="@id/a"
    app:layout_constraintTop_toTopOf="@id/a" />

The Crash:

java.lang.NullPointerException: Attempt to invoke virtual method 'int androidx.constraintlayout.core.widgets.ConstraintAnchor.getFinalValue()' on a null object reference at androidx.constraintlayout.core.widgets.analyzer.Direct.horizontalSolvingPass(Direct.java:328) at androidx.constraintlayout.core.widgets.analyzer.Direct.solvingPass(Direct.java:254) at androidx.constraintlayout.core.widgets.ConstraintWidgetContainer.layout(ConstraintWidgetContainer.java:693) at androidx.constraintlayout.core.widgets.analyzer.BasicMeasure.solveLinearSystem(BasicMeasure.java:160) at androidx.constraintlayout.core.widgets.analyzer.BasicMeasure.solverMeasure(BasicMeasure.java:291) at androidx.constraintlayout.core.widgets.ConstraintWidgetContainer.measure(ConstraintWidgetContainer.java:120) a at

What horizontal constraints does the percentage usage require? (since it fails at horizontalSolvingPass)

CodePudding user response：

The idea will be to wire the ConstraintLayout to the Guideline and everything beside that (e.g. TextView etc.) to the ConstraintLayout for a responsive design.

My example shows it with 2 TextView that are exactly 80% vertically for instance and 45% and 55% in width (app:layout_constraintGuide_percent="0.45"). Important is to set the TextViews width and height to 0dp and to attach to the Guideline:

<?xml version="1.0" encoding="utf-8"?>
<androidx.constraintlayout.widget.ConstraintLayout 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">

    <!-- Vertical Guideline for Text1 (here e.g. 45%) -->
    <androidx.constraintlayout.widget.Guideline
        android:id="@ id/vertical_guideline1"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:orientation="vertical"
        app:layout_constraintGuide_percent="0.45" />

    <!-- Horizontal Guideline for both Texts (here e.g. 80%)-->
    <androidx.constraintlayout.widget.Guideline
        android:id="@ id/horizontal_guideline"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:orientation="horizontal"
        app:layout_constraintGuide_percent="0.8" />

    <!-- TextView1 in Blue -->
    <TextView
        android:id="@ id/textView1"
        android:layout_width="0dp"
        android:layout_height="0dp"
        android:background="#2962FF"
        android:textColor="@color/white"
        app:layout_constraintBottom_toTopOf="@ id/horizontal_guideline"
        app:layout_constraintEnd_toStartOf="@ id/vertical_guideline1"
        app:layout_constraintStart_toStartOf="parent"
        app:layout_constraintTop_toTopOf="parent"
        tools:text="TextView1 in Blue 45%" />

    <!-- TextView2 in Orange -->
    <TextView
        android:id="@ id/textView2"
        android:layout_width="0dp"
        android:layout_height="0dp"
        android:background="#FF6D00"
        android:textColor="@color/white"
        app:layout_constraintBottom_toTopOf="@ id/horizontal_guideline"
        app:layout_constraintEnd_toEndOf="parent"
        app:layout_constraintStart_toStartOf="@ id/vertical_guideline1"
        app:layout_constraintTop_toTopOf="parent"
        tools:text="TextView2 in Orange 55%" />

</androidx.constraintlayout.widget.ConstraintLayout>

RESULT:

CodePudding user response：

There are a few problems with the constraints on your @ id/a view:

The correct percentage constraint is app:layout_constraintWidth_percent
You should use 0dp for the width when using percents
You should constrain both sides of the view to the parent (to define the width is a percentage of)

Once you've done that, you will also have to add bias to the view in order to position it on the far left of the screen:

app:layout_constraintHorizontal_bias="0"

Altogether, your first view should look like this:

<com.custom.TextInputView
    android:id="@ id/a"
    android:layout_width="0dp"
    android:layout_height="wrap_content"
    app:layout_constraintTop_toBottomOf="@id/c_notshown_in_example"
    app:layout_constraintStart_toStartOf="parent"
    app:layout_constraintEnd_toEndOf="parent"
    app:layout_constraintWidth_percent="0.45"
    app:layout_constraintHorizontal_bias="0" />