Change Guideline percentage in constraint layout programmatically

Question

I have a guideline in constraint layout like this

<android.support.constraint.Guideline
    android:layout_width="wrap_content"
    android:layout_height="wrap_content"
    android:id="@+id/guideline8"
    app:layout_constraintGuide_percent="0.5"
    android:orientation="vertical"/>

Later I want to change the app:layout_constraintGuide_percent value to something else conditionally. How can I achieve this.

Answer 1

There is two ways to do it:

• Using ConstraintLayout.LayoutParams

This method get a specific parameter from the ConstraintLayout and modify it.

Guideline guideLine = (Guideline) findViewById(R.id.your_guideline);
ConstraintLayout.LayoutParams params = (ConstraintLayout.LayoutParams) guideLine.getLayoutParams();
params.guidePercent = 0.45f; // 45% // range: 0 <-> 1
guideLine.setLayoutParams(params);

• Using ConstraintSet

This method consists in cloning the ConstraintLayout attributes, modifying them and then applying to the View.

BUT it's very slow.

ConstraintLayout constraintLayout = (ConstraintLayout) findViewById(R.id.your_constraint_with_guideline);
ConstraintSet constraintSet = new ConstraintSet();
constraintSet.clone(constraintLayout);        
constraintSet.setGuidelinePercent(R.id.your_guideline, 0.07f); // 7% // range: 0 <-> 1
TransitionManager.beginDelayedTransition(constraintLayout);
constraintSet.applyTo(constraintLayout);

---

Creating a parallax effect

To test those methods I created a parallax animation using a GuideLine and a ScrollView on top.

On the AndroidManifest.xml, inside your Activity, add this: android:hardwareAccelerated="true".

     <activity 
        android:name=".MainActivity"
        android:configChanges="keyboardHidden|orientation|screenSize"
        android:hardwareAccelerated="true">
     ...

MainActivity.java

Guideline guideTopInfo;
ConstraintLayout constraintLayout;
ConstraintLayout.LayoutParams params;
ConstraintSet constraintSet;

@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_main);

    guideTopInfo = (Guideline) findViewById(R.id.guideline2);
    constraintLayout = (ConstraintLayout) findViewById(R.id.constraint_root);
    params = (ConstraintLayout.LayoutParams) guideTopInfo.getLayoutParams();

    //constraintSet = new ConstraintSet();
    //constraintSet.clone(constraintLayout);

    final ScrollView scrollView = (ScrollView) findViewById(R.id.scroll_front);
    scrollView.getViewTreeObserver().addOnScrollChangedListener(new ViewTreeObserver.OnScrollChangedListener() {
        @Override
        public void onScrollChanged() {
            float percentage = scrollView.getScrollY() * 0.0001f; // 0.001f faster // 0.00001f slower parallax animation

            Log.d("mLog", String.valueOf(percentage));
            if(percentage >= 0) {
                // my XML percentage value was 12%
                params.guidePercent = 0.12f - percentage; // up
                //params.guidePercent = 0.12f + percentage; // downm
                guideTopInfo.setLayoutParams(params);

                //constraintSet.setGuidelinePercent(R.id.guideline2, 0.12f - percentage);
                //TransitionManager.beginDelayedTransition(constraintLayout);
                //constraintSet.applyTo(constraintLayout);
            }
        }
    });
}

---

My other answer about parallax if anyone is interested. ;)