问题
I just began learning Constraint Layout and it's pretty cool, I have come to topic ConstraintSet and got stuck.
I have seen an example of ConstraintSet in developer documentation but I am not able to get the idea, I have implemented the code as it is and it's working but I am really unclear about the concept.
How constraints work in different ConstraintSet is all I want to know about.
Here is what i have done:
activity_main.xml
<?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"
xmlns:tools="http://schemas.android.com/tools"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:id="@+id/act_main"
tools:context="com.reversebits.constraintanimdemo.MainActivity">
<TextView
android:layout_width="0dp"
android:layout_height="wrap_content"
android:layout_marginEnd="8dp"
android:layout_marginStart="8dp"
android:text="Lorem Ipsum is simply dummy text of the printing and typesetting industry. Lorem Ipsum has been the industry's standard dummy text ever since the 1500s, when an unknown printer took a galley of type and scrambled it to make a type specimen book. It has survived not only five centuries, but also the leap into electronic typesetting, remaining essentially unchanged. It was popularised in the 1960s with the release of Letraset sheets containing Lorem Ipsum passages, and more recently with desktop publishing software like Aldus PageMaker including versions of Lorem Ipsum"
app:layout_constraintEnd_toStartOf="@+id/guideline2"
app:layout_constraintStart_toStartOf="parent"
app:layout_constraintTop_toTopOf="parent"
android:layout_marginTop="8dp" />
<ImageView
android:id="@+id/imageView"
android:layout_width="0dp"
android:layout_height="160dp"
app:srcCompat="@mipmap/ic_launcher"
app:layout_constraintEnd_toEndOf="parent"
android:layout_marginEnd="8dp"
app:layout_constraintTop_toTopOf="parent"
android:layout_marginTop="8dp"
app:layout_constraintStart_toStartOf="@+id/guideline2"
android:layout_marginStart="8dp" />
<android.support.constraint.Guideline
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:id="@+id/guideline"
android:orientation="vertical"
app:layout_constraintGuide_end="364dp" />
<android.support.constraint.Guideline
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:id="@+id/guideline2"
android:orientation="vertical"
app:layout_constraintGuide_percent="0.5" />
<Button
android:onClick="foo"
android:id="@+id/button"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:text="Button"
android:layout_marginBottom="8dp"
app:layout_constraintBottom_toBottomOf="parent"
app:layout_constraintEnd_toEndOf="parent"
android:layout_marginEnd="8dp"
android:layout_marginRight="8dp"/>
</android.support.constraint.ConstraintLayout>
clone.xml
<?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"
xmlns:tools="http://schemas.android.com/tools"
android:layout_width="match_parent"
android:layout_height="match_parent"
tools:context="com.reversebits.constraintanimdemo.MainActivity">
<TextView
android:layout_width="0dp"
android:layout_height="wrap_content"
android:text="Lorem Ipsum is simply dummy text of the printing and typesetting industry. Lorem Ipsum has been the industry's standard dummy text ever since the 1500s, when an unknown printer took a galley of type and scrambled it to make a type specimen book. It has survived not only five centuries, but also the leap into electronic typesetting, remaining essentially unchanged. It was popularised in the 1960s with the release of Letraset sheets containing Lorem Ipsum passages, and more recently with desktop publishing software like Aldus PageMaker including versions of Lorem Ipsum"
app:layout_constraintStart_toStartOf="parent"
android:layout_marginEnd="8dp"
app:layout_constraintEnd_toEndOf="parent"
android:layout_marginStart="8dp"
android:id="@+id/textView"
app:layout_constraintTop_toTopOf="parent"
android:layout_marginTop="8dp" />
<ImageView
android:id="@+id/imageView"
android:layout_width="0dp"
android:layout_height="160dp"
app:srcCompat="@mipmap/ic_launcher"
app:layout_constraintEnd_toEndOf="parent"
android:layout_marginEnd="8dp"
app:layout_constraintStart_toStartOf="parent"
android:layout_marginStart="8dp"
app:layout_constraintBottom_toBottomOf="parent"
android:layout_marginBottom="8dp"
android:layout_marginTop="8dp"
app:layout_constraintTop_toBottomOf="@+id/textView" />
<Button
android:onClick="foo"
android:id="@+id/button"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:text="Button"
android:layout_marginBottom="8dp"
app:layout_constraintBottom_toBottomOf="parent"
app:layout_constraintEnd_toEndOf="parent"
android:layout_marginEnd="8dp"
android:layout_marginRight="8dp"/>
</android.support.constraint.ConstraintLayout>
and MainActivity goes here:
import android.content.Context;
import android.os.Build;
import android.support.constraint.ConstraintLayout;
import android.support.constraint.ConstraintSet;
import android.support.v7.app.AppCompatActivity;
import android.os.Bundle;
import android.transition.TransitionManager;
import android.view.View;
public class MainActivity extends AppCompatActivity {
ConstraintSet mConstraintSet1 = new ConstraintSet(); // create a Constraint Set
ConstraintSet mConstraintSet2 = new ConstraintSet(); // create a Constraint Set
ConstraintLayout mConstraintLayout; // cache the ConstraintLayout
boolean mOld = true;
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
Context context = this;
mConstraintSet2.clone(context, R.layout.clone); // get constraints from layout
setContentView(R.layout.activity_main);
mConstraintLayout = (ConstraintLayout) findViewById(R.id.act_main);
mConstraintSet1.clone(mConstraintLayout); // get constraints from ConstraintSet
}
public void foo(View view) {
if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.KITKAT) {
TransitionManager.beginDelayedTransition(mConstraintLayout);
}
if (mOld = !mOld) {
mConstraintSet1.applyTo(mConstraintLayout); // set new constraints
} else {
mConstraintSet2.applyTo(mConstraintLayout); // set new constraints
}
}
}
回答1:
Let's say you want to move around some views after a button click. You define a layout in activity_main.xml for example, with the button in it. To get the ConstraintSet of the main layout, mConstraintSet1.clone(mConstraintLayout) is called. The secondary layout (the layout that you want to display after the button click) is cloned from the secondary layout file, clone.xml. That layout contains the same views with the same id's, but with other constraints applied to them.
After the user clicks the button, foo() is executed. foo() starts an animated Transition and then applies the desired ConstraintSet to the ConstraintLayout, causing the views to move around. Because of the TransitionManager call, the movement is animated.
来源：https://stackoverflow.com/questions/44697342/how-exactly-constraintset-works-with-constraintlayouts-in-android