ConstraintLayout#LayoutParamsを使う. まず、ConstraintLayout上のViewを取得する.

Button button = findViewById(R.id.button);

もしくは、追加したい適当なオブジェクトを作成し、ConstraintLayoutにViewを追加する.

Button button = new Button(this);
constrintLayout.addView(button)

※先にaddViewしないと、次のlayoutParamsにnullが入る(エラーが発生する)ので注意.

次に、上のViewのLayoutParamsを取得し、適当に設定する. 親View(?)と連結したいときは、PARENT_IDを代入する. ほかのViewと連結したいときは、View#getIdメソッドを使う. LayoutParamsのフィールドについては、xmlのものとほとんど同じなので、そちら(例えば、Android Studioのデザインビューとか)を見るとわかりやすいと思う.

ConstraintLayout.LayoutParams layoutParams = (ConstraintLayout.LayoutParams)button.getLayoutParams();
layoutParams.startToEnd = anotherView.getId();
layoutParams.endToEnd = ConstraintLayout.LayoutParams.PARENT_ID;
layoutParams.topToTop = ConstraintLayout.LayoutParams.PARENT_ID;
layoutParams.bottomToBottom = ConstraintLayout.LayoutParams.PARENT_ID;
layoutParams.verticalBias = (float) 0.1;
layoutParams.horizontalBias = (float) 0.1;
button1.setLayoutParams(layoutParams);

最後に、上の変更を適用する.

button.setLayoutParams(layoutParams);

他にもこちらと同様に、ViewのWidthやHeight、Marginを変更できたりする(MarginLinearLayoutにキャストしなくてもよい、次の適用例を参照).

適用例

ConstraintLayout上に2つのボタンを表示させる.

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:id="@+id/constraintLayoutParamsLayout"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    tools:context="com.blogspot.ko-ika.constraintlayoutparams.MainActivity">

    <Button
        android:id="@+id/button1"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text="Button1" />

    <Button
        android:id="@+id/button2"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text="Button2" />
</android.support.constraint.ConstraintLayout>

activity_main.xml

package jp.blogspot.ko-ika.constraintlayoutparams;

import android.support.constraint.ConstraintLayout;
import android.support.v7.app.AppCompatActivity;
import android.os.Bundle;
import android.widget.Button;

public class MainActivity extends AppCompatActivity {

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

        Button button1 = findViewById(R.id.button1);
        Button button2 = findViewById(R.id.button2);

        ConstraintLayout constraintLayout = findViewById(R.id.constraintLayoutParamsLayout);

        // Button1の設定
        ConstraintLayout.LayoutParams layoutParams = (ConstraintLayout.LayoutParams)button1.getLayoutParams();
        layoutParams.topMargin = 8;
        layoutParams.rightMargin = 16;
        layoutParams.startToStart = ConstraintLayout.LayoutParams.PARENT_ID;
        layoutParams.endToEnd = ConstraintLayout.LayoutParams.PARENT_ID;
        layoutParams.topToTop = ConstraintLayout.LayoutParams.PARENT_ID;
        layoutParams.bottomToBottom = ConstraintLayout.LayoutParams.PARENT_ID;
        layoutParams.verticalBias = (float) 0.1;
        layoutParams.horizontalBias = (float) 0.1;
        button1.setLayoutParams(layoutParams);

        // Button2の設定
        layoutParams = (ConstraintLayout.LayoutParams)button2.getLayoutParams();
        layoutParams.leftMargin = 16;
        layoutParams.startToEnd = button1.getId();
        layoutParams.endToEnd = ConstraintLayout.LayoutParams.PARENT_ID;
        layoutParams.topToTop = ConstraintLayout.LayoutParams.PARENT_ID;
        layoutParams.bottomToBottom = ConstraintLayout.LayoutParams.PARENT_ID;
        layoutParams.verticalBias = (float)0.1;
        layoutParams.horizontalBias = 0;
        button2.setLayoutParams(layoutParams);
    }
}

実行例

さらに

ConstraintSetを使うと同じ様に設定できるらしい.

Kotlin(Java)コード上でConstraintLayoutの制約を編集する

が、この方法だと、Biasが設定できない?

また、Viewが実際に配置される(?)まで、そのIDが取得できないみたいなので、注意が必要.
実際に、上の適用例を次のようにしてみる.

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:id="@+id/constraintLayoutParamsLayout"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    tools:context="com.blogspot.ko-ika.constraintlayoutparams.MainActivity">

</android.support.constraint.ConstraintLayout>

activity_main.xml

        

        Button button1 = new Button(this);
        Button button2 = new Button(this);
        ConstraintLayout constraintLayout = findViewById(R.id.constraintLayoutParamsLayout); 

        // Button1の設定
        constraintLayout.addView(button1);
        button1.setText("Button1"); 
        ConstraintLayout.LayoutParams layoutParams = (ConstraintLayout.LayoutParams)button1.getLayoutParams();
        layoutParams.topMargin = 8;
        layoutParams.rightMargin = 16;
        layoutParams.startToStart = ConstraintLayout.LayoutParams.PARENT_ID;
        layoutParams.endToEnd = ConstraintLayout.LayoutParams.PARENT_ID;
        layoutParams.topToTop = ConstraintLayout.LayoutParams.PARENT_ID;
        layoutParams.bottomToBottom = ConstraintLayout.LayoutParams.PARENT_ID;
        layoutParams.verticalBias = (float) 0.1;
        layoutParams.horizontalBias = (float) 0.1;
        button1.setLayoutParams(layoutParams);

        // Button2の設定
        constraintLayout.addView(button2);
        button2.setText("Button2"); 
        layoutParams = (ConstraintLayout.LayoutParams)button2.getLayoutParams();
        layoutParams.leftMargin = 16;
        layoutParams.startToEnd = button1.getId();
        layoutParams.endToEnd = ConstraintLayout.LayoutParams.PARENT_ID;
        layoutParams.topToTop = ConstraintLayout.LayoutParams.PARENT_ID;
        layoutParams.bottomToBottom = ConstraintLayout.LayoutParams.PARENT_ID;
        layoutParams.verticalBias = (float)0.1;
        layoutParams.horizontalBias = 0;
        button2.setLayoutParams(layoutParams);

変更箇所をマークアップした. すると、次のようになってしまう.

参考にしたサイト

ConstraintLayout.LayoutParams | Android Developers

さきいかの備忘録

ConstraintLayoutの制約をJavaで設定する

適用例

さらに

参考にしたサイト

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