将动态子视图垂直添加到ConstraintLayout

视图可以添加到 ConstraintLayout 使用 addView() 就像你和我一样 LinearLayout .不同之处在于 约束青年 添加的视图必须受到约束。要以编程方式约束视图,请使用 ConstraintSet .

此类允许您以编程方式定义一组约束,以与ConstraintLayout一起使用。它允许您创建和保存约束,并将其应用于现有的ConstraintLayout。

下面是一个简单的例子:

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定义两个 TextViews .将其水平居中并放置在顶部。

<android.support.constraint.ConstraintLayout 
    android:id="@+id/constraintLayout"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    tools:context=".MainActivity">

    <TextView
        android:id="@+id/topView"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_marginTop="16dp"
        android:text="Top View"
        android:textSize="20sp"
        app:layout_constraintEnd_toEndOf="parent"
        app:layout_constraintStart_toStartOf="parent"
        app:layout_constraintTop_toTopOf="parent" />

    <TextView
        android:id="@+id/bottomView"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_marginTop="16dp"
        android:text="Bottom View"
        android:textSize="20sp"
        app:layout_constraintEnd_toEndOf="parent"
        app:layout_constraintStart_toStartOf="parent"
        app:layout_constraintTop_toBottomOf="@id/topView" />

</android.support.constraint.ConstraintLayout>

这就是当一个新的 TextView (“中间视图”)添加到此布局中,而不设置约束。请注意,新视图默认为位置(0,0)。

假设我们希望生成的中间视图位于窗口中水平居中的俯视图和俯视图之间,如下所示:

下面是生成此结果的代码:

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

    // Define the new TextView and add it to the ConstraintLayout. Without constraints,
    // this view will be positioned at (0,0).
    TextView middleView = new TextView(this);
    middleView.setId(View.generateViewId());
    middleView.setText("Middle View");
    middleView.setTextSize(TypedValue.COMPLEX_UNIT_DIP, 20.0f);
    ConstraintLayout layout = findViewById(R.id.constraintLayout);
    ConstraintLayout.LayoutParams lp =
        new ConstraintLayout.LayoutParams(ConstraintLayout.LayoutParams.WRAP_CONTENT,
                                          ConstraintLayout.LayoutParams.WRAP_CONTENT);
    layout.addView(middleView, lp);

    // Move the new view into place by applying constraints.
    ConstraintSet set = new ConstraintSet();
    // Get existing constraints. This will be the base for modification.
    set.clone(layout);
    int topMargin = (int) TypedValue.applyDimension(TypedValue.COMPLEX_UNIT_DIP,
                                                    16, getResources().getDisplayMetrics());
    // Set up the connections for the new view. Constrain its top to the bottom of the top view.
    set.connect(middleView.getId(), ConstraintSet.TOP, R.id.topView, ConstraintSet.BOTTOM, topMargin);
    // Constrain the top of the bottom view to the bottom of the new view. This will replace
    // the constraint from the bottom view to the bottom of the top view.
    set.connect(R.id.bottomView, ConstraintSet.TOP, middleView.getId(), ConstraintSet.BOTTOM, topMargin);
    // Since views must be constrained vertically and horizontally, establish the horizontal
    // constaints such that the new view is centered.
    set.centerHorizontally(middleView.getId(),ConstraintSet.PARENT_ID);
    // Finally, apply our good work to the layout.
    set.applyTo(layout);
}