Java 使用ConstraintSet时，测量的布局大小为零

这快把我逼疯了！当我尝试使用约束布局和约束集以编程方式构建布局时，测量的布局始终为0

我尝试了requestLayout，forceLayout，对所有的孩子和家长无效。但宽度和高度为0，使整个视图不可见

这是我的布局生成器。我的问题是，当我应用约束时，视图呈现为不可见

public final class FormBuilder {

    private Context context;
    private ArrayList<ArrayList<TextInputLayout>> fields;

    private FormBuilder(Context context) {
        this.context = context;
        fields = new ArrayList<>();
        fields.add(new ArrayList<TextInputLayout>());
    }

    private ArrayList<TextInputLayout> getLastRow() {
        return fields.get(fields.size() - 1);
    }

    public static FormBuilder newForm(Context context) {
        return new FormBuilder(context);
    }

    public FormBuilder addField(@NonNull String hint) {
        TextInputLayout field = newTextField(context, hint);
        getLastRow().add(field);
        return this;
    }

    public FormBuilder nextRow() {
        if (getLastRow().size() > 0) fields.add(new ArrayList<TextInputLayout>());
        return this;
    }

    public FormView build() {
        FormView formView = new FormView(context);
        ConstraintSet constraints = new ConstraintSet();

        int topId = ConstraintSet.PARENT_ID;
        for (ArrayList<TextInputLayout> row : fields) {
            if (row.size() == 0) continue;

            int[] rowIds = new int[row.size()];
            for (int i = 0; i < row.size(); i++) { // constraint top
                TextInputLayout field = row.get(i);
                rowIds[i] = field.getId();
                ConstraintLayout.LayoutParams params = new ConstraintLayout.LayoutParams(
                        ConstraintLayout.LayoutParams.WRAP_CONTENT,
                        ConstraintLayout.LayoutParams.WRAP_CONTENT
                );
                formView.addView(field, params);

                if (topId == ConstraintSet.PARENT_ID) {
                    constraints.connect(rowIds[i], ConstraintSet.TOP, ConstraintSet.PARENT_ID, ConstraintSet.TOP);
                } else {
                    constraints.connect(rowIds[i], ConstraintSet.TOP, topId, ConstraintSet.BOTTOM);
                }
            }
            if (row.size() >= 2) { // constraint start and end
                constraints.createHorizontalChainRtl(
                        ConstraintSet.PARENT_ID, ConstraintSet.START,
                        ConstraintSet.PARENT_ID, ConstraintSet.END,
                        rowIds, null, ConstraintSet.CHAIN_SPREAD);
            } else { // row.size = 1
                constraints.connect(rowIds[0], ConstraintSet.START, ConstraintSet.PARENT_ID, ConstraintSet.START);
                constraints.connect(rowIds[0], ConstraintSet.END, ConstraintSet.PARENT_ID, ConstraintSet.END);
            }

            topId = rowIds[0];
        }
        constraints.applyTo(formView); // this turns layout size to zero
        return formView;
    }

    private static TextInputLayout newTextField(Context context, String hint) {
        TextInputLayout.LayoutParams layoutParams = new TextInputLayout.LayoutParams(
                TextInputLayout.LayoutParams.MATCH_PARENT,
                TextInputLayout.LayoutParams.WRAP_CONTENT
        );
        TextInputLayout inputLayout = new TextInputLayout(context);
        TextInputEditText editText = new TextInputEditText(context);
        inputLayout.addView(editText, layoutParams);
        inputLayout.setHint(hint);
        inputLayout.setId(ViewCompat.generateViewId());
        return inputLayout;
    }
}

FormView.java

public class FormView extends ConstraintLayout {

    public FormView(Context context) {
        super(context);
    }
}

main_activity.xml

<?xml version="1.0" encoding="utf-8"?>
<FrameLayout  xmlns:android="http://schemas.android.com/apk/res/android"
    android:id="@+id/main_content"
    android:layout_width="match_parent"
    android:layout_height="match_parent" />

我不得不克隆ConstraintSet。不仅如此，克隆还必须在添加视图后进行。添加视图并克隆ConstraintSet后，它知道视图的大小并可以相应地设置约束

private FormViewBuilder(Context context) {
    this.context = context;
    formView = new FormView(context); // initialize
    // ...
}

// ...

public FormViewBuilder addField(int id, @NonNull String key, @NonNull String hint, String requiredMessage) {
    TextInputLayout field = newTextField(context, id, key, hint, requiredMessage);
    getLastRow().add(field);

    // add views before build <<================ important
    ConstraintLayout.LayoutParams params = new ConstraintLayout.LayoutParams(
            ConstraintLayout.LayoutParams.CHAIN_SPREAD,
            ConstraintLayout.LayoutParams.WRAP_CONTENT
    );
    formView.addView(field, params);

    return this;
}


public FormView build() {
    ConstraintSet constraints = new ConstraintSet();
    constraints.clone(formView); // clone after views are added <<================ important

    // only set constraints. do not add or remove views

    constraints.applyTo(formView);
    return formView;
}

---

万一有人无意中发现了这一点，另一种可能是您使用了错误的LayoutParams类型。确保使用布局的确切类型的LayoutParams子类，在本例中为：ConstraintLayout.LayoutParams.WRAP_CONTENT

private FormViewBuilder(Context context) {
    this.context = context;
    formView = new FormView(context); // initialize
    // ...
}

// ...

public FormViewBuilder addField(int id, @NonNull String key, @NonNull String hint, String requiredMessage) {
    TextInputLayout field = newTextField(context, id, key, hint, requiredMessage);
    getLastRow().add(field);

    // add views before build <<================ important
    ConstraintLayout.LayoutParams params = new ConstraintLayout.LayoutParams(
            ConstraintLayout.LayoutParams.CHAIN_SPREAD,
            ConstraintLayout.LayoutParams.WRAP_CONTENT
    );
    formView.addView(field, params);

    return this;
}


public FormView build() {
    ConstraintSet constraints = new ConstraintSet();
    constraints.clone(formView); // clone after views are added <<================ important

    // only set constraints. do not add or remove views

    constraints.applyTo(formView);
    return formView;
}