使用 ConstraintSet 时测量的布局大小为零

Posted 2023-03-17

【中文标题】使用 ConstraintSet 时测量的布局大小为零

【英文标题】：measured layout size is zero when using ConstraintSet

【发布时间】：2019-04-13 15:09:46

【问题描述】：

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。

我对所有孩子和父母都试过requestLayout、forceLayout、invalidate。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;
    

---

MainActivity.java

public class MainActivity extends AppCompatActivity 

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

        FormView form = FormBuilder.newForm(this)
                .addField("First name").addField("Last name")
                .nextRow()
                .addField("Phone numnber")
                .build();

        FrameLayout layout = findViewById(R.id.main_content);
        FrameLayout.LayoutParams params = new FrameLayout.LayoutParams(
                FrameLayout.LayoutParams.MATCH_PARENT,
                FrameLayout.LayoutParams.WRAP_CONTENT
        );
        layout.addView(form, params);
    

---

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_
    android:layout_ />

【参考方案1】：

我不得不克隆ConstraintSet。不仅如此，还必须在添加视图之后 进行克隆。添加视图并克隆ConstraintSet后，它会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;

【参考方案2】：

万一有人偶然发现这一点，另一种可能性是您使用了错误的 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。