如何以编程方式访问 ConstraintLayout 中视图的当前约束？

Question

我可以使用 ConstraintSet 以编程方式修改 ConstraintLayout 中视图的约束，但在应用修改之前，我想测试它是否已经完成。为此，我需要以编程方式访问 ConstraintLayout 中视图的当前约束。

例如，这里我想移除 TextView 'title' 顶部和 TextView 视图 'subtitle' 底部之间的约束。然后将 TextView 'title' 的顶部约束到 'videoView' 的底部。但首先我需要检查 TextView 'title' 是否已经被限制在 'videoView' 的底部（代码从 android's official website 修改）。注意，我不能在这个网站上插入 HTML 的最后一行，它是 /android.support.constraint.ConstraintLayout 在尖括号中。

public class MainActivity extends AppCompatActivity {
ConstraintSet mConstraintSet = new ConstraintSet(); // create a Constraint Set
ConstraintLayout mConstraintLayout; // cache the ConstraintLayout

@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_main);
    mConstraintLayout = (ConstraintLayout) findViewById(R.id.root);
    mConstraintSet.clone(mConstraintLayout); // get constraints from ConstraintSet
}

public void userDoesSomething(View v) {
    //test if title has already been constrained to bottom of videoView
    if (mConstraintLayout 'TITLE' IS NOT CONSTRAINED TO THE BOTTOM OF 'VIDEOVIEW'){
        mConstraintSet.connect(R.id.Title, ConstraintSet.TOP, R.id.videoView, ConstraintSet.BOTTOM); // set new constraints to ConstraintSet
        mConstraintSet.applyTo(mConstraintLayout); // set new constraints to ConstraintLayout
    }
}

}

<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/root"
android:layout_width="match_parent"
android:layout_height="match_parent"
tools:context="com.example.test.MainActivity"
android:orientation="vertical">

<VideoView
    android:id="@+id/videoView"
    android:layout_width="match_parent"
    android:layout_height="100dp"
    app:layout_constraintTop_toTopOf="parent"
    app:layout_constraintLeft_toLeftOf="parent"

    />

<TextView
    android:id="@+id/subtitiles"
    android:layout_width="match_parent"
    android:layout_height="wrap_content"
    app:layout_constraintTop_toBottomOf="@+id/videoView"
    app:layout_constraintLeft_toLeftOf="parent"
    android:gravity="center"
    android:text="The problem with this pond is that there are too many toads"
    android:textSize="25sp"
    android:background="@android:color/white"

    />

<TextView
    android:id="@+id/title"
    android:layout_width="match_parent"
    android:layout_height="wrap_content"
    app:layout_constraintTop_toBottomOf="@+id/subtitiles"
    app:layout_constraintLeft_toLeftOf="parent"
    android:gravity="center"
    android:text="Toad"
    android:textSize="25sp"
    android:background="@android:color/white"
    />

Answer 1

据我所知，没有办法，但是您可以尝试比较两个 ConstraintLayout.LayoutParams，例如：

public class MainActivity extends AppCompatActivity {
ConstraintSet mConstraintSet = new ConstraintSet(); // create a Constraint Set
ConstraintLayout mConstraintLayout; // cache the ConstraintLayout

int mConstraintValue;
TextView mTextView;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        mConstraintLayout = (ConstraintLayout) findViewById(R.id.root);
        mTextView = (TextView) findViewById(R.id.title);
        mConstraintSet.clone(mConstraintLayout); // get constraints from ConstraintSet
        ConstraintLayout.LayoutParams params = (ConstraintLayout.LayoutParams) mTextView.getLayoutParams();
        mConstraintValue = params.topToBottom;
    }

    public void userDoesSomething(View v) {
        //test if title has already been constrained to bottom of videoView
         ConstraintLayout.LayoutParams params = (ConstraintLayout.LayoutParams) mTextView.getLayoutParams();
        if (mConstraintValue.equals(params.topToBottom)){
            mConstraintSet.connect(R.id.Title, ConstraintSet.TOP, R.id.videoView, ConstraintSet.BOTTOM); // set new constraints to ConstraintSet
            mConstraintSet.applyTo(mConstraintLayout); // set new constraints to ConstraintLayout
        }
    }
}

希望这会有所帮助。