Placeholder.java
/*
* Copyright (C) 2021 The Android Open Source Project
*
* Licensed under the Apache License, Version 2.0 (the "License");
* you may not use this file except in compliance with the License.
* You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*/
package androidx.constraintlayout.core.widgets;
import static androidx.constraintlayout.core.widgets.analyzer.BasicMeasure.AT_MOST;
import static androidx.constraintlayout.core.widgets.analyzer.BasicMeasure.EXACTLY;
import static androidx.constraintlayout.core.widgets.analyzer.BasicMeasure.UNSPECIFIED;
import androidx.constraintlayout.core.LinearSystem;
/**
* Simple VirtualLayout that center the first referenced widget onto itself.
*/
public class Placeholder extends VirtualLayout {
/**
* @TODO: add description
*/
public void measure(int widthMode, int widthSize, int heightMode, int heightSize) {
int width = 0;
int height = 0;
int paddingLeft = getPaddingLeft();
int paddingRight = getPaddingRight();
int paddingTop = getPaddingTop();
int paddingBottom = getPaddingBottom();
width += paddingLeft + paddingRight;
height += paddingTop + paddingBottom;
if (mWidgetsCount > 0) {
// grab the first referenced widget size in case we are ourselves in wrap_content
width += mWidgets[0].getWidth();
height += mWidgets[0].getHeight();
}
width = Math.max(getMinWidth(), width);
height = Math.max(getMinHeight(), height);
int measuredWidth = 0;
int measuredHeight = 0;
if (widthMode == EXACTLY) {
measuredWidth = widthSize;
} else if (widthMode == AT_MOST) {
measuredWidth = Math.min(width, widthSize);
} else if (widthMode == UNSPECIFIED) {
measuredWidth = width;
}
if (heightMode == EXACTLY) {
measuredHeight = heightSize;
} else if (heightMode == AT_MOST) {
measuredHeight = Math.min(height, heightSize);
} else if (heightMode == UNSPECIFIED) {
measuredHeight = height;
}
setMeasure(measuredWidth, measuredHeight);
setWidth(measuredWidth);
setHeight(measuredHeight);
needsCallbackFromSolver(mWidgetsCount > 0);
}
@Override
public void addToSolver(LinearSystem system, boolean optimize) {
super.addToSolver(system, optimize);
if (mWidgetsCount > 0) {
ConstraintWidget widget = mWidgets[0];
widget.resetAllConstraints();
widget.connect(ConstraintAnchor.Type.LEFT, this, ConstraintAnchor.Type.LEFT);
widget.connect(ConstraintAnchor.Type.RIGHT, this, ConstraintAnchor.Type.RIGHT);
widget.connect(ConstraintAnchor.Type.TOP, this, ConstraintAnchor.Type.TOP);
widget.connect(ConstraintAnchor.Type.BOTTOM, this, ConstraintAnchor.Type.BOTTOM);
}
}
}