BaselineLayout.java revision 583f64754e19245bf81e8a23e87b4c03dc475786 
1/*
2 * Copyright (C) 2016 The Android Open Source Project
3 *
4 * Licensed under the Apache License, Version 2.0 (the "License");
5 * you may not use this file except in compliance with the License.
6 * You may obtain a copy of the License at
7 *
8 *      http://www.apache.org/licenses/LICENSE-2.0
9 *
10 * Unless required by applicable law or agreed to in writing, software
11 * distributed under the License is distributed on an "AS IS" BASIS,
12 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
13 * See the License for the specific language governing permissions and
14 * limitations under the License.
15 */
16
17package android.support.design.internal;
18
19import android.content.Context;
20import android.support.v4.view.ViewCompat;
21import android.support.v7.widget.ViewUtils;
22import android.util.AttributeSet;
23import android.view.View;
24import android.view.ViewGroup;
25
26/**
27 * A simple ViewGroup that aligns all the views inside on a baseline. Note: bottom padding for this
28 * view will be measured starting from the baseline.
29 *
30 * @hide
31 */
32public class BaselineLayout extends ViewGroup {
33    private int mBaseline = -1;
34
35    public BaselineLayout(Context context) {
36        super(context, null, 0);
37    }
38
39    public BaselineLayout(Context context, AttributeSet attrs) {
40        super(context, attrs, 0);
41    }
42
43    public BaselineLayout(Context context, AttributeSet attrs, int defStyleAttr) {
44        super(context, attrs, defStyleAttr);
45    }
46
47    protected void onMeasure(int widthMeasureSpec, int heightMeasureSpec) {
48        final int count = getChildCount();
49        int maxWidth = 0;
50        int maxHeight = 0;
51        int maxChildBaseline = -1;
52        int maxChildDescent = -1;
53        int childState = 0;
54
55        for (int i = 0; i < count; i++) {
56            final View child = getChildAt(i);
57            if (child.getVisibility() == GONE) {
58                continue;
59            }
60
61            measureChild(child, widthMeasureSpec, heightMeasureSpec);
62            final int baseline = child.getBaseline();
63            if (baseline != -1) {
64                maxChildBaseline = Math.max(maxChildBaseline, baseline);
65                maxChildDescent = Math.max(maxChildDescent, child.getMeasuredHeight() - baseline);
66            }
67            maxWidth = Math.max(maxWidth, child.getMeasuredWidth());
68            maxHeight = Math.max(maxHeight, child.getMeasuredHeight());
69            childState = ViewUtils.combineMeasuredStates(childState,
70                    ViewCompat.getMeasuredState(child));
71        }
72        if (maxChildBaseline != -1) {
73            maxChildDescent = Math.max(maxChildDescent, getPaddingBottom());
74            maxHeight = Math.max(maxHeight, maxChildBaseline + maxChildDescent);
75            mBaseline = maxChildBaseline;
76        }
77        maxHeight = Math.max(maxHeight, getSuggestedMinimumHeight());
78        maxWidth = Math.max(maxWidth, getSuggestedMinimumWidth());
79        setMeasuredDimension(
80                ViewCompat.resolveSizeAndState(maxWidth, widthMeasureSpec, childState),
81                ViewCompat.resolveSizeAndState(maxHeight, heightMeasureSpec,
82                        childState << MEASURED_HEIGHT_STATE_SHIFT));
83    }
84
85    @Override
86    protected void onLayout(boolean changed, int left, int top, int right, int bottom) {
87        final int count = getChildCount();
88        final int parentLeft = getPaddingLeft();
89        final int parentRight = right - left - getPaddingRight();
90        final int parentContentWidth = parentRight - parentLeft;
91        final int parentTop = getPaddingTop();
92
93        for (int i = 0; i < count; i++) {
94            final View child = getChildAt(i);
95            if (child.getVisibility() == GONE) {
96                continue;
97            }
98
99            final int width = child.getMeasuredWidth();
100            final int height = child.getMeasuredHeight();
101
102            final int childLeft = parentLeft + (parentContentWidth - width) / 2;
103            final int childTop;
104            if (mBaseline != -1 && child.getBaseline() != -1) {
105                childTop = parentTop + mBaseline - child.getBaseline();
106            } else {
107                childTop = parentTop;
108            }
109
110            child.layout(childLeft, childTop, childLeft + width, childTop + height);
111        }
112    }
113
114    @Override
115    public int getBaseline() {
116        return mBaseline;
117    }
118}
119