https://cells-source.cs.columbia.edu/plugins/gitiles/platform/packages/apps/Calendar/+/android-4.2.2_r1.2/res/layout/expandable_textview.xml

expandable_textview.xml

<?xml version="1.0" encoding="utf-8"?>
<!-- Copyright (C) 2011 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.
-->
<com.android.calendar.ExpandableTextView
    xmlns:android="http://schemas.android.com/apk/res/android"
    android:layout_width="match_parent"
    android:layout_height="wrap_content"
    android:layout_marginTop="8dip"
    android:layout_marginLeft="@dimen/event_info_desc_margin_left"
    android:visibility="gone"
    android:orientation="vertical" >
 
    <TextView
        android:id="@+id/expandable_text"
        style="?android:attr/textAppearanceSmall"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:layout_marginRight="@dimen/event_info_desc_margin_right"
        android:autoLink="all"
        android:ellipsize="end"
        android:textIsSelectable="true"
        android:textColor="@color/event_info_description_color"
        android:textSize="@dimen/event_info_text_size" />
 
    <ImageButton
        android:id="@+id/expand_collapse"
        style="?android:attr/textAppearanceSmall"
        android:layout_width="32dip"
        android:layout_height="32dip"
        android:layout_marginBottom="0dip"
        android:paddingRight="0dip"
        android:layout_gravity="right"
        android:gravity="center_vertical|right"
        android:visibility="gone"
        android:src="@drawable/ic_expand_small_holo_light"
        android:background="#00000000"
        android:textColor="@color/event_info_description_color" />
 
</com.android.calendar.ExpandableTextView>

ExpandableTextView.java

/*
 * Copyright (C) 2011 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 com.android.calendar;
 
import android.content.Context;
import android.graphics.drawable.Drawable;
import android.util.AttributeSet;
import android.view.View;
import android.view.View.OnClickListener;
import android.widget.ImageButton;
import android.widget.LinearLayout;
import android.widget.TextView;
 
public class ExpandableTextView extends LinearLayout implements OnClickListener {
 
    TextView mTv;
    ImageButton mButton; // Button to expand/collapse
 
    private boolean mRelayout = false;
    private boolean mCollapsed = true; // Show short version as default.
    private int mMaxCollapsedLines = 8; // The default number of lines;
    private Drawable mExpandDrawable;
    private Drawable mCollapseDrawable;
 
    public ExpandableTextView(Context context) {
        super(context);
        init();
    }
 
    public ExpandableTextView(Context context, AttributeSet attrs) {
        super(context, attrs, 0);
        init();
    }
 
    public ExpandableTextView(Context context, AttributeSet attrs, int defStyle) {
        super(context, attrs, defStyle);
        init();
    }
 
    void init() {
        mMaxCollapsedLines = getResources().getInteger((R.integer.event_info_desc_line_num));
        mExpandDrawable = getResources().getDrawable(R.drawable.ic_expand_small_holo_light);
        mCollapseDrawable = getResources().getDrawable(R.drawable.ic_collapse_small_holo_light);
    }
 
    @Override
    public void onClick(View v) {
        if (mButton.getVisibility() != View.VISIBLE) {
            return;
        }
 
        mCollapsed = !mCollapsed;
        mButton.setImageDrawable(mCollapsed ? mExpandDrawable : mCollapseDrawable);
        mTv.setMaxLines(mCollapsed ? mMaxCollapsedLines : Integer.MAX_VALUE);
    }
 
    @Override
    protected void onMeasure(int widthMeasureSpec, int heightMeasureSpec) {
        // If no change, measure and return
        if (!mRelayout || getVisibility() == View.GONE) {
            super.onMeasure(widthMeasureSpec, heightMeasureSpec);
            return;
        }
        mRelayout = false;
 
        // Setup with optimistic case
        // i.e. Everything fits. No button needed
        mButton.setVisibility(View.GONE);
        mTv.setMaxLines(Integer.MAX_VALUE);
 
        // Measure
        super.onMeasure(widthMeasureSpec, heightMeasureSpec);
 
        // If the text fits in collapsed mode, we are done.
        if (mTv.getLineCount() <= mMaxCollapsedLines) {
            return;
        }
 
        // Doesn't fit in collapsed mode. Collapse text view as needed. Show
        // button.
        if (mCollapsed) {
            mTv.setMaxLines(mMaxCollapsedLines);
        }
        mButton.setVisibility(View.VISIBLE);
 
        // Re-measure with new setup
        super.onMeasure(widthMeasureSpec, heightMeasureSpec);
    }
 
    private void findViews() {
        mTv = (TextView) findViewById(R.id.expandable_text);
        mTv.setOnClickListener(this);
        mButton = (ImageButton) findViewById(R.id.expand_collapse);
        mButton.setOnClickListener(this);
    }
 
    public void setText(String text) {
        mRelayout = true;
        if (mTv == null) {
            findViews();
        }
        String trimmedText = text.trim();
        mTv.setText(trimmedText);
        this.setVisibility(trimmedText.length() == 0 ? View.GONE : View.VISIBLE);
    }
 
    public CharSequence getText() {
        if (mTv == null) {
            return "";
        }
        return mTv.getText();
    }
}