Android TextView仿微信可折叠效果

import android.content.Context;
import android.content.res.TypedArray;
import android.util.AttributeSet;
import android.view.LayoutInflater;
import android.view.MotionEvent;
import android.view.View;
import android.view.ViewTreeObserver;
import android.widget.LinearLayout;
import android.widget.TextView;
/**
 * 可折叠的textview
 */
public class ExpandTextView extends LinearLayout {
  public static final int DEFAULT_MAX_LINES = 3;
  private TextView contentText;
  private TextView textPlus;
  private int showLines;
  private ExpandStatusListener expandStatusListener;
  private boolean isExpand;

  public ExpandTextView(Context context) {
    super(context);
    initView();
  }

  public ExpandTextView(Context context, AttributeSet attrs) {
    super(context, attrs);
    initAttrs(attrs);
    initView();
  }

  public ExpandTextView(Context context, AttributeSet attrs, int defStyleAttr) {
    super(context, attrs, defStyleAttr);
    initAttrs(attrs);
    initView();
  }

  private void initAttrs(AttributeSet attrs) {
    TypedArray typedArray = getContext().getTheme().obtainStyledAttributes(attrs, R.styleable.ExpandTextView, 0, 0);
    try {
      showLines = typedArray.getInt(R.styleable.ExpandTextView_showLines, DEFAULT_MAX_LINES);
    }finally {
      typedArray.recycle();
    }
  }

  private void initView() {
    setOrientation(LinearLayout.VERTICAL);
    LayoutInflater.from(getContext()).inflate(R.layout.layout_magic_text, this);
    contentText = (TextView) findViewById(R.id.contentText);
    if(showLines > 0){
      contentText.setMaxLines(showLines);
    }

    textPlus = (TextView) findViewById(R.id.textPlus);
    textPlus.setOnClickListener(new OnClickListener() {
      @Override
      public void onClick(View view) {
        String textStr = textPlus.getText().toString().trim();
        if("全文".equals(textStr)){
          contentText.setMaxLines(Integer.MAX_VALUE);
          textPlus.setText("收起");
          setExpand(true);
        }else{
          contentText.setMaxLines(showLines);
          textPlus.setText("全文");
          setExpand(false);
        }
        //通知外部状态已变更
        if(expandStatusListener != null){
          expandStatusListener.statusChange(isExpand());
        }
      }
    });
  }

  public void setText(final CharSequence content){

    //在开始绘制contentText内容时，进行监听
    contentText.getViewTreeObserver().addOnPreDrawListener(new ViewTreeObserver.OnPreDrawListener() {

      @Override
      public boolean onPreDraw() {
        // 避免重复监听
        contentText.getViewTreeObserver().removeOnPreDrawListener(this);
        //获取当前文本的行数
        int linCount = contentText.getLineCount();
        if(linCount > showLines){

          if(isExpand){
            contentText.setMaxLines(Integer.MAX_VALUE);
            textPlus.setText("收起");
          }else{
            contentText.setMaxLines(showLines);
            textPlus.setText("全文");
          }
          textPlus.setVisibility(View.VISIBLE);
        }else{
          textPlus.setVisibility(View.GONE);
        }
        return true;
      }


    });
    contentText.setText(content);
  }

  public void setExpand(boolean isExpand){
    this.isExpand = isExpand;
  }

  public boolean isExpand(){
    return this.isExpand;
  }

  public void setExpandStatusListener(ExpandStatusListener listener){
    this.expandStatusListener = listener;
  }

  public interface ExpandStatusListener{
    void statusChange(boolean isExpand);
  }

  @Override
  public boolean onTouchEvent(MotionEvent event) {
    return textPlus.dispatchTouchEvent(event);
  }
}

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
       android:layout_width="match_parent"
       android:layout_height="match_parent"
       android:orientation="vertical">

  <TextView
    android:id="@+id/contentText"
    android:textSize="18sp"
    android:textColor="#000000"
    android:layout_width="match_parent"
    android:layout_height="wrap_content"
    android:text=""/>

  <TextView
    android:id="@+id/textPlus"
    android:textSize="18sp"
    android:textColor="#666666"
    android:layout_width="match_parent"
    android:layout_height="wrap_content"
    android:layout_marginTop="15dp"
    android:text=""/>

</LinearLayout>

<declare-styleable name="ExpandTextView">
    <attr name="showLines" format="integer"/>
</declare-styleable>

<mo.yumf.com.myviews.ExpandTextView
    android:id="@+id/expandTextView"
    android:layout_width="match_parent"
    android:layout_height="wrap_content"
    app:showLines="4"/>