Android TextView 文本展开收起

在界面上需要展示一个TextView，默认超过4行则在末尾添加"展开"，用户点击展开文本后则完整显示文本，同时末尾添加“收起”。

先列出TextView的布局

 <TextView
     android:id="@+id/content"
     android:layout_width="match_parent"
     android:layout_height="wrap_content"
     android:layout_marginStart="20dp"
     android:layout_marginEnd="20dp"
     android:textColor="#666666"
     android:lineSpacingExtra="3dp"
     android:textSize="13sp"
     />

由于我们需要根据文本是否达到4行来做对应展示，很自然的想到要在TextView布局完成之后再处理，此处设置onPreDrawListener

contentTextView.getViewTreeObserver()
               .addOnPreDrawListener(new ViewTreeObserver.OnPreDrawListener() {
                   @Override
                   public boolean onPreDraw() {

                       contentTextView.getViewTreeObserver().removeOnPreDrawListener(this);

                       expandText();
                       return false;
                   }
               });

在expandText中，如果文本布局超过4行，我们需要截取第四行，在文本后面预留展开的位置，最后通过设置span添加点击事件，收起功能类似。

    String expand = "[展开]";
    String collapse = "[收起]";

    private void expandText() {

        CharSequence text = contentTextView.getText();

        int width = contentTextView.getWidth();
        TextPaint paint = contentTextView.getPaint();
        Layout layout = contentTextView.getLayout();
        int line = layout.getLineCount();
        if (line > 4) {
            int start = layout.getLineStart(3);
            int end = layout.getLineVisibleEnd(3);
            CharSequence lastLine = text.subSequence(start, end);

            float expandWidth = paint.measureText(expand);
            float remain = width - expandWidth;

            CharSequence ellipsize =
                    TextUtils.ellipsize(lastLine,
                                        paint,
                                        remain,
                                        TextUtils.TruncateAt.END);

            ClickableSpan clickableSpan = new ClickableSpan() {

                @Override
                public void onClick(@NonNull View widget) {

                    collapseText();
                }
            };

            SpannableStringBuilder ssb = new SpannableStringBuilder();
            ssb.append(text.subSequence(0, start));
            ssb.append(ellipsize);
            ssb.append(expand);
            ssb.setSpan(new ForegroundColorSpan(0xFF7369F8),
                        ssb.length() - expand.length(), ssb.length(),
                        Spanned.SPAN_INCLUSIVE_EXCLUSIVE);
            ssb.setSpan(clickableSpan,
                        ssb.length() - expand.length(), ssb.length(),
                        Spanned.SPAN_INCLUSIVE_EXCLUSIVE);
            contentTextView.setMovementMethod(LinkMovementMethod.getInstance());
            contentTextView.setText(ssb);
        }
    }

    private void collapseText() {

        // 默认此时文本肯定超过行数了，直接在最后拼接文本
        ClickableSpan clickableSpan = new ClickableSpan() {

            @Override
            public void onClick(@NonNull View widget) {

                expandText();
            }
        };

        SpannableStringBuilder ssb = new SpannableStringBuilder();
        ssb.append(bean.getMsg());
        ssb.append(collapse);
        ssb.setSpan(new ForegroundColorSpan(0xFF7369F8),
                    ssb.length() - collapse.length(), ssb.length(),
                    Spanned.SPAN_INCLUSIVE_EXCLUSIVE);
        ssb.setSpan(clickableSpan,
                    ssb.length() - collapse.length(), ssb.length(),
                    Spanned.SPAN_INCLUSIVE_EXCLUSIVE);
        contentTextView.setText(ssb);
    }