assistant-android/app/src/main/java/com/gh/common/view/ExpandTextView.java

package com.gh.common.view;

import android.content.Context;
import android.content.res.TypedArray;
import android.os.Build;
import android.text.Layout;
import android.text.SpannableStringBuilder;
import android.text.Spanned;
import android.text.TextPaint;
import android.text.style.ClickableSpan;
import android.util.AttributeSet;
import android.view.View;

import com.gh.common.util.DisplayUtils;
import com.gh.gamecenter.R;

import androidx.appcompat.widget.AppCompatTextView;
import androidx.core.content.ContextCompat;

public class ExpandTextView extends AppCompatTextView {

    private CharSequence mSnapshotText;

    private String mEndText = "...";
    private String mExpandText = mEndText + "全文";
    private boolean mUseGradientAlphaEndText = false;

    private int mMaxLines = 3; // 由于sdk版本限制(getMaxLines) 这里设置默认值

    private static int DEFAULT_ADDITIONAL_END_TEXT_COUNT = 2;

    private boolean mInitLayout = false;
    private boolean mIsExpanded = false; // 位于 recyclerView 时需要自行在外层管理是否已展开

    private ExpandCallback mExpandCallback;

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

    public ExpandTextView(Context context, AttributeSet attrs) {
        super(context, attrs);
        if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.JELLY_BEAN) {
            mMaxLines = getMaxLines();
        }
        TypedArray ta = context.obtainStyledAttributes(attrs, R.styleable.ExpandTextView);
        mUseGradientAlphaEndText = ta.getBoolean(R.styleable.ExpandTextView_useGradientAlphaEndText, false);
        mEndText = ta.getString(R.styleable.ExpandTextView_endText) == null ? mEndText : ta.getString(R.styleable.ExpandTextView_endText);
        mExpandText = ta.getString(R.styleable.ExpandTextView_expandText) == null ? mExpandText : ta.getString(R.styleable.ExpandTextView_expandText);
        ta.recycle();
    }

    @Override
    protected void onLayout(boolean changed, int left, int top, int right, int bottom) {
        super.onLayout(changed, left, top, right, bottom);
        if (mInitLayout && !mIsExpanded && getLineCount() > mMaxLines) {
            mSnapshotText = getText();
            mInitLayout = false;
            showExpandButton();
        }
    }

    public void setExpendText(String text) {
        this.mExpandText = text;
    }

    public void setExpandCallback(ExpandCallback callback) {
        this.mExpandCallback = callback;
    }

    @Override
    public void setText(CharSequence text, BufferType type) {
        mInitLayout = true;
        super.setText(text, type);
    }

    private void showExpandButton() {
        String finalEndText = "";

        Layout layout = getLayout();
        int start = layout.getLineStart(0);
        int lastLineEnd = layout.getLineEnd(mMaxLines - 1);
        int lastLineStart = layout.getLineStart(mMaxLines - 1);
        float lastLineRight = layout.getLineRight(mMaxLines - 1);

        int viewWidth = getWidth() - getPaddingRight() - getPaddingLeft();
        int additionalEndTextCount = 0;

        TextPaint paint = getPaint();
        float expandTextWidth;
        if (mUseGradientAlphaEndText) {
            additionalEndTextCount = DEFAULT_ADDITIONAL_END_TEXT_COUNT;
            // 如果不加多个括号的话有可能算不对，惊了，明明是同样的 paint 同样的文字，长度却会略有不同
            expandTextWidth = paint.measureText(mEndText + mExpandText + " ");
        } else {
            expandTextWidth = paint.measureText(mExpandText);
        }

        CharSequence content = mSnapshotText.subSequence(start, lastLineEnd);

        if (viewWidth - lastLineRight > expandTextWidth) {
            if (mUseGradientAlphaEndText) {
                finalEndText = content.toString().substring(content.length() - additionalEndTextCount, content.length()) + mEndText;
                finalEndText = finalEndText.replace("\n", "");

                content = content.subSequence(0, content.length() - additionalEndTextCount) + finalEndText + mExpandText;
            } else {
                content = content.toString().trim() + mExpandText;
            }
        } else {
            CharSequence lastText = mSnapshotText.subSequence(lastLineStart, lastLineEnd);
            for (int i = lastText.length() - 1; i > 0; i--) {
                CharSequence sequence = lastText.subSequence(0, i);
                float w = paint.measureText(sequence.toString());
                if (viewWidth - w - DisplayUtils.dip2px(5) > expandTextWidth) {
                    if (mUseGradientAlphaEndText) {
                        finalEndText = lastText.subSequence(i - additionalEndTextCount, i) + mEndText;
                        finalEndText = finalEndText.replace("\n", "");

                        content = mSnapshotText.subSequence(start, lastLineStart + i - additionalEndTextCount) + finalEndText + mExpandText;
                    } else {
                        content = mSnapshotText.subSequence(start, lastLineStart + i) + mExpandText;
                    }
                    break;
                }
            }
        }

        SpannableStringBuilder msp = new SpannableStringBuilder(mSnapshotText);
        int length = msp.length();
        int startPosition = 0;
        startPosition = content.length() - finalEndText.length() - mExpandText.length();
        startPosition = Math.max(startPosition, 0);

        // 避免越界
        if (startPosition >= length) return;

        msp.replace(startPosition, length, finalEndText + mExpandText);

        msp.setSpan(new ClickableSpan() {
            @Override
            public void updateDrawState(TextPaint ds) {
                super.updateDrawState(ds);
                ds.setColor(ContextCompat.getColor(getContext(), R.color.theme_font));
                ds.setUnderlineText(false);
            }

            @Override
            public void onClick(View widget) {
                mIsExpanded = true;
                setMaxLines(Integer.MAX_VALUE);
                setText(mSnapshotText);

                if (mExpandCallback != null) {
                    mExpandCallback.onExpand();
                }
            }
        }, startPosition + mEndText.length(), msp.length(), Spanned.SPAN_EXCLUSIVE_EXCLUSIVE);
        msp.setSpan(new GradientAlphaTextSpan(), startPosition, startPosition + finalEndText.length(), Spanned.SPAN_EXCLUSIVE_EXCLUSIVE);

        setText(msp);
        setMovementMethod(CustomLinkMovementMethod.getInstance());
    }

    /**
     * 此方法仅更改标记，不做实际展开的操作
     */
    public void setIsExpanded(boolean isExpanded) {
        mIsExpanded = isExpanded;
    }

    public void setExpandMaxLines(int maxLines) {
        mMaxLines = maxLines;
        setMaxLines(maxLines);
    }

    public interface ExpandCallback {
        void onExpand();
    }

}