大家可能都會遇到這樣一個設計：某個界面設計有個ShowMore按鈕，點擊是文本的展開與收縮。Android默認的效果大家可能都會通過setMaxLines來實現，但直接這么做是沒有動畫的，就是一個文本的突變。很早之前也想過要實現一個動畫，但對TextView的Layout不熟悉就一直沒做過。最近在一次CodeReview的時候，iOS實現了這個效果，這不行啊，我們Android不能落后啊。所以最后作出了下面的效果。

textview_show_more_with_animation.gif

基本是完整兼容TextView本身。收縮小圖有...，而且這個點點還是TextView本身的實現，沒做過任何修改。

不關心原理可以直接使用TextViewUtils
https://github.com/aesean/ActivityStack/blob/master/app/src/main/java/com/aesean/activitystack/utils/TextViewUtils.java
使用方法很簡單：

  int lines = mTextView.getMaxLines() == 3 ? Integer.MAX_VALUE : 3;
  mTextView.setMaxLineWithAnimation(lines);

但其實比起代碼本身來說，實現代碼的過程更加重要。

AutoSizeTextView

第一次看到這個效果的話，我們先思考下，如何實現這個效果？但就動畫來說就是TextView的高度從3行的高度變到了最大行的高度。如果我們能拿到這兩個高度的話，結合ValueAnimator應該大致可以做到這個效果。那問題來了怎么拿到3行或者多行的文字高度？拿View本身的高度嗎？那就麻煩了，那樣必須先繪制View然后才能拿到，但我們顯然是想要在設置前就知道這個高度的。麻煩了，簡單看下TextView實現會發現，TextView會通過Layout來測量文本位置，代碼非常復雜。我不是很熟悉TextView的繪制和Layout。所以雖然簡單瀏覽了還是對測量TextView高度毫無頭緒。

怎么辦？不知道有沒有人知道，Android O時候Google讓TextView實現了類似iOS上的自動改變文字大小的功能。
https://developer.android.com/guide/topics/ui/look-and-feel/autosizing-textview.html
看到這個有沒有什么靈感？雖然沒有看過具體實現，但猜測這里的AutoSize，應該是需要對文本進行測量的，不斷用不同字號，對文本進行測量，直到測量到合適的字號，然后設置。
猜測歸猜測，我們實際去看下具體實現。不用想具體實現應該在AppCompatTextView類中。
然后很容易找到三個setAutoSizeText開頭的方法和一個AppCompatTextHelper

private final AppCompatTextHelper mTextHelper;
public void setAutoSizeTextTypeWithDefaults
public void setAutoSizeTextTypeUniformWithConfiguration
public void setAutoSizeTextTypeUniformWithPresetSizes

這三個方法都是調用類AppCompatTextHelper中對應的方法。跟到AppCompatTextHelper很容易就找到了AppCompatTextViewAutoSizeHelper

class AppCompatTextHelper {
    private final @NonNull AppCompatTextViewAutoSizeHelper mAutoSizeTextHelper;

大致瀏覽下這個類會發現這樣一個方法

     /**
     * Automatically computes and sets the text size.
     *
     * @hide
     */
    @RestrictTo(LIBRARY_GROUP)
    void autoSizeText() {
        if (!isAutoSizeEnabled()) {
            return;
        }

        if (mNeedsAutoSizeText) {
            if (mTextView.getMeasuredHeight() <= 0 || mTextView.getMeasuredWidth() <= 0) {
                return;
            }

            final boolean horizontallyScrolling = invokeAndReturnWithDefault(
                    mTextView, "getHorizontallyScrolling", false);
            final int availableWidth = horizontallyScrolling
                    ? VERY_WIDE
                    : mTextView.getMeasuredWidth() - mTextView.getTotalPaddingLeft()
                            - mTextView.getTotalPaddingRight();
            final int availableHeight = mTextView.getHeight() - mTextView.getCompoundPaddingBottom()
                    - mTextView.getCompoundPaddingTop();

            if (availableWidth <= 0 || availableHeight <= 0) {
                return;
            }

            synchronized (TEMP_RECTF) {
                TEMP_RECTF.setEmpty();
                TEMP_RECTF.right = availableWidth;
                TEMP_RECTF.bottom = availableHeight;
                final float optimalTextSize = findLargestTextSizeWhichFits(TEMP_RECTF);
                if (optimalTextSize != mTextView.getTextSize()) {
                    setTextSizeInternal(TypedValue.COMPLEX_UNIT_PX, optimalTextSize);
                }
            }
        }
        // Always try to auto-size if enabled. Functions that do not want to trigger auto-sizing
        // after the next layout pass should set this to false.
        mNeedsAutoSizeText = true;
    }

自動計算和設置文本大小。看到findLargestTextSizeWhichFits這個方法了嗎？

    /**
     * Performs a binary search to find the largest text size that will still fit within the size
     * available to this view.
     */
    private int findLargestTextSizeWhichFits(RectF availableSpace) {
        final int sizesCount = mAutoSizeTextSizesInPx.length;
        if (sizesCount == 0) {
            throw new IllegalStateException("No available text sizes to choose from.");
        }

        int bestSizeIndex = 0;
        int lowIndex = bestSizeIndex + 1;
        int highIndex = sizesCount - 1;
        int sizeToTryIndex;
        while (lowIndex <= highIndex) {
            sizeToTryIndex = (lowIndex + highIndex) / 2;
            if (suggestedSizeFitsInSpace(mAutoSizeTextSizesInPx[sizeToTryIndex], availableSpace)) {
                bestSizeIndex = lowIndex;
                lowIndex = sizeToTryIndex + 1;
            } else {
                highIndex = sizeToTryIndex - 1;
                bestSizeIndex = highIndex;
            }
        }

        return mAutoSizeTextSizesInPx[bestSizeIndex];
    }

大致意思就是二分搜索找到可用的最大文本大小。其實不看注釋，只看方法名字也能明白。方法實現也很簡單，while循環，二分搜索查找合適的大小。


    private boolean suggestedSizeFitsInSpace(int suggestedSizeInPx, RectF availableSpace) {
        final CharSequence text = mTextView.getText();
        final int maxLines = Build.VERSION.SDK_INT >= 16 ? mTextView.getMaxLines() : -1;
        if (mTempTextPaint == null) {
            mTempTextPaint = new TextPaint();
        } else {
            mTempTextPaint.reset();
        }
        mTempTextPaint.set(mTextView.getPaint());
        mTempTextPaint.setTextSize(suggestedSizeInPx);

        // Needs reflection call due to being private.
        Layout.Alignment alignment = invokeAndReturnWithDefault(
                mTextView, "getLayoutAlignment", Layout.Alignment.ALIGN_NORMAL);
        final StaticLayout layout = Build.VERSION.SDK_INT >= 23
                ? createStaticLayoutForMeasuring(
                        text, alignment, Math.round(availableSpace.right), maxLines)
                : createStaticLayoutForMeasuringPre23(
                        text, alignment, Math.round(availableSpace.right));
        // Lines overflow.
        if (maxLines != -1 && (layout.getLineCount() > maxLines
                || (layout.getLineEnd(layout.getLineCount() - 1)) != text.length())) {
            return false;
        }

        // Height overflow.
        if (layout.getHeight() > availableSpace.bottom) {
            return false;
        }

        return true;
    }

通過調用suggestedSizeFitsInSpace方法來判斷大小是否合適，最終找到最合適的大小?？吹街虚g的StaticLayout了嗎？

 final StaticLayout layout = Build.VERSION.SDK_INT >= 23
                ? createStaticLayoutForMeasuring(
                        text, alignment, Math.round(availableSpace.right), maxLines)
                : createStaticLayoutForMeasuringPre23(
                        text, alignment, Math.round(availableSpace.right));

StaticLayout可以用來對文本進行排版測量。這個方法最后很明顯就是通過StaticLayout的測量結果和實際可繪制的大小進行比對來判斷是否合適的。

        // Lines overflow.
        if (maxLines != -1 && (layout.getLineCount() > maxLines
                || (layout.getLineEnd(layout.getLineCount() - 1)) != text.length())) {
            return false;
        }

        // Height overflow.
        if (layout.getHeight() > availableSpace.bottom) {
            return false;
        }

        return true;

OK到這里AutoSizeTextView基本原理就清楚了。那對于我們上面的效果有什么幫助呢？
幫助大了，我們可以順著Google的思路，也創建出一個StaticLayout然后我們就可以自由的計算任意文字在指定TextView上的繪制出的大小了。拿到大小后，動畫就非常簡單了。通過ValueAnimator不斷改變View的heigh來實現展開和收攏動畫。

    @Nullable
    public static ValueAnimator setMaxLinesWithAnimation(@NotNull final TextView textView, final int maxLine) {
        measureTextHeight(textView, textView.getText().toString());

        final int textHeight = measureTextHeight(textView, textView.getText(), maxLine);
        if (textHeight < 0) {
            // measure failed. setMaxLines directly.
            textView.setMaxLines(maxLine);
            return null;
        }
        final int minLines = textView.getMinLines();
        final int targetHeight = textHeight + textView.getCompoundPaddingBottom() + textView.getCompoundPaddingTop();
        return animatorToHeight(textView, targetHeight, new AnimatorListenerAdapter() {
            public void onAnimationStart(Animator animation) {
                super.onAnimationStart(animation);
            }

            public void onAnimationEnd(Animator animation) {
                super.onAnimationEnd(animation);
                textView.setMinLines(minLines);
                textView.setMaxLines(maxLine);
            }
        });
    }

    @Nullable
    public static ValueAnimator animatorToHeight(@NotNull final TextView textView, int h, @Nullable Animator.AnimatorListener listener) {
        final int height = textView.getHeight();
        if (height == h) {
            return null;
        }
        ValueAnimator valueAnimator = new ValueAnimator();
        valueAnimator.setIntValues(height, h);
        long duration = makeDuration(h, height);
        valueAnimator.setDuration(duration);
        valueAnimator.addUpdateListener(new ValueAnimator.AnimatorUpdateListener() {
            @Override
            public void onAnimationUpdate(ValueAnimator animation) {
                int value = (int) animation.getAnimatedValue();
                textView.setHeight(value);
            }
        });
        if (listener != null) {
            valueAnimator.addListener(listener);
        }
        valueAnimator.start();
        return valueAnimator;
    }

但是一定注意在動畫結束后手動恢復MinLines和MaxLines
，不恢復會怎樣呢？這里我就不解釋了，你可以自己實際嘗試下，看會導致什么問題。
最終代碼就是：https://github.com/aesean/ActivityStack/blob/master/app/src/main/java/com/aesean/activitystack/utils/TextViewUtils.java
200多行，不算多。下面代碼和github完全一致方便404用戶。創建StaticLayout部分的代碼都來自AppCompatTextViewAutoSizeHelper，修修補補就變成了下面的類。Google在構建StaticLayout時候反射了部分TextView方法，雖然都在說不推薦反射，但既然Google都用了反射那肯定是有原因的，而且Google用了MethodCacheMap做了Method緩存降低了反射對性能的影響，反射時候用defaultValue來處理反射失敗的情況。你可以嘗試將反射部分的代碼改成下面的代碼來測試反射失敗的情況。

    private static <T> T invokeAndReturnWithDefault(@NonNull Object object, @NonNull final String methodName, @NonNull final T defaultValue) {
        if (1 == 1) {
            return defaultValue;
        }
    }

    @SuppressLint("PrivateApi")
    @Nullable
    private static Method getTextViewMethod(@NonNull final String methodName) {
        if (1 == 1) {
            return null;
        }
    }

import android.animation.Animator;
import android.animation.AnimatorListenerAdapter;
import android.animation.ValueAnimator;
import android.annotation.SuppressLint;
import android.graphics.RectF;
import android.os.Build;
import android.support.annotation.NonNull;
import android.support.annotation.Nullable;
import android.support.annotation.RequiresApi;
import android.text.Layout;
import android.text.StaticLayout;
import android.text.TextDirectionHeuristic;
import android.text.TextDirectionHeuristics;
import android.text.TextPaint;
import android.util.Log;
import android.widget.TextView;

import org.jetbrains.annotations.NotNull;

import java.lang.reflect.Method;
import java.util.Hashtable;

/**
 * TextViewUtils.
 * {@link android.support.v7.widget.AppCompatTextViewAutoSizeHelper}
 *
 * @author danny
 * @version 1.0
 * @since 1/17/18
 */
@RequiresApi(Build.VERSION_CODES.ICE_CREAM_SANDWICH)
public class TextViewUtils {
    private static final String TAG = "TextViewUtils";
    private static Hashtable<String, Method> sTextViewMethodByNameCache = new Hashtable<>();

    private static final long DURATION = 600;       // ms
    private static final long MIN_DURATION = 100;   // ms
    private static final long MAX_DURATION = 1000;  // ms
    private static final long BASE_HEIGHT = 1000;   // px

    // horizontal scrolling is activated.
    private static final int VERY_WIDE = 1024 * 1024;
    private static RectF TEMP_RECT_F = new RectF();
    private static TextPaint sTempTextPaint;

    @Nullable
    public static ValueAnimator setMaxLinesWithAnimation(@NotNull final TextView textView, final int maxLine) {
        measureTextHeight(textView, textView.getText().toString());

        final int textHeight = measureTextHeight(textView, textView.getText(), maxLine);
        if (textHeight < 0) {
            // measure failed. setMaxLines directly.
            textView.setMaxLines(maxLine);
            return null;
        }
        final int minLines = textView.getMinLines();
        final int targetHeight = textHeight + textView.getCompoundPaddingBottom() + textView.getCompoundPaddingTop();
        return animatorToHeight(textView, targetHeight, new AnimatorListenerAdapter() {
            public void onAnimationStart(Animator animation) {
                super.onAnimationStart(animation);
            }

            public void onAnimationEnd(Animator animation) {
                super.onAnimationEnd(animation);
                textView.setMinLines(minLines);
                textView.setMaxLines(maxLine);
            }
        });
    }

    @Nullable
    public static ValueAnimator animatorToHeight(@NotNull final TextView textView, int h, @Nullable Animator.AnimatorListener listener) {
        final int height = textView.getHeight();
        if (height == h) {
            return null;
        }
        ValueAnimator valueAnimator = new ValueAnimator();
        valueAnimator.setIntValues(height, h);
        long duration = makeDuration(h, height);
        valueAnimator.setDuration(duration);
        valueAnimator.addUpdateListener(new ValueAnimator.AnimatorUpdateListener() {
            @Override
            public void onAnimationUpdate(ValueAnimator animation) {
                int value = (int) animation.getAnimatedValue();
                textView.setHeight(value);
            }
        });
        if (listener != null) {
            valueAnimator.addListener(listener);
        }
        valueAnimator.start();
        return valueAnimator;
    }

    private static long makeDuration(int h, int height) {
        long d = (long) (DURATION * (Math.abs(h - height) * 1f / BASE_HEIGHT));
        return Math.max(MIN_DURATION, Math.min(d, MAX_DURATION));
    }

    public static int measureTextHeight(@NotNull TextView textView, @NotNull CharSequence text) {
        return measureTextHeight(textView, text, Build.VERSION.SDK_INT >= Build.VERSION_CODES.JELLY_BEAN ? textView.getMaxLines() : Integer.MAX_VALUE);
    }

    public static int measureTextHeight(@NotNull TextView textView, @NotNull CharSequence text, int maxLines) {
        if (sTempTextPaint == null) {
            sTempTextPaint = new TextPaint();
        }
        sTempTextPaint.set(textView.getPaint());
        sTempTextPaint.setTextSize(textView.getTextSize());

        final int targetHeight = measureTextHeight(textView, text, sTempTextPaint, maxLines);
        sTempTextPaint.reset();
        return targetHeight;
    }

    public static int measureTextHeight(@NotNull TextView textView, @NotNull CharSequence text, @NotNull TextPaint textPaint, int maxLines) {
        final boolean horizontallyScrolling = invokeAndReturnWithDefault(textView, "getHorizontallyScrolling", false);
        final int availableWidth = horizontallyScrolling
                ? VERY_WIDE
                : textView.getMeasuredWidth() - textView.getTotalPaddingLeft()
                - textView.getTotalPaddingRight();
        final int availableHeight = textView.getHeight() - textView.getCompoundPaddingBottom()
                - textView.getCompoundPaddingTop();

        if (availableWidth <= 0 || availableHeight <= 0) {
            return -1;
        }
        TEMP_RECT_F.setEmpty();
        TEMP_RECT_F.right = availableWidth;
        // TEMP_RECT_F.bottom = availableHeight;
        TEMP_RECT_F.bottom = VERY_WIDE;

        // Needs reflection call due to being private.
        Layout.Alignment alignment = invokeAndReturnWithDefault(
                textView, "getLayoutAlignment", Layout.Alignment.ALIGN_NORMAL);
        final StaticLayout layout = createStaticLayoutForMeasuringCompat(text, alignment, Math.round(TEMP_RECT_F.right), Integer.MAX_VALUE, textPaint, textView);
        return layout.getLineTop(Math.min(layout.getLineCount(), maxLines));
    }

    private static StaticLayout createStaticLayoutForMeasuringCompat(CharSequence text, Layout.Alignment alignment, int availableWidth, int maxLines, TextPaint textPaint, TextView textView) {
        if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.M) {
            return createStaticLayoutForMeasuring(text, alignment, availableWidth, maxLines, textPaint, textView);
        } else {
            return createStaticLayoutForMeasuringPre23(text, alignment, availableWidth, textPaint, textView);
        }
    }

    @RequiresApi(Build.VERSION_CODES.M)
    private static StaticLayout createStaticLayoutForMeasuring(CharSequence text, Layout.Alignment alignment, int availableWidth, int maxLines, TextPaint textPaint, TextView textView) {
        // Can use the StaticLayout.Builder (along with TextView params added in or after
        // API 23) to construct the layout.
        final TextDirectionHeuristic textDirectionHeuristic = invokeAndReturnWithDefault(textView, "getTextDirectionHeuristic", TextDirectionHeuristics.FIRSTSTRONG_LTR);

        final StaticLayout.Builder layoutBuilder = StaticLayout.Builder.obtain(text, 0, text.length(), textPaint, availableWidth);

        return layoutBuilder.setAlignment(alignment)
                .setLineSpacing(textView.getLineSpacingExtra(), textView.getLineSpacingMultiplier())
                .setIncludePad(textView.getIncludeFontPadding())
                .setBreakStrategy(textView.getBreakStrategy())
                .setHyphenationFrequency(textView.getHyphenationFrequency())
                .setMaxLines(maxLines == -1 ? Integer.MAX_VALUE : maxLines)
                .setTextDirection(textDirectionHeuristic)
                .build();
    }

    @RequiresApi(Build.VERSION_CODES.ICE_CREAM_SANDWICH)
    private static StaticLayout createStaticLayoutForMeasuringPre23(CharSequence text, Layout.Alignment alignment, int availableWidth, TextPaint textPaint, TextView textView) {
        // Setup defaults.
        float lineSpacingMultiplier = 1.0f;
        float lineSpacingAdd = 0.0f;
        boolean includePad = true;

        if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.JELLY_BEAN) {
            // Call public methods.
            lineSpacingMultiplier = textView.getLineSpacingMultiplier();
            lineSpacingAdd = textView.getLineSpacingExtra();
            includePad = textView.getIncludeFontPadding();
        } else {
            // Call private methods and make sure to provide fallback defaults in case something
            // goes wrong. The default values have been inlined with the StaticLayout defaults.
            lineSpacingMultiplier = invokeAndReturnWithDefault(textView,
                    "getLineSpacingMultiplier", lineSpacingMultiplier);
            lineSpacingAdd = invokeAndReturnWithDefault(textView,
                    "getLineSpacingExtra", lineSpacingAdd);
            //noinspection ConstantConditions
            includePad = invokeAndReturnWithDefault(textView,
                    "getIncludeFontPadding", includePad);
        }

        // The layout could not be constructed using the builder so fall back to the
        // most broad constructor.
        return new StaticLayout(text, textPaint, availableWidth,
                alignment,
                lineSpacingMultiplier,
                lineSpacingAdd,
                includePad);
    }


    private static <T> T invokeAndReturnWithDefault(@NonNull Object object, @NonNull final String methodName, @NonNull final T defaultValue) {
        T result = null;
        boolean exceptionThrown = false;

        try {
            // Cache lookup.
            Method method = getTextViewMethod(methodName);
            if (method != null) {
                //noinspection unchecked
                result = (T) method.invoke(object);
            }
        } catch (Exception ex) {
            exceptionThrown = true;
            Log.w(TAG, "Failed to invoke TextView#" + methodName + "() method", ex);
        } finally {
            if (result == null && exceptionThrown) {
                result = defaultValue;
            }
        }

        return result;
    }

    @SuppressLint("PrivateApi")
    @Nullable
    private static Method getTextViewMethod(@NonNull final String methodName) {
        try {
            Method method = sTextViewMethodByNameCache.get(methodName);
            if (method == null) {
                method = TextView.class.getDeclaredMethod(methodName);
                if (method != null) {
                    method.setAccessible(true);
                    // Cache update.
                    sTextViewMethodByNameCache.put(methodName, method);
                }
            }
            return method;
        } catch (Exception ex) {
            Log.w(TAG, "Failed to retrieve TextView#" + methodName + "() method", ex);
            return null;
        }
    }
}

三个男躁一个女,国精产品一区一手机的秘密,麦子交换系列最经典十句话,欧美国产综合欧美视频

Android TextView 展開動畫

Android TextView 展開動畫

AutoSizeTextView

三个男躁一个女,国精产品一区一手机的秘密,麦子交换系列最经典十句话,欧美 国产 综合 欧美 视频

Android TextView 展開動畫

AutoSizeTextView

三个男躁一个女,国精产品一区一手机的秘密,麦子交换系列最经典十句话,欧美国产综合欧美视频