先來看最終效果圖

LineAnimation.gif

整個(gè)效果圖包括了

Share Element Transition

CollapsingToolbarLayout

AppbarLayout

自定義的動(dòng)畫效果

先來分析自定義動(dòng)畫煤蚌，用兩個(gè)TextView來分別顯示Title(動(dòng)物世界)和SubTitle(春天到了...)。SubTitle的動(dòng)畫需要自己手動(dòng)來畫髓窜，可以直接沿著TextView的周長(zhǎng)來畫線巢株。
我們需要重寫View的onDraw方法赡突，然后在方法體里來畫我們的圖像，然后通過調(diào)用invalidate來刷新View讓畫面動(dòng)起來。
線框的繪畫其實(shí)就是由5條線組合在一起赘被，這里用我用bottom,left,right,topLeft,topRight來代表這5條線悴侵，我們簡(jiǎn)單先給topLeft定義一個(gè)確定的長(zhǎng)度length 等于TextView的寬度1/4瞧剖。
為了讓這些白線有一定的粗細(xì)，我們用canvas.drawRect來畫線而不是用drawLine可免，設(shè)定線的寬度stokeWidth抓于。

所以線框的完全體就是這樣

length = getWidth()/4;
stokeWidth = 2;
@Override
protected void onDraw(Canvas canvas) {
        super.onDraw(canvas);
        //bottom
        canvas.drawRect(0, getHeight() - stokeWidth, getWidth(), getHeight(), paint);
        //left
        canvas.drawRect(0, 0, stokeWidth, getHeight(), paint);
        //right
        canvas.drawRect(getWidth() - stokeWidth, 0, getWidth(), getHeight(), paint);
        //topLeft
        canvas.drawRect(0, 0, length, stokeWidth, paint);
        //topRight
        canvas.drawRect(getWidth() - length, 0, getWidth(), stokeWidth, paint);
}

然后實(shí)現(xiàn)動(dòng)畫：
計(jì)算線框的總長(zhǎng)度（或者說繪制完成時(shí)的長(zhǎng)度） maxRound
動(dòng)畫過程中線框長(zhǎng)度 currentRound
設(shè)置繪制比例值 percent
通過比較currentRound的值畫出對(duì)應(yīng)幀的線框圖像

    @Override
    protected void onDraw(Canvas canvas) {
        super.onDraw(canvas);
        float currentRound = maxRound * percent;
        if (currentRound <= stokeWidth) {
            return;
        }
        //currentRound長(zhǎng)度小于bottom時(shí)，只畫出底部線條
        if (currentRound <= getWidth()) {
            canvas.drawRect((getWidth() - currentRound) / 2, getHeight() - stokeWidth, (getWidth() + currentRound) / 2, getHeight(), paint);
        //blr=bottom+left+right浇借，當(dāng)currentRound小于底邊和左右兩邊加起來的時(shí)候捉撮，畫出對(duì)應(yīng)的線條
        } else if (currentRound <= blr) {
            canvas.drawRect(0, getHeight() - stokeWidth, getWidth(), getHeight(), paint);
            float y = getHeight() - (currentRound - getWidth()) / 2;
            canvas.drawRect(0, y, stokeWidth, getHeight(), paint);
            canvas.drawRect(getWidth() - stokeWidth, y, getWidth(), getHeight(), paint);
        } else {
            //bottom
            canvas.drawRect(0, getHeight() - stokeWidth, getWidth(), getHeight(), paint);
            //left
            canvas.drawRect(0, 0, stokeWidth, getHeight(), paint);
            //right
            canvas.drawRect(getWidth() - stokeWidth, 0, getWidth(), getHeight(), paint);
            //blr為bottom，left妇垢，right加起來的長(zhǎng)度
            float r = (currentRound - blr) / 2;
            //topLeft
            canvas.drawRect(0, 0, r, stokeWidth, paint);
            //topRight
            canvas.drawRect(getWidth() - r, 0, getWidth(), stokeWidth, paint);
        }
    }
    //通過屬性動(dòng)畫來畫出幀動(dòng)畫
    public void animate(float f) {
        ValueAnimator valueAnimator = new ValueAnimator();
        valueAnimator.setFloatValues(percent, f);
        valueAnimator.setDuration(500);
        valueAnimator.addUpdateListener(this);
        valueAnimator.start();
    }
    //監(jiān)聽屬性動(dòng)畫回調(diào)改變繪畫的線框百分比percent
    @Override
    public void onAnimationUpdate(ValueAnimator animation) {
        percent= (float) animation.getAnimatedValue();
        setTextColor(Color.argb((int) (percent * 255), 255, 255, 255));
        invalidate();
    }

順手給subTitle文字加個(gè)漸變巾遭，效果大概就是這樣

pic2.gif

接下來是讓動(dòng)畫和AppbarLayout的滑動(dòng)事件關(guān)聯(lián)起來
xml布局

<?xml version="1.0" encoding="utf-8"?>
<android.support.design.widget.CoordinatorLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:app="http://schemas.android.com/apk/res-auto"
    xmlns:tools="http://schemas.android.com/tools"
    android:layout_width="match_parent"
    android:layout_height="match_parent">

    <android.support.design.widget.AppBarLayout
        android:id="@+id/app_bar"
        android:layout_width="match_parent"
        android:layout_height="150dp"
        app:elevation="0dp">

        <android.support.design.widget.CollapsingToolbarLayout
            android:id="@+id/collapsingToolbar"
            android:layout_width="match_parent"
            android:layout_height="match_parent"
            app:expandedTitleMarginEnd="64dp"
            app:expandedTitleMarginStart="48dp"
            app:layout_scrollFlags="scroll|exitUntilCollapsed|snap">

            <com.facebook.drawee.view.SimpleDraweeView
                android:id="@+id/bgImageView"
                android:layout_width="match_parent"
                android:layout_height="match_parent"
                app:layout_collapseMode="parallax"
                app:layout_collapseParallaxMultiplier="0.5"
                tools:background="#cccccc" />

            <View
                android:layout_width="match_parent"
                android:layout_height="match_parent"
                android:background="#55000000" />

            <android.support.v7.widget.Toolbar
                android:id="@+id/toolbar"
                android:layout_width="match_parent"
                android:layout_height="?attr/actionBarSize"
                app:contentInsetLeft="0dp"
                app:contentInsetStart="0dp"
                app:layout_collapseMode="pin" />

            <TextView
                android:id="@+id/title"
                android:layout_width="wrap_content"
                android:layout_height="wrap_content"
                android:layout_gravity="center_horizontal"
                android:layout_marginTop="48dp"
                android:maxLines="1"
                android:paddingLeft="8dp"
                android:paddingRight="8dp"
                android:textColor="@color/white"
                android:textSize="18dp"
                android:textStyle="bold"
                app:layout_collapseMode="parallax"
                tools:text="走進(jìn)科學(xué)" />

        </android.support.design.widget.CollapsingToolbarLayout>

    </android.support.design.widget.AppBarLayout>

    <android.support.v7.widget.RecyclerView
        android:id="@+id/recyclerView"
        android:layout_width="match_parent"
        android:layout_height="match_parent"
        app:layout_behavior="@string/appbar_scrolling_view_behavior" />

    <etong.lineanimation.SubTitleView
        android:id="@+id/subTitle"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_gravity="center_horizontal"
        android:layout_marginTop="58dp"
        android:gravity="center"
        android:maxLines="2"
        android:paddingBottom="12dp"
        android:paddingLeft="20dp"
        android:paddingRight="20dp"
        android:paddingTop="20dp"
        android:textColor="@color/white"
        android:textSize="14dp"
        tools:text="春天到了肉康，又到了交配的季節(jié)。" />


    <Button
        android:id="@+id/button"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text="show"
        android:layout_gravity="bottom"/>
</android.support.design.widget.CoordinatorLayout>

設(shè)置AppBarLayout監(jiān)聽
appBar.addOnOffsetChangedListener(this);
根據(jù)滑動(dòng)距離來和最大滑動(dòng)距離來計(jì)算線框繪制的百分比

    @Override
    public void onOffsetChanged(AppBarLayout appBarLayout, int verticalOffset) {
        if (!TextUtils.isEmpty(subTitle)) {
            float value = appBar.getHeight() - toolbar.getHeight() * 2;
            float p = (value + verticalOffset) / value;
            if (p < 0) {
                p = 0;
            }
            subTitleView.setPercent(p);
        }
   }

這里線框的位置是固定的灼舍，所以在appBarLayout滑動(dòng)的時(shí)候?yàn)榱吮苊饩€框出界吼和，需要線框提前一點(diǎn)消失，所以本來最大滑動(dòng)距離為
appBar.getHeight()-toolbar.getHeight()
改為
appBar.getHeight() - toolbar.getHeight() * 2
效果

pic3.gif

接下來需要處理一下SubTtileView本身高寬和主標(biāo)題Title所在TextView的寬度問題骑素。

• Title最大行數(shù)為一行炫乓，SubTitle最大行數(shù)為兩行
• SubTtileView本身的最大寬度也必須小于屏幕寬度，而且需要有最小的左右邊距 padding
• SubTitleView的topLeft和topRight必須留有一點(diǎn)的長(zhǎng)度献丑，才能形成一個(gè)完整的線框 minLength
• Title文字過多的時(shí)候會(huì)占滿屏幕末捣，所以必須限制Title的最大寬度
  maxTitleWidth = screenWidth - padding * 2 - minLength * 2
• SubTitleView的寬度必須大于Title的寬度，所以我們要根據(jù)Title的寬度手動(dòng)計(jì)算SubTitleView的寬度
  minSubTitleViewWidth = titleWidth - minLenght * 2
• ............

subtitleMargin = getResources().getDimensionPixelSize(R.dimen.subtitle_margin);
minLength = getResources().getDimensionPixelSize(R.dimen.min_length);
maxTitleWidth = ScreenUtils.screenWidth - subtitleMargin * 2 - minLength * 2;

    public void calculateSubTitle() {
        int titleWidth = titleTextView.getWidth();

        if (titleWidth > maxTitleWidth) {
            titleTextView.getLayoutParams().width = maxTitleWidth;
            subtitleView.getLayoutParams().width = maxTitleWidth + minLength * 2;
            subtitleView.setLength(minLength * 2);
            subtitleView.requestLayout();
            titleTextView.requestLayout();
        } else if (subtitleView.getWidth() > ScreenUtils.screenWidth - subtitleMargin * 2) {
            subtitleView.getLayoutParams().width = ScreenUtils.screenWidth - subtitleMargin * 2;
            subtitleView.setLength(subtitleView.getLayoutParams().width - titleWidth);
            subtitleView.requestLayout();
        } else if (subtitleView.getWidth() < titleWidth + minLength * 2) {
            subtitleView.getLayoutParams().width = titleWidth + minLength * 2;
            subtitleView.setLength(subtitleView.getLayoutParams().width - titleWidth);
            subtitleView.requestLayout();
        } else {
            subtitleView.setLength(subtitleView.getLayoutParams().width - titleWidth);
            subtitleView.requestLayout();
        }
    }

到此所有的自定義部分就寫完了创橄，剩下的過場(chǎng)動(dòng)畫由于是Android支持庫(kù)的api就不多解釋箩做。
最后，源碼鏈接 https://github.com/RoyWallace/LineAnimation
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