Android跑马灯MarqueeView源码解析

跑马灯效果，大家可以去原作者浏览https://github.com/sfsheng0322/MarqueeView
下面看自定义控件的代码

public class MarqueeView extends ViewFlipper {
  private Context mContext;
  private List<String> notices;
  private boolean isSetAnimDuration = false;
  private OnItemClickListener onItemClickListener;
  private int interval = 2000;
  private int animDuration = 500;
  private int textSize = 14;
  private int textColor = 0xffffffff;
  private int gravity = Gravity.LEFT | Gravity.CENTER_VERTICAL;
  private static final int TEXT_GRAVITY_LEFT = 0, TEXT_GRAVITY_CENTER = 1, TEXT_GRAVITY_RIGHT = 2;
  public MarqueeView(Context context, AttributeSet attrs) {
    super(context, attrs);
    init(context, attrs, 0);
  }
  private void init(Context context, AttributeSet attrs, int defStyleAttr) {
    this.mContext = context;
    if (notices == null) {
      notices = new ArrayList<>();
    }
    TypedArray typedArray = getContext().obtainStyledAttributes(attrs, R.styleable.MarqueeViewStyle, defStyleAttr, 0);
    interval = typedArray.getInteger(R.styleable.MarqueeViewStyle_mvInterval, interval);
    isSetAnimDuration = typedArray.hasValue(R.styleable.MarqueeViewStyle_mvAnimDuration);
    animDuration = typedArray.getInteger(R.styleable.MarqueeViewStyle_mvAnimDuration, animDuration);
    if (typedArray.hasValue(R.styleable.MarqueeViewStyle_mvTextSize)) {
      textSize = (int) typedArray.getDimension(R.styleable.MarqueeViewStyle_mvTextSize, textSize);
      textSize = DisplayUtil.px2sp(mContext, textSize);
    }
    textColor = typedArray.getColor(R.styleable.MarqueeViewStyle_mvTextColor, textColor);
    int gravityType = typedArray.getInt(R.styleable.MarqueeViewStyle_mvGravity, TEXT_GRAVITY_LEFT);
    switch (gravityType) {
      case TEXT_GRAVITY_CENTER:
        gravity = Gravity.CENTER;
        break;
      case TEXT_GRAVITY_RIGHT:
        gravity = Gravity.RIGHT | Gravity.CENTER_VERTICAL;
        break;
    }
    typedArray.recycle();
    setFlipInterval(interval);
    Animation animIn = AnimationUtils.loadAnimation(mContext, R.anim.anim_marquee_in);
    if (isSetAnimDuration) animIn.setDuration(animDuration);
    setInAnimation(animIn);
    Animation animOut = AnimationUtils.loadAnimation(mContext, R.anim.anim_marquee_out);
    if (isSetAnimDuration) animOut.setDuration(animDuration);
    setOutAnimation(animOut);
  }
  // 根据公告字符串启动轮播
  public void startWithText(final String notice) {
    if (TextUtils.isEmpty(notice)) return;
    getViewTreeObserver().addOnGlobalLayoutListener(new ViewTreeObserver.OnGlobalLayoutListener() {
      @Override
      public void onGlobalLayout() {
        getViewTreeObserver().removeGlobalOnLayoutListener(this);
        startWithFixedWidth(notice, getWidth());
      }
    });
  }
  // 根据公告字符串列表启动轮播
  public void startWithList(List<String> notices) {
    setNotices(notices);
    start();
  }
  // 根据宽度和公告字符串启动轮播
  private void startWithFixedWidth(String notice, int width) {
    int noticeLength = notice.length();
    int dpW = DisplayUtil.px2dip(mContext, width);
    int limit = dpW / textSize;
    if (dpW == 0) {
      throw new RuntimeException("Please set MarqueeView width !");
    }
    if (noticeLength <= limit) {
      notices.add(notice);
    } else {
      int size = noticeLength / limit + (noticeLength % limit != 0 ? 1 : 0);
      for (int i = 0; i < size; i++) {
        int startIndex = i * limit;
        int endIndex = ((i + 1) * limit >= noticeLength ? noticeLength : (i + 1) * limit);
        notices.add(notice.substring(startIndex, endIndex));
      }
    }
    start();
  }
  // 启动轮播
  public boolean start() {
    if (notices == null || notices.size() == 0) return false;
    removeAllViews();
    for (int i = 0; i < notices.size(); i++) {
      final TextView textView = createTextView(notices.get(i), i);
      final int finalI = i;
      textView.setOnClickListener(new OnClickListener() {
        @Override
        public void onClick(View v) {
          if (onItemClickListener != null) {
            onItemClickListener.onItemClick(finalI, textView);
          }
        }
      });
      addView(textView);
    }
    if (notices.size() > 1) {
      startFlipping();
    }
    return true;
  }
  // 创建ViewFlipper下的TextView
  private TextView createTextView(String text, int position) {
    TextView tv = new TextView(mContext);
    tv.setGravity(gravity);
    tv.setText(text);
    tv.setTextColor(textColor);
    tv.setTextSize(textSize);
    tv.setTag(position);
    return tv;
  }
  public int getPosition() {
    return (int) getCurrentView().getTag();
  }
  public List<String> getNotices() {
    return notices;
  }
  public void setNotices(List<String> notices) {
    this.notices = notices;
  }
  public void setOnItemClickListener(OnItemClickListener onItemClickListener) {
    this.onItemClickListener = onItemClickListener;
  }
  public interface OnItemClickListener {
    void onItemClick(int position, TextView textView);
  }
}

跑马灯view是继承ViewFlipper，可以看到他的结构体

其实ViewFlipper工作机制很简单，如上图，就是将添加到ViewFlipper中的子View按照顺序定时的显示是其中一个子View，其他的子View设置为Gone状态

private Context mContext;
  private List<String> notices;
  private boolean isSetAnimDuration = false;
  private OnItemClickListener onItemClickListener;
  private int interval = 2000;
  private int animDuration = 500;
  private int textSize = 14;
  private int textColor = 0xffffffff;
  private int gravity = Gravity.LEFT | Gravity.CENTER_VERTICAL;
  private static final int TEXT_GRAVITY_LEFT = 0, TEXT_GRAVITY_CENTER = 1, TEXT_GRAVITY_RIGHT = 2;

看出view的一些属性，上下文，集合，是否动画延迟，点击事件，跑马灯的时间间隔，动画延迟时间，字体大小颜色，设置位置在靠左垂直中间对齐，文字的位置常量。

修改MarqueeView的构造方法，我们可以在右键generate快速生成。

<declare-styleable name="MarqueeViewStyle">
    <attr name="mvInterval" format="integer|reference"/>
    <attr name="mvAnimDuration" format="integer|reference"/>
    <attr name="mvTextSize" format="dimension|reference"/>
    <attr name="mvTextColor" format="color|reference"/>
    <attr name="mvGravity">
      <enum name="left" value="0"/>
      <enum name="center" value="1"/>
      <enum name="right" value="2"/>
    </attr>
  </declare-styleable>

TypedArray typedArray = getContext().obtainStyledAttributes(attrs, R.styleable.MarqueeViewStyle, defStyleAttr, 0);

首先获取属性集合，获取一个mv的间隔，默认值2000

 isSetAnimDuration = typedArray.hasValue(R.styleable.MarqueeViewStyle_mvAnimDuration);

是否设置动画时间的延迟

if (typedArray.hasValue(R.styleable.MarqueeViewStyle_mvTextSize)) {
      textSize = (int) typedArray.getDimension(R.styleable.MarqueeViewStyle_mvTextSize, textSize);
      textSize = DisplayUtil.px2sp(mContext, textSize);
    }

假如设置有自定义文字大小，就获取然后px转成sp
获取控件位置，自由设置
在后面要回收

typedArray.recycle();

setFlipInterval(interval);设置滚屏间隔，单位毫秒

Animation animIn = AnimationUtils.loadAnimation(mContext, R.anim.anim_marquee_in);
    if (isSetAnimDuration) animIn.setDuration(animDuration);
    setInAnimation(animIn);
    Animation animOut = AnimationUtils.loadAnimation(mContext, R.anim.anim_marquee_out);
    if (isSetAnimDuration) animOut.setDuration(animDuration);
    setOutAnimation(animOut);

一进一出的动画效果

// 根据公告字符串启动轮播
public void startWithText(final String notice)
暴露个公共方法，里面有测量view的getViewTreeObserver方法，里面内部类调用了startWithFixedWidth(notice, getWidth());方法

 // 根据宽度和公告字符串启动轮播
  private void startWithFixedWidth(String notice, int width) {
    int noticeLength = notice.length();
    int dpW = DisplayUtil.px2dip(mContext, width);
    int limit = dpW / textSize;
    if (dpW == 0) {
      throw new RuntimeException("Please set MarqueeView width !");
    }
    if (noticeLength <= limit) {
      notices.add(notice);
    } else {
      int size = noticeLength / limit + (noticeLength % limit != 0 ? 1 : 0);
      for (int i = 0; i < size; i++) {
        int startIndex = i * limit;
        int endIndex = ((i + 1) * limit >= noticeLength ? noticeLength : (i + 1) * limit);
        notices.add(notice.substring(startIndex, endIndex));
      }
    }
    start();
  }

转换得到一个dp的宽度，限制字数长度大小。假如字符串小于直接add。假如过长取余得到行数。然后循环，获取那行的头尾，末尾假如2行字数还是比总体长度大就取总体长度，假如小于总体长度，就取那行的末尾下表。
然后开始播放

 // 启动轮播
  public boolean start() {
    if (notices == null || notices.size() == 0) return false;
    removeAllViews();
    for (int i = 0; i < notices.size(); i++) {
      final TextView textView = createTextView(notices.get(i), i);
      final int finalI = i;
      textView.setOnClickListener(new OnClickListener() {
        @Override
        public void onClick(View v) {
          if (onItemClickListener != null) {
            onItemClickListener.onItemClick(finalI, textView);
          }
        }
      });
      addView(textView);
    }
    if (notices.size() > 1) {
      startFlipping();
    }
    return true;
  }

创建部署每行的tv

 // 创建ViewFlipper下的TextView
  private TextView createTextView(String text, int position) {
    TextView tv = new TextView(mContext);
    tv.setGravity(gravity);
    tv.setText(text);
    tv.setTextColor(textColor);
    tv.setTextSize(textSize);
    tv.setTag(position);
    return tv;
  }

然后将所有的textview add起来，然后开始播放。后面就是做个点击回调，然后set get这个公告的集合。
最后不要忘了在布局顶层加入

xmlns:app="http://schemas.android.com/apk/res-auto"

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