Android：简易弹幕效果实现

首先上效果图，类似于360检测到骚扰电话页面：

布局很简单，上面是一个RelativeLayout，下面一个Button.

功能：

（1）弹幕生成后自动从右侧往左侧滚动（TranslateAnimation），弹幕消失后立刻被移除。

（2）弹幕位置随机出现，并且不重复（防止文字重叠）。

（3）字体大小在一定范围内随机改变，字体颜色也可以设置。

（4）自定义先减速，后加速的Interpolator，弹幕加速进入、减速停留、然后加速出去。

1.Activity代码：

/**
 * 简易弹幕效果实现
 * Created by admin on 15-6-4.
 */
public class MainActivity extends ActionBarActivity {
    private MyHandler handler;

    //弹幕内容
    private TanmuBean tanmuBean;
    //放置弹幕内容的父组件
    private RelativeLayout containerVG;

    //父组件的高度
    private int validHeightSpace;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);

        containerVG = (RelativeLayout) findViewById(R.id.tanmu_container);
        tanmuBean = new TanmuBean();
        tanmuBean.setItems(new String[]{"测试一下", "弹幕这东西真不好做啊", "总是出现各种问题~~", "也不知道都是为什么？麻烦！", "哪位大神可以帮帮我啊？", "I need your help.",
                "测试一下", "弹幕这东西真不好做啊", "总是出现各种问题~~", "也不知道都是为什么？麻烦！", "哪位大神可以帮帮我啊？", "I need your help.",
                "测试一下", "弹幕这东西真不好做啊", "总是出现各种问题~~", "也不知道都是为什么？麻烦！", "哪位大神可以帮帮我啊？", "I need your help."});

        handler = new MyHandler(this);

        //开始弹幕
        View startTanmuView = findViewById(R.id.startTanmu);
        startTanmuView.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                if (containerVG.getChildCount() > 0) {
                    return;
                }

                existMarginValues.clear();
                new Thread(new CreateTanmuThread()).start();
            }
        });
    }

    //每2s自动添加一条弹幕
    private class CreateTanmuThread implements Runnable {
        @Override
        public void run() {
            int N = tanmuBean.getItems().length;
            for (int i = 0; i < N; i++) {
                handler.obtainMessage(1, i, 0).sendToTarget();
                SystemClock.sleep(2000);
            }
        }
    }

    //需要在主线城中添加组件
    private static class MyHandler extends Handler {
        private WeakReference<MainActivity> ref;

        MyHandler(MainActivity ac) {
            ref = new WeakReference<>(ac);
        }

        @Override
        public void handleMessage(Message msg) {
            super.handleMessage(msg);

            if (msg.what == 1) {
                MainActivity ac = ref.get();
                if (ac != null && ac.tanmuBean != null) {
                    int index = msg.arg1;
                    String content = ac.tanmuBean.getItems()[index];
                    float textSize = (float) (ac.tanmuBean.getMinTextSize() * (1 + Math.random() * ac.tanmuBean.getRange()));
                    int textColor = ac.tanmuBean.getColor();

                    ac.showTanmu(content, textSize, textColor);
                }
            }
        }
    }

    private void showTanmu(String content, float textSize, int textColor) {
        final TextView textView = new TextView(this);

        textView.setTextSize(textSize);
        textView.setText(content);
//        textView.setSingleLine();
        textView.setTextColor(textColor);

        int leftMargin = containerVG.getRight() - containerVG.getLeft() - containerVG.getPaddingLeft();
        //计算本条弹幕的topMargin(随机值，但是与屏幕中已有的不重复)
        int verticalMargin = getRandomTopMargin();
        textView.setTag(verticalMargin);

        LayoutParams params = new LayoutParams(LayoutParams.WRAP_CONTENT, LayoutParams.WRAP_CONTENT);
        params.addRule(RelativeLayout.ALIGN_PARENT_TOP);
        params.topMargin = verticalMargin;

        textView.setLayoutParams(params);
        Animation anim = AnimationHelper.createTranslateAnim(this, leftMargin, -ScreenUtils.getScreenW(this));
        anim.setAnimationListener(new Animation.AnimationListener() {
            @Override
            public void onAnimationStart(Animation animation) {

            }

            @Override
            public void onAnimationEnd(Animation animation) {
                //移除该组件
                containerVG.removeView(textView);
                //移除占位
                int verticalMargin = (int) textView.getTag();
                existMarginValues.remove(verticalMargin);
            }

            @Override
            public void onAnimationRepeat(Animation animation) {

            }
        });
        textView.startAnimation(anim);

        containerVG.addView(textView);
    }

    //记录当前仍在显示状态的弹幕的位置（避免重复）
    private Set<Integer> existMarginValues = new HashSet<>();
    private int linesCount;

    private int getRandomTopMargin() {
        //计算用于弹幕显示的空间高度
        if (validHeightSpace == 0) {
            validHeightSpace = containerVG.getBottom() - containerVG.getTop()
                    - containerVG.getPaddingTop() - containerVG.getPaddingBottom();
        }

        //计算可用的行数
        if (linesCount == 0) {
            linesCount = validHeightSpace / ScreenUtils.dp2px(this, tanmuBean.getMinTextSize() * (1 + tanmuBean.getRange()));
            if (linesCount == 0) {
                throw new RuntimeException("Not enough space to show text.");
            }
        }

        //检查重叠
        while (true) {
            int randomIndex = (int) (Math.random() * linesCount);
            int marginValue = randomIndex * (validHeightSpace / linesCount);

            if (!existMarginValues.contains(marginValue)) {
                existMarginValues.add(marginValue);
                return marginValue;
            }
        }
    }
}

public class AnimationHelper {
    /**
     * 创建平移动画
     */
    public static Animation createTranslateAnim(Context context, int fromX, int toX) {
        TranslateAnimation tlAnim = new TranslateAnimation(fromX, toX, 0, 0);
        //自动计算时间
        long duration = (long) (Math.abs(toX - fromX) * 1.0f / ScreenUtils.getScreenW(context) * 4000);
        tlAnim.setDuration(duration);
        tlAnim.setInterpolator(new DecelerateAccelerateInterpolator());
        tlAnim.setFillAfter(true);

        return tlAnim;
    }
}

3.自定义的Interpolator，其实只有一行代码

public class DecelerateAccelerateInterpolator implements Interpolator {

    //input从0～1，返回值也从0～1.返回值的曲线表征速度加减趋势
    @Override
    public float getInterpolation(float input) {
        return (float) (Math.tan((input * 2 - 1) / 4 * Math.PI)) / 2.0f + 0.5f;
    }
}

public class TanmuBean {
    private String[] items;
    private int color;
    private int minTextSize;
    private float range;

    public TanmuBean() {
        //init default value
        color = Color.parseColor("#eeeeee");
        minTextSize = 16;
        range = 0.5f;
    }

    public String[] getItems() {
        return items;
    }

    public void setItems(String[] items) {
        this.items = items;
    }

    public int getColor() {
        return color;
    }

    public void setColor(int color) {
        this.color = color;
    }

    /**
     * min textSize, in dp.
     */
    public int getMinTextSize() {
        return minTextSize;
    }

    public void setMinTextSize(int minTextSize) {
        this.minTextSize = minTextSize;
    }

    public float getRange() {
        return range;
    }

    public void setRange(float range) {
        this.range = range;
    }
}