SlidingDrawer源码分析

一属性变量分析

构造函数完成获取attr属性内容的读取，读取用户配置的UI属性，用于构造新的UI结构。

属性内容为，注意这里的SlidingShow作者自己定义的，拷自源码包：

<resources>
    <declare-styleable name="SlidingShow">
        <attr name="handle" format="reference" />
        <attr name="content" format="reference" />
        <attr name="orientation"  format="integer" />
        <attr name="bottomOffset" format="dimension" />
        <attr name="topOffset" format="dimension" />
        <attr name="allowSingleTap" format="boolean" />
        <attr name="animateOnClick" format="boolean" />
    </declare-styleable>
</resources>

android:allowSingleTap：指示是否可以通过handle打开或关闭

android:animateOnClick：指示是否当使用者按下手柄打开/关闭时是否该有一个动画。

android:content：隐藏的内容

android:handle：handle（手柄）

二源码情景分析

在分析源码前，先要选择一个分析顺序，顺序按照ViewGroup绘制周期来进展。

根据viewGroup的绘制顺序开始分析源码。

2.1 测量函数

    @Override
    protected void onMeasure(int widthMeasureSpec, int heightMeasureSpec) {(1)
        int widthSpecMode = MeasureSpec.getMode(widthMeasureSpec);
        int widthSpecSize = MeasureSpec.getSize(widthMeasureSpec);

        int heightSpecMode = MeasureSpec.getMode(heightMeasureSpec);
        int heightSpecSize = MeasureSpec.getSize(heightMeasureSpec);
        final View handle = mHandle;
        measureChild(handle, widthMeasureSpec, heightMeasureSpec);//（2）获取child View的大小
        //定义mContent大小
        if (mVertical) {
            int height = heightSpecSize - handle.getMeasuredHeight() - mTopOffset;(3)
            mContent.measure(MeasureSpec.makeMeasureSpec(widthSpecSize, MeasureSpec.EXACTLY),
                    MeasureSpec.makeMeasureSpec(height, MeasureSpec.EXACTLY));
        } else {
            int width = widthSpecSize - handle.getMeasuredWidth() - mTopOffset;
            mContent.measure(MeasureSpec.makeMeasureSpec(width, MeasureSpec.EXACTLY),
                    MeasureSpec.makeMeasureSpec(heightSpecSize, MeasureSpec.EXACTLY));
        }
        setMeasuredDimension(widthSpecSize, heightSpecSize);
    }

(1) widthMeasureSpec和heightMeasureSpec为宽度规格和高度规格，可以获取对应的mode(AT_MOST尽大/  EXACTLY精确/  UNSPECIFIED不限制)，可以获取对应尺寸。

(2) 获取viewGroup中子视图的尺寸，这里是获取handle的View大小。

(3) 根据对应的偏移量和handle view的大小，设置Content大小。

2.2 视图函数

    @Override
    protected void onLayout(boolean changed, int l, int t, int r, int b) {(1)
        if (mTracking) {
            return;
        }
        final int width = r - l;    //viewGroup的宽度
        final int height = b - t;   //viewGroup的高度
        final View handle = mHandle;

        int childWidth = handle.getMeasuredWidth();     //handle尺寸
        int childHeight = handle.getMeasuredHeight();
        int childLeft;
        int childTop;
        final View content = mContent;
        if (mVertical) {
            childLeft = (width - childWidth) / 2;
            /**
             * 设定hanlde位置，这里handle与mBottomOffset和自己大小有关
             * 设定content位置，这里content与mTopOffset和handle大小有关
             */
            childTop = mExpanded ? mTopOffset : height - childHeight + mBottomOffset;(2)
            //设定content的位置
            content.layout(0, mTopOffset + childHeight, content.getMeasuredWidth(),
                    mTopOffset + childHeight + content.getMeasuredHeight());
        } else {
            childLeft = mExpanded ? mTopOffset : width - childWidth + mBottomOffset;
            childTop = (height - childHeight) / 2;

            content.layout(mTopOffset + childWidth, 0,
                    mTopOffset + childWidth + content.getMeasuredWidth(),
                    content.getMeasuredHeight());
        }
        //确定handle位置
        handle.layout(childLeft, childTop, childLeft + childWidth, childTop + childHeight);(3)
        mHandleHeight = handle.getHeight();
        mHandleWidth = handle.getWidth();
    }

(1) 参数changed表示view有新的尺寸或位置；参数l表示相对于父view的Left位置；参数t表示相对于父view的Top位置；参数r表示相对于父view的Right位置；参数b表示相对于父view的Bottom位置。

(2) 问号表达式，根据条件展开或是收缩决定handle的Top位置。

(3) 确定handle位置，包含了展开和收缩的判定，这里Content位置还不太对，还显示在expanded（展开状态）。

2.3 绘制图像函数

    @Override
    protected void dispatchDraw(Canvas canvas) {    //绘制两个子view
        final long drawingTime = getDrawingTime();  //获取当前GPU绘制view时间，不是日期时间(1)
        final View handle = mHandle;
        final boolean isVertical = mVertical;

        drawChild(canvas, handle, drawingTime);(1)
        if (mTracking || mAnimating) {      //判断当前状态是否为追踪或者发生动画状态
            final Bitmap cache = mContent.getDrawingCache();
            if (cache != null) {
                if (isVertical) {
                    canvas.drawBitmap(cache, 0, handle.getBottom(), null);
                } else {
                    canvas.drawBitmap(cache, handle.getRight(), 0, null);
                }
            } else {
                canvas.save();
                canvas.translate(isVertical ? 0 : handle.getLeft() - mTopOffset,
                        isVertical ? handle.getTop() - mTopOffset : 0);(2)
                drawChild(canvas, mContent, drawingTime);
                canvas.restore();   //更改save方法前所有的绘制修改
            }
        } else if (mExpanded) {
            drawChild(canvas, mContent, drawingTime);(3)
        }
    }

(1)根据当前配置的canvas绘制handle

(2)更改相应的canvas配置，用户绘制content

(3)根据当前配置的canvas绘制content

2.4 完成绘制函数

    @Override
    protected void onFinishInflate() {
        mHandle = findViewById(mHandleId);
        if (mHandle == null) {
            throw new IllegalArgumentException("The handle attribute is must refer to an"
                    + " existing child.");
        }
        mHandle.setOnClickListener(new DrawerToggler());//设置单击监听类（1）
        mContent = findViewById(mContentId);
        if (mContent == null) {
            throw new IllegalArgumentException("The content attribute is must refer to an"
                    + " existing child.");
        }
        mContent.setVisibility(View.GONE);
    }

(1)设置监听类，内部设置相应的点击事件动画。

2.4.1 监听类的解析

    private class DrawerToggler implements OnClickListener {
        public void onClick(View v) {
            if (mLocked) {(1)
                return;
            }
            // mAllowSingleTap isn't relevant here; you're *always*
            // allowed to open/close the drawer by clicking with the
            // trackball.
            //android:allowSingleTap：指示是否可以通过handle打开或关闭
            //android:animateOnClick：指示是否当使用者按下手柄打开/关闭时是否该有一个动画。
            if (mAnimateOnClick) {(2)
                animateToggle();(3)
            } else {
                toggle();(4)
            }
        }
    }

(1)判断是否将view锁住，不允许点击。

(2)判断是否使用单击动画，可以不使用，可以使用。
(3)animateToggle()方法，单击后的动画效果

    public void animateToggle() {
        if (!mExpanded) {
            animateOpen();
        } else {
            animateClose();
        }
    }

展开和收缩两种动画效果：

    public void animateOpen() {
        prepareContent();   //准备content(-1)
        final OnDrawerScrollListener scrollListener = mOnDrawerScrollListener;
        if (scrollListener != null) {
            scrollListener.onScrollStarted();//调用onScrollStarted函数
        }
        animateOpen(mVertical ? mHandle.getTop() : mHandle.getLeft());//展开动画(-2)
        sendAccessibilityEvent(AccessibilityEvent.TYPE_WINDOW_STATE_CHANGED);//设定当前的accessibilityEvent
        
        if (scrollListener != null) {
            scrollListener.onScrollEnded(); //调用onScrollEnded函数
        }
    }

(-1)准备content

    private void prepareContent() {
        if (mAnimating) {
            return;
        }

        // Something changed in the content, we need to honor the layout request
        // before creating the cached bitmap
        final View content = mContent;
        if (content.isLayoutRequested()) {
            if (mVertical) {
                final int childHeight = mHandleHeight;
                int height = getBottom() - getTop() - childHeight - mTopOffset;
                content.measure(MeasureSpec.makeMeasureSpec(getRight() - getLeft(), MeasureSpec.EXACTLY),
                        MeasureSpec.makeMeasureSpec(height, MeasureSpec.EXACTLY));
                content.layout(0, mTopOffset + childHeight, content.getMeasuredWidth(),
                        mTopOffset + childHeight + content.getMeasuredHeight());
            } else {
                final int childWidth = mHandle.getWidth();
                int width = getRight() - getLeft() - childWidth - mTopOffset;
                content.measure(MeasureSpec.makeMeasureSpec(width, MeasureSpec.EXACTLY),
                        MeasureSpec.makeMeasureSpec(getBottom() - getTop(), MeasureSpec.EXACTLY));
                content.layout(childWidth + mTopOffset, 0,
                        mTopOffset + childWidth + content.getMeasuredWidth(),
                        content.getMeasuredHeight());
            }
        }
        // Try only once... we should really loop but it's not a big deal
        // if the draw was cancelled, it will only be temporary anyway
        content.getViewTreeObserver().dispatchOnPreDraw();
        if (!content.isHardwareAccelerated()) content.buildDrawingCache();

        content.setVisibility(View.GONE);
//        mContent.setVisibility(View.VISIBLE);
    }

重新绘制content，设计相应的measure() layout()等方法。 跟onLayout(boolean changed, int l, int t, int r, int b)方法中绘制content相同。

(-2)动画展开aimateOpen(boolean)方法

    private void animateOpen(int position) {
        prepareTracking(position);//准备路径
        performFling(position, -mMaximumAcceleration, true);//执行跳动
    }

    private void prepareTracking(int position) {
        mTracking = true;//设置标志位
        mVelocityTracker = VelocityTracker.obtain();(--1)
        boolean opening = !mExpanded;
        if (opening) {
            mAnimatedAcceleration = mMaximumAcceleration;   //加速度设定
            mAnimatedVelocity = mMaximumMajorVelocity;      //最大速度设定
            mAnimationPosition = mBottomOffset +
                    (mVertical ? getHeight() - mHandleHeight : getWidth() - mHandleWidth);
            moveHandle((int) mAnimationPosition);   //移动动画(--2)
            mAnimating = true;
            mHandler.removeMessages(MSG_ANIMATE);(--3)
            long now = SystemClock.uptimeMillis();
            mAnimationLastTime = now;   //记录时间
            mCurrentAnimationTime = now + ANIMATION_FRAME_DURATION;
            mAnimating = true;
        } else {
            if (mAnimating) {
                mAnimating = false;
                mHandler.removeMessages(MSG_ANIMATE);
            }
            moveHandle(position);(--4)
        }
    }

(--1) 速度追踪器获取

(--2) 处理移动操作，moveHandle

    private void moveHandle(int position) {
        final View handle = mHandle;

        if (mVertical) {
            if (position == EXPANDED_FULL_OPEN) {//完全展开
                handle.offsetTopAndBottom(mTopOffset - handle.getTop());//设定水平偏移量
                invalidate();
            } else if (position == COLLAPSED_FULL_CLOSED) {//完全关闭
                handle.offsetTopAndBottom(mBottomOffset + getBottom() - getTop() -
                        mHandleHeight - handle.getTop());
                invalidate();
            } else {
                final int top = handle.getTop();//中间状态
                int deltaY = position - top;
                if (position < mTopOffset) {
                    deltaY = mTopOffset - top;
                } else if (deltaY > mBottomOffset + getBottom() - getTop() - mHandleHeight - top) {
                    deltaY = mBottomOffset + getBottom() - getTop() - mHandleHeight - top;
                }
                handle.offsetTopAndBottom(deltaY);

                final Rect frame = mFrame;
                final Rect region = mInvalidate;

                handle.getHitRect(frame);
                region.set(frame);

                region.union(frame.left, frame.top - deltaY, frame.right, frame.bottom - deltaY);
                region.union(0, frame.bottom - deltaY, getWidth(),
                        frame.bottom - deltaY + mContent.getHeight());

                invalidate(region);
            }
        } else {
            ......
        }
    }

(--3) 移除动画消息
(--4) 移动到相应位置

2.4.1总结animateClose();和animateOpen();基本上一样这里就不在描述了。toggle();更是简单了很多，没有对应的动画，这里也不再分析。

2.5 滑动事件处理

        前面的介绍中，首先描绘如何绘制一个View，并给出了绘制顺序；后来设计了相应的点击事件处理，并提供了有动画和无动画两种情况下的处理函数；那么最后则是处理滑动或者多点触控的事件。

这里会用到两个方法，都是viewGroup的方法，分别是onInterceptTouchEvent()和onTouchEvent()方法，执行顺序遵循下面五点：

1. down事件首先会传递到onInterceptTouchEvent()方法
2. 如果该ViewGroup的onInterceptTouchEvent()在接收到down事件处理完成之后return false，那么后续的move, up等事件将继续会先传递给该ViewGroup，之后才和down事件一样传递给最终的目标view的onTouchEvent()处理。
3. 如果该ViewGroup的onInterceptTouchEvent()在接收到down事件处理完成之后return true，那么后续的move, up等事件将不再传递给onInterceptTouchEvent()，而是和down事件一样传递给该ViewGroup的onTouchEvent()处理，注意，目标view将接收不到任何事件。
4. 如果最终需要处理事件的view的onTouchEvent()返回了false，那么该事件将被传递至其上一层次的view的onTouchEvent()处理。
5. 如果最终需要处理事件的view 的onTouchEvent()返回了true，那么后续事件将可以继续传递给该view的onTouchEvent()处理。

    @Override
    public boolean onInterceptTouchEvent(MotionEvent event) {
        if (mLocked) {
            return false;
        }
        final int action = event.getAction();
        float x = event.getX();
        float y = event.getY();

        final Rect frame = mFrame;
        final View handle = mHandle;

        handle.getHitRect(frame);//找到控件占据的矩形区域的矩形坐标
        if (!mTracking && !frame.contains((int) x, (int) y)) {
            return false;
        }

        if (action == MotionEvent.ACTION_DOWN) {
            mTracking = true;//规划路径中

            handle.setPressed(true);
            // Must be called before prepareTracking()
            prepareContent();

            // Must be called after prepareContent()
            if (mOnDrawerScrollListener != null) {
                mOnDrawerScrollListener.onScrollStarted();
            }

            if (mVertical) {
                final int top = mHandle.getTop();
                mTouchDelta = (int) y - top;
                prepareTracking(top);//设定当前位置
            } else {
                final int left = mHandle.getLeft();
                mTouchDelta = (int) x - left;
                prepareTracking(left);
            }
            mVelocityTracker.addMovement(event);
        }

        return true;//返回true，Event交由onTouchEvent处理
    }

    @Override
    public boolean onTouchEvent(MotionEvent event) {
        if (mLocked) {
            return true;
        }

        if (mTracking) {
            mVelocityTracker.addMovement(event);
            final int action = event.getAction();
            switch (action) {
                case MotionEvent.ACTION_MOVE://移动操作
                    moveHandle((int) (mVertical ? event.getY() : event.getX()) - mTouchDelta);
                    break;
                case MotionEvent.ACTION_UP:
                case MotionEvent.ACTION_CANCEL: {
                    final VelocityTracker velocityTracker = mVelocityTracker;
                    velocityTracker.computeCurrentVelocity(mVelocityUnits);

                    float yVelocity = velocityTracker.getYVelocity();
                    float xVelocity = velocityTracker.getXVelocity();//计算路径的点
                    boolean negative;

                    final boolean vertical = mVertical;
                    if (vertical) {
                        negative = yVelocity < 0;
                        if (xVelocity < 0) {
                            xVelocity = -xVelocity;
                        }
                        if (xVelocity > mMaximumMinorVelocity) {
                            xVelocity = mMaximumMinorVelocity;
                        }
                    } else {
                        negative = xVelocity < 0;
                        if (yVelocity < 0) {
                            yVelocity = -yVelocity;
                        }
                        if (yVelocity > mMaximumMinorVelocity) {
                            yVelocity = mMaximumMinorVelocity;
                        }
                    }

                    float velocity = (float) Math.hypot(xVelocity, yVelocity);// sqrt(x2+ y2).
                    if (negative) {
                        velocity = -velocity;
                    }

                    final int top = mHandle.getTop();
                    final int left = mHandle.getLeft();

                    if (Math.abs(velocity) < mMaximumTapVelocity) {
                        if (vertical ? (mExpanded && top < mTapThreshold + mTopOffset) ||
                                (!mExpanded && top > mBottomOffset + getBottom() - getTop() -
                                        mHandleHeight - mTapThreshold) :
                                (mExpanded && left < mTapThreshold + mTopOffset) ||
                                        (!mExpanded && left > mBottomOffset + getRight() - getLeft() -
                                                mHandleWidth - mTapThreshold)) {

                            if (mAllowSingleTap) {//是否通过点击打开
                                playSoundEffect(SoundEffectConstants.CLICK);

                                if (mExpanded) {
                                    animateClose(vertical ? top : left);
                                } else {
                                    animateOpen(vertical ? top : left);
                                }
                            } else {
                                performFling(vertical ? top : left, velocity, false);//执行松开手的后面运动(1)
                            }

                        } else {
                            performFling(vertical ? top : left, velocity, false);
                        }
                    } else {
                        performFling(vertical ? top : left, velocity, false);
                    }
                }
                break;
            }
        }

        return mTracking || mAnimating || super.onTouchEvent(event);
    }

(1)松开手后的处理函数

private void performFling(int position, float velocity, boolean always) {
        mAnimationPosition = position;
        mAnimatedVelocity = velocity;   //手势控制速度

        if (mExpanded) {
            if (always || (velocity > mMaximumMajorVelocity ||
                    (position > mTopOffset + (mVertical ? mHandleHeight : mHandleWidth) &&
                            velocity > -mMaximumMajorVelocity))) {
                // We are expanded, but they didn't move sufficiently to cause
                // us to retract.  Animate back to the expanded position.
                mAnimatedAcceleration = mMaximumAcceleration;
                if (velocity < 0) {
                    mAnimatedVelocity = 0;
                }
            } else {
                // We are expanded and are now going to animate away.
                mAnimatedAcceleration = -mMaximumAcceleration;
                if (velocity > 0) {
                    mAnimatedVelocity = 0;
                }
            }
        } else {
            if (!always && (velocity > mMaximumMajorVelocity ||
                    (position > (mVertical ? getHeight() : getWidth()) / 2 &&
                            velocity > -mMaximumMajorVelocity))) {
                // We are collapsed, and they moved enough to allow us to expand.
                mAnimatedAcceleration = mMaximumAcceleration;
                if (velocity < 0) {
                    mAnimatedVelocity = 0;
                }
            } else {
                // We are collapsed, but they didn't move sufficiently to cause
                // us to retract.  Animate back to the collapsed position.
                mAnimatedAcceleration = -mMaximumAcceleration;
                if (velocity > 0) {
                    mAnimatedVelocity = 0;
                }
            }
        }

        long now = SystemClock.uptimeMillis();
        mAnimationLastTime = now;
        mCurrentAnimationTime = now + ANIMATION_FRAME_DURATION;
        mAnimating = true;
        mHandler.removeMessages(MSG_ANIMATE);
        mHandler.sendMessageAtTime(mHandler.obtainMessage(MSG_ANIMATE), mCurrentAnimationTime);
        stopTracking();//结束动画
    }

计算接下来运动所需要的参量，发送handler执行后面的动画。

   private void doAnimation() {
        if (mAnimating) {
            incrementAnimation();
            if (mAnimationPosition >= mBottomOffset + (mVertical ? getHeight() : getWidth()) - 1) {
                mAnimating = false;
                closeDrawer();
            } else if (mAnimationPosition < mTopOffset) {
                mAnimating = false;
                openDrawer();
            } else {
                moveHandle((int) mAnimationPosition);
                mCurrentAnimationTime += ANIMATION_FRAME_DURATION;
                mHandler.sendMessageAtTime(mHandler.obtainMessage(MSG_ANIMATE),
                        mCurrentAnimationTime);//循环消息
            }
        }
    }

    private void incrementAnimation() {
        long now = SystemClock.uptimeMillis();
        float t = (now - mAnimationLastTime) / 1000.0f;                   // ms -> s
        final float position = mAnimationPosition;
        final float v = mAnimatedVelocity;                                // px/s
        final float a = mAnimatedAcceleration;                            // px/s/s
        mAnimationPosition = position + (v * t) + (0.5f * a * t * t);     // px
        mAnimatedVelocity = v + (a * t);                                  // px/s
        mAnimationLastTime = now;                                         // ms
    }

    private class SlidingHandler extends Handler {
        public void handleMessage(Message m) {
            switch (m.what) {
                case MSG_ANIMATE:
                    doAnimation();
                    break;
            }
        }
    }