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Activity侧滑返回 剖析Android Activity侧滑返回的实现原理

怪兽N   2021-06-24 我要评论
想了解剖析Android Activity侧滑返回的实现原理的相关内容吗,怪兽N在本文为您仔细讲解Activity侧滑返回的相关知识和一些Code实例,欢迎阅读和指正,我们先划重点:Activity侧滑返回,android,Activity侧滑返回,下面大家一起来学习吧

简介

使用侧滑Activity返回很常见,例如微信就用到了那么它是怎么实现的呢本文带你剖析一下实现原理我在github上找了一个star有2.6k的开源,我们分析他是怎么实现的

//star 2.6k
'com.r0adkll:slidableactivity:2.0.5'

Slidr使用示例

它的使用很简单,首先要设置透明的窗口背景

 <style name="AppTheme"  parent="Theme.AppCompat.Light.DarkActionBar">
        <!-- Customize your theme here. -->
        <item name="android:textAllCaps">false</item>
        <item name="android:windowActionBar">false</item>
        <item name="windowActionBar">false</item>
        <item name="windowNoTitle">true</item>
        <item name="colorPrimary">@color/colorPrimary</item>
        <item name="colorPrimaryDark">@color/colorPrimaryDark</item>
        <item name="colorAccent">@color/colorAccent</item>
        <item name="android:windowIsTranslucent">true</item>
        <item name="android:windowBackground">@android:color/transparent</item>
    </style>

然后

//setContent(View view)后
Slidr.attach(this);

下面可以从三个步骤看其原理

步骤一 重新包裹界面

Slidr.class

 public static SlidrInterface attach(final Activity activity, final int statusBarColor1, final int statusBarColor2){
        //0  创建滑动嵌套界面SliderPanel
		final SliderPanel panel = initSliderPanel(activity, null);

        //7 Set the panel slide listener for when it becomes closed or opened
        // 监听回调
        panel.setOnPanelSlideListener(new SliderPanel.OnPanelSlideListener() {
			...
            //open close等
        });

		// Return the lock interface
		return initInterface(panel);
    }

	private static SliderPanel initSliderPanel(final Activity activity, final SlidrConfig config) {
		//3 获取decorview
		ViewGroup decorView = (ViewGroup)activity.getWindow().getDecorView();
        
        //4 获取我们布局的内容并删除
		View oldScreen = decorView.getChildAt(0);
		decorView.removeViewAt(0);

		//5 Setup the slider panel and attach it to the decor
        // 建立滑动嵌套视图SliderPanel并且添加到DecorView中
		SliderPanel panel = new SliderPanel(activity, oldScreen, config);
		panel.setId(R.id.slidable_panel);
		oldScreen.setId(R.id.slidable_content);
        
        //6 把我们的界面布局添加到SliderPanel,并且把SliderPanel添加到decorView中
		panel.addView(oldScreen);
		decorView.addView(panel, 0);
		return panel;
	}

步骤二 使用ViewDragHelper.class处理滑动手势

SliderPanel.class

private void init(){
    ...
    //1 ViewDragHelper创建
    mDragHelper = ViewDragHelper.create(this, mConfig.getSensitivity(), callback);
    mDragHelper.setMinVelocity(minVel);
    mDragHelper.setEdgeTrackingEnabled(mEdgePosition);

    //2 Setup the dimmer view 添加用于指示滑动过程的View到底层
    mDimView = new View(getContext());
    mDimView.setBackgroundColor(mConfig.getScrimColor());
    mDimView.setAlpha(mConfig.getScrimStartAlpha());
    addView(mDimView);
}

步骤三 在ViewDragHelper.Callback中处理我们的界面的拖动

我们首先明确ViewDragHelper仅仅是处理ParentView与它子View的关系,不会一直遍历到最顶层的ViewViewDragHelper的捕获capture是这样实现的

  @Nullable
    public View findTopChildUnder(int x, int y) {
        final int childCount = mParentView.getChildCount();
        for (int i = childCount - 1; i >= 0; i--) {
            final View child = mParentView.getChildAt(mCallback.getOrderedChildIndex(i));
            if (x >= child.getLeft() && x < child.getRight()
                    && y >= child.getTop() && y < child.getBottom()) {
                return child;
            }
        }
        return null;
    }

重点在SliderPanel.class的ViewDragHelper.Callback callback的实现,作者实现实现了很多个方向的滑动处理mLeftCallback、mRightCallback、mTopCallback、mBottomCallback、mVerticalCallback、mHorizontalCallback, 我们取mLeftCallback来分析

private ViewDragHelper.Callback mLeftCallback = new ViewDragHelper.Callback() {

    //捕获View
    @Override
    public boolean tryCaptureView(View child, int pointerId) {
        boolean edgeCase = !mConfig.isEdgeOnly() || mDragHelper.isEdgeTouched(mEdgePosition, pointerId);
        //像前面说的,我们的内容是最上层子View,mDecorView这里指的是我们的contentView
        return child.getId() == mDecorView.getId() && edgeCase;
    }

    //拖动, 最终是通过view.offsetLeftAndRight(offset)实现移动
    @Override
    public int clampViewPositionHorizontal(View child, int left, int dx) {
        return clamp(left, 0, mScreenWidth);
    }

    //滑动范围
    @Override
    public int getViewHorizontalDragRange(View child) {
        return mScreenWidth;
    }

    //释放处理,判断是滚回屏幕
    @Override
    public void onViewReleased(View releasedChild, float xvel, float yvel) {
        super.onViewReleased(releasedChild, xvel, yvel);

        int left = releasedChild.getLeft();
        int settleLeft = 0;
        int leftThreshold = (int) (getWidth() * mConfig.getDistanceThreshold());
        boolean isVerticalSwiping = Math.abs(yvel) > mConfig.getVelocityThreshold();

        if(xvel > 0){

            if(Math.abs(xvel) > mConfig.getVelocityThreshold() && !isVerticalSwiping){
                settleLeft = mScreenWidth;
            }else if(left > leftThreshold){
                settleLeft = mScreenWidth;
            }

        }else if(xvel == 0){
            if(left > leftThreshold){
                settleLeft = mScreenWidth;
            }
        }
		
        //滚动到left=0(正常布局) 或者 滚动到left=mScreenWidth(滚出屏幕)关闭Activity
        mDragHelper.settleCapturedViewAt(settleLeft, releasedChild.getTop());
        invalidate();
    }

    //转换位置百分比,确定指示层的透明度
    @Override
    public void onViewPositionChanged(View changedView, int left, int top, int dx, int dy) {
        super.onViewPositionChanged(changedView, left, top, dx, dy);
        float percent = 1f - ((float)left / (float)mScreenWidth);

        if(mListener != null) mListener.onSlideChange(percent);

        // Update the dimmer alpha
        applyScrim(percent);
    }

    //回调到Slidr处理Activity状态
    @Override
    public void onViewDragStateChanged(int state) {
        super.onViewDragStateChanged(state);
        if(mListener != null) mListener.onStateChanged(state);
        switch (state){
            case ViewDragHelper.STATE_IDLE:
                if(mDecorView.getLeft() == 0){
                    // State Open
                    if(mListener != null) mListener.onOpened();
                }else{
                    // State Closed  这里回调到Slidr处理activity.finish()
                    if(mListener != null) mListener.onClosed();
                }
                break;
            case ViewDragHelper.STATE_DRAGGING:

                break;
            case ViewDragHelper.STATE_SETTLING:

                break;
        }
    }
};

对于mDragHelper.settleCapturedViewAt(settleLeft, releasedChild.getTop());内部是使用Scroller.class辅助滚动,所以要在SliderPanel中重写View.computeScroll()

@Override
public void computeScroll() {
    super.computeScroll();
    if(mDragHelper.continueSettling(true)){
        ViewCompat.postInvalidateOnAnimation(this);
    }
}

总结

整体方案如下图所示

总体来看原理并不复杂, 就是通过ViewDragHelper对View进行拖动

以上就是Android Activity侧滑返回的实现原理的详细内容,更多关于Activity侧滑返回的资料请关注其它相关文章!


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