本篇內容介紹了“Android Activity側滑返回的實現原理是什么”的有關知識，在實際案例的操作過程中，不少人都會遇到這樣的困境，接下來就讓小編帶領大家學習一下如何處理這些情況吧！希望大家仔細閱讀，能夠學有所成！
使用側滑Activity返回很常見，例如微信就用到了。那么它是怎么實現的呢。本文帶你剖析一下實現原理。我在github上找了一個star有2.6k的開源，我們分析他是怎么實現的
//star 2.6k 'com.r0adkll:slidableactivity:2.0.5'
它的使用很簡單，首先要設置透明的窗口背景
<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);
步驟一 重新包裹界面
Slidr.class
public static SlidrInterface attach(final Activity activity, final int statusBarColor1, final int statusBarColor2){
//0 創建滑動嵌套界面SliderPanel
final SliderPanel panel = initSliderPanel(activity, null);
//7 Set the panel slide listener for when it becomes closed or opened
// 監聽回調
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 獲取decorview
ViewGroup decorView = (ViewGroup)activity.getWindow().getDecorView();
//4 獲取我們布局的內容并刪除
View oldScreen = decorView.getChildAt(0);
decorView.removeViewAt(0);
//5 Setup the slider panel and attach it to the decor
// 建立滑動嵌套視圖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 把我們的界面布局添加到SliderPanel，并且把SliderPanel添加到decorView中
panel.addView(oldScreen);
decorView.addView(panel, 0);
return panel;
}步驟二 使用ViewDragHelper.class處理滑動手勢
SliderPanel.class
private void init(){
...
//1 ViewDragHelper創建
mDragHelper = ViewDragHelper.create(this, mConfig.getSensitivity(), callback);
mDragHelper.setMinVelocity(minVel);
mDragHelper.setEdgeTrackingEnabled(mEdgePosition);
//2 Setup the dimmer view 添加用于指示滑動過程的View到底層
mDimView = new View(getContext());
mDimView.setBackgroundColor(mConfig.getScrimColor());
mDimView.setAlpha(mConfig.getScrimStartAlpha());
addView(mDimView);
}步驟三 在ViewDragHelper.Callback中處理我們的界面的拖動
我們首先明確ViewDragHelper僅僅是處理ParentView與它子View的關系，不會一直遍歷到最頂層的View。ViewDragHelper的捕獲capture是這樣實現的
@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;
}重點在SliderPanel.class的ViewDragHelper.Callback callback的實現，作者實現實現了很多個方向的滑動處理mLeftCallback、mRightCallback、mTopCallback、mBottomCallback、mVerticalCallback、mHorizontalCallback, 我們取mLeftCallback來分析
private ViewDragHelper.Callback mLeftCallback = new ViewDragHelper.Callback() {
//捕獲View
@Override
public boolean tryCaptureView(View child, int pointerId) {
boolean edgeCase = !mConfig.isEdgeOnly() || mDragHelper.isEdgeTouched(mEdgePosition, pointerId);
//像前面說的，我們的內容是最上層子View，mDecorView這里指的是我們的contentView
return child.getId() == mDecorView.getId() && edgeCase;
}
//拖動， 最終是通過view.offsetLeftAndRight(offset)實現移動
@Override
public int clampViewPositionHorizontal(View child, int left, int dx) {
return clamp(left, 0, mScreenWidth);
}
//滑動范圍
@Override
public int getViewHorizontalDragRange(View child) {
return mScreenWidth;
}
//釋放處理，判斷是滾回屏幕
@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;
}
}
//滾動到left=0(正常布局) 或者 滾動到left=mScreenWidth（滾出屏幕）關閉Activity
mDragHelper.settleCapturedViewAt(settleLeft, releasedChild.getTop());
invalidate();
}
//轉換位置百分比，確定指示層的透明度
@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);
}
//回調到Slidr處理Activity狀態
@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 這里回調到Slidr處理activity.finish()
if(mListener != null) mListener.onClosed();
}
break;
case ViewDragHelper.STATE_DRAGGING:
break;
case ViewDragHelper.STATE_SETTLING:
break;
}
}
};對于mDragHelper.settleCapturedViewAt(settleLeft, releasedChild.getTop());內部是使用Scroller.class輔助滾動，所以要在SliderPanel中重寫View.computeScroll()
@Override
public void computeScroll() {
super.computeScroll();
if(mDragHelper.continueSettling(true)){
ViewCompat.postInvalidateOnAnimation(this);
}
}整體方案如下圖所示
總體來看原理并不復雜, 就是通過ViewDragHelper對View進行拖動。
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