效果：

核心思想：

• 自定義ViewGroup控制元件，利用ViewDragHelper讓此控制元件擁有滑動功能。
• 將此控制元件附加到每一個Activity。

程式碼很簡單就不一一解釋了，程式碼備註很詳細，所以直接貼程式碼了：

import android.app.Activity;
import android.content.Context;
import android.support.annotation.NonNull;
import android.support.v4.widget.ViewDragHelper;
import android.view.MotionEvent;
import
 
 android.view.View;
import android.view.ViewGroup;
import android.widget.FrameLayout;

import view.peakchao.view.R;

/**
 * 基於ViewDragHelper的側滑關閉View
 * Created by Chao on 2018-09-09.
 */

public class SwipeBackLayout extends FrameLayout {
    private ViewDragHelper mHelper;
    private Activity mActivity;
    private
 
 View mView;

    public SwipeBackLayout(@NonNull Context context) {
        super(context);
        initViewDragHelper();
    }


    /**
     * 繫結 Activity
     *
     * @param activity 容器 Activity
     */
    public void attachActivity(Activity activity) {
        mActivity = activity;
        ViewGroup decor = (ViewGroup) activity.getWindow().getDecorView();
        View content = decor.getChildAt(0
 
);
        decor.removeView(content);
        mView = content;
        addView(content);
        decor.addView(this);
    }

    /**
     * 初始化方法
     */
    private void initViewDragHelper() {
        mHelper = ViewDragHelper.create(this, 1.0f, new ViewDragHelper.Callback() {
            @Override
            public boolean tryCaptureView(View child, int pointerId) {
                // 預設不撲獲 View
                return false;
            }

            @Override
            public int clampViewPositionHorizontal(View child, int left, int dx) {
                // 拖動限制（大於左邊界）
                return Math.max(0, left);
            }

            @Override
            public int clampViewPositionVertical(View child, int top, int dy) {
                //左右側滑時，限制不能上下拖動。
                return 0;
            }

            @Override
            public void onViewReleased(View releasedChild, float xvel, float yvel) {
                // 拖動距離大於螢幕的一半右移，拖動距離小於螢幕的一半左移
                int left = releasedChild.getLeft();
                if (left > getWidth() / 2) {
                    if (mActivity != null) {
                        mActivity.finish();
                        mActivity.overridePendingTransition(0, R.anim.right_out);
                    }
                } else {
                    mHelper.settleCapturedViewAt(0, 0);
                }
                invalidate();
            }

            @Override
            public void onEdgeDragStarted(int edgeFlags, int pointerId) {
                // 移動子 View
                mHelper.captureChildView(mView, pointerId);
            }
        });
        // 跟蹤左邊界拖動
        mHelper.setEdgeTrackingEnabled(ViewDragHelper.EDGE_LEFT);
    }


    @Override
    public boolean onInterceptTouchEvent(MotionEvent ev) {
        // 攔截代理
        return mHelper.shouldInterceptTouchEvent(ev);
    }

    @Override
    public boolean onTouchEvent(MotionEvent event) {
        // Touch Event 代理
        mHelper.processTouchEvent(event);
        return true;
    }

    @Override
    public void computeScroll() {
        // 子 View 需要更新狀態
        if (mHelper.continueSettling(true)) {
            invalidate();
        }
    }

}

編寫公共父類，或者將此類下面程式碼新增到需要側滑關閉的Activity即可：

import android.content.Intent;
import android.os.Bundle;
import android.support.annotation.Nullable;
import android.support.v7.app.AppCompatActivity;
import android.view.View;

import view.peakchao.view.R;
import view.peakchao.view.view.SwipeBackLayout;

/**
 * Created by Chao on 2018-09-09.
 */

public class SwipeActivity extends AppCompatActivity {
    private SwipeBackLayout mSwipeBackLayout;

    @Override
    protected void onCreate(@Nullable Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_swipe);//如果此類作為基類，這裡layout需要從子類獲取
        mSwipeBackLayout = new SwipeBackLayout(this);
    }

    @Override
    protected void onPostCreate(@Nullable Bundle savedInstanceState) {
        super.onPostCreate(savedInstanceState);
        mSwipeBackLayout.attachActivity(this);
    }

    public void start(View view) {
        startActivity(new Intent(this, SwipeActivity.class));
    }
}

麻雀雖小五臟俱全，雖看似簡單，但是功能都已經達到了，在此基礎上稍稍改動即可做成微信那種視差特效的側滑關閉了，本來打算做成那樣的，可是這會兒有事，要出門了，見諒。