需求是需要在一个已经存在的页面添加一个可拖动的浮层广告。
使用到的技术：ViewDragHelper

效果如图：

Paste_Image.png

封装好的类（继承自FrameLayout）

import android.content.Context;
import android.support.annotation.AttrRes;
import android.support.annotation.NonNull;
import android.support.annotation.Nullable;
import android.support.v4.widget.ViewDragHelper;
import android.util.AttributeSet;
import android.view.MotionEvent;
import android.view.View;
import android.widget.FrameLayout;

import java.util.ArrayList;

/**
 * Created by hq on 2017/10/10.
 */
public class DragFrameLayout extends FrameLayout {

    String TAG = "DragFrameLayout";
    ViewDragHelper dragHelper;
    ArrayList<View> viewList;
    public DragFrameLayout(@NonNull Context context) {
        this(context, null);
    }

    public DragFrameLayout(@NonNull Context context, @Nullable AttributeSet attrs) {
        this(context, attrs, 0);
    }

    public DragFrameLayout(@NonNull Context context, @Nullable AttributeSet attrs, @AttrRes int defStyleAttr) {
        super(context, attrs, defStyleAttr);
        //第二步：创建存放View的集合
        viewList = new ArrayList<>();

        dragHelper = ViewDragHelper.create(this, 1.0f, new ViewDragHelper.Callback() {

            /**
             * 是否捕获childView:
             * 如果viewList包含child，那么捕获childView
             * 如果不包含child，就不捕获childView
             */
            @Override
            public boolean tryCaptureView(View child, int pointerId) {
                return viewList.contains(child);
            }

            @Override
            public void onViewPositionChanged(View changedView, int left, int top, int dx, int dy) {
                super.onViewPositionChanged(changedView, left, top, dx, dy);
            }

            /**
             * 当捕获到child后的处理：
             * 获取child的监听
             */
            @Override
            public void onViewCaptured(View capturedChild, int activePointerId) {
                super.onViewCaptured(capturedChild, activePointerId);
                if (onDragDropListener != null) {
                    onDragDropListener.onDragDrop(true);
                }
            }

            /**
             * 当释放child后的处理：
             * 取消监听，不再处理
             */
            @Override
            public void onViewReleased(View releasedChild, float xvel, float yvel) {
                super.onViewReleased(releasedChild, xvel, yvel);
                if (onDragDropListener != null) {
                    onDragDropListener.onDragDrop(false);
                }
            }

            /**
             * 到左边界的距离
             */
            @Override
            public int clampViewPositionHorizontal(View child, int left, int dx) {
                return left;
            }

            /**
             * 到上边界的距离
             */
            @Override
            public int clampViewPositionVertical(View child, int top, int dy) {
                return top;
            }
        });
    }

    /**
     * 把要实现拖动的子view添加进来
     * @param view
     */
    public void addDragChildView(View view){
        viewList.add(view);
    }

    @Override
    public boolean onInterceptTouchEvent(MotionEvent ev) {
        //当手指抬起或事件取消的时候 就不拦截事件
        int actionMasked = ev.getActionMasked();
        if (actionMasked == MotionEvent.ACTION_CANCEL || actionMasked == MotionEvent.ACTION_UP) {
            return false;
        }
        return dragHelper.shouldInterceptTouchEvent(ev);
    }

    @Override
    public boolean onTouchEvent(MotionEvent event) {
        dragHelper.processTouchEvent(event);
        return true;
    }
    public interface OnDragDropListener {
        void onDragDrop(boolean captured);
    }

    private OnDragDropListener onDragDropListener;

    public void setOnDragDropListener(OnDragDropListener onDragDropListener) {
        this.onDragDropListener = onDragDropListener;
    }
}

使用方法：

activity_main.xml

<?xml version="1.0" encoding="utf-8"?>
<com.windfindtech.hqdemo.view.DragFrameLayout xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:app="http://schemas.android.com/apk/res-auto"
xmlns:tools="http://schemas.android.com/tools"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:id="@+id/df_content"
tools:context="com.windfindtech.hqdemo.MainActivity">

<ImageView
    android:id="@+id/iv1"
    android:layout_width="100dp"
    android:layout_height="100dp"
    android:src="@mipmap/ic_launcher" />

<TextView
    android:id="@+id/tv1"
    android:layout_width="wrap_content"
    android:layout_height="wrap_content"
    android:layout_gravity="center"
    android:text="可拖拽文字" />
</com.windfindtech.hqdemo.view.DragFrameLayout>

MainActivity.java类

public class MainActivity extends AppCompatActivity {

DragFrameLayout m_dragFrameLayout;
ImageView m_imageView1;
TextView m_textView1;
String TAG = "";

@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_main);
    m_dragFrameLayout = (DragFrameLayout) findViewById(R.id.df_content);
    m_imageView1 = (ImageView)findViewById(R.id.iv1);
    m_textView1 = (TextView) findViewById(R.id.tv1);
//      m_dragFrameLayout.addDragChildView(m_imageView1);
    m_dragFrameLayout.addDragChildView(m_textView1);//具体拖拽动作使用回调即可
}
}