ViewDragHelper实战自己打造Drawerlayout

本文主要是介绍ViewDragHelper实战自己打造Drawerlayout，希望对大家解决编程问题提供一定的参考价值，需要的开发者们随着小编来一起学习吧！

分享一下我老师大神的人工智能教程！零基础，通俗易懂！http://blog.csdn.net/jiangjunshow

也欢迎大家转载本篇文章。分享知识，造福人民，实现我们中华民族伟大复兴！

转载请标明出处：
http://blog.csdn.net/lmj623565791/article/details/47396187；
本文出自:【张鸿洋的博客】

一、概述

中间拖了蛮长时间了，在上一篇我们介绍了ViewDragHelper，详情：ViewDragHelper完全解析，当然了，上一篇都是小示例的形式去演示代码功能，并不能给人一种实用的感觉。那么，本篇博客就准备实用ViewDragHelper来实现一个DrawerLayout的效果，当然了，大家也可以选择直接去看Drawerlayout的源码。相信侧滑大家肯定不陌生，网络上流传无数个版本，其实利用ViewDragHelper就能方便的写出比较不错的侧滑代码~

那么首先上个效果图：

ok，其实和DrawerLayout效果类似，当然不是完全的一致~~本篇的主要目的也是演示VDH的实战用法，大家在选择侧滑的时候还是建议使用DrawerLayout.

二、实战

(一)布局文件

首先看一下布局文件:

<com.zhy.learn.view.LeftDrawerLayout xmlns:android="http://schemas.android.com/apk/res/android"xmlns:tools="http://schemas.android.com/tools"                                   android:layout_width="match_parent"android:id="@+id/id_drawerlayout"                                     android:layout_height="match_parent"    >    <!--content-->    <RelativeLayout        android:clickable="true"        android:layout_width="match_parent"        android:background="#44ff0000"        android:layout_height="match_parent">        <TextView            android:id="@+id/id_content_tv"            android:layout_width="wrap_content"            android:layout_height="wrap_content"            android:text="hello world"            android:textSize="40sp"            android:layout_centerInParent="true"/>    </RelativeLayout>    <!--menu-->    <FrameLayout        android:id="@+id/id_container_menu"        android:layout_width="match_parent"        android:layout_height="match_parent"        >    </FrameLayout></com.zhy.learn.view.LeftDrawerLayout>1
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ok，可以看到我们的LeftDrawerLayout里面一个是content，一个是menu~为了方便，我们就默认child0为content，child1为menu。

（二）LeftDrawerLayout

package com.zhy.learn.view;import android.content.Context;import android.support.v4.widget.ViewDragHelper;import android.util.AttributeSet;import android.view.MotionEvent;import android.view.View;import android.view.ViewGroup;import com.zhy.util.common.L;/** * Created by zhy on 15/5/29. */public class LeftDrawerLayout extends ViewGroup{    private static final int MIN_DRAWER_MARGIN = 64; // dp    /**     * Minimum velocity that will be detected as a fling     */    private static final int MIN_FLING_VELOCITY = 400; // dips per second    /**     * drawer离父容器右边的最小外边距     */    private int mMinDrawerMargin;    private View mLeftMenuView;    private View mContentView;    private ViewDragHelper mHelper;    /**     * drawer显示出来的占自身的百分比     */    private float mLeftMenuOnScrren;    public LeftDrawerLayout(Context context, AttributeSet attrs)    {        super(context, attrs);        //setup drawer's minMargin        final float density = getResources().getDisplayMetrics().density;        final float minVel = MIN_FLING_VELOCITY * density;        mMinDrawerMargin = (int) (MIN_DRAWER_MARGIN * density + 0.5f);        mHelper = ViewDragHelper.create(this, 1.0f, new ViewDragHelper.Callback()        {            @Override            public int clampViewPositionHorizontal(View child, int left, int dx)            {                int newLeft = Math.max(-child.getWidth(), Math.min(left, 0));                return newLeft;            }            @Override            public boolean tryCaptureView(View child, int pointerId)            {                L.e("tryCaptureView");                return child == mLeftMenuView;            }            @Override            public void onEdgeDragStarted(int edgeFlags, int pointerId)            {                L.e("onEdgeDragStarted");                mHelper.captureChildView(mLeftMenuView, pointerId);            }            @Override            public void onViewReleased(View releasedChild, float xvel, float yvel)            {                L.e("onViewReleased");                final int childWidth = releasedChild.getWidth();                float offset = (childWidth + releasedChild.getLeft()) * 1.0f / childWidth;                mHelper.settleCapturedViewAt(xvel > 0 || xvel == 0 && offset > 0.5f ? 0 : -childWidth, releasedChild.getTop());                invalidate();            }            @Override            public void onViewPositionChanged(View changedView, int left, int top, int dx, int dy)            {                final int childWidth = changedView.getWidth();                float offset = (float) (childWidth + left) / childWidth;                mLeftMenuOnScrren = offset;                //offset can callback here                 changedView.setVisibility(offset == 0 ? View.INVISIBLE : View.VISIBLE);                invalidate();            }            @Override            public int getViewHorizontalDragRange(View child)            {                return mLeftMenuView == child ? child.getWidth() : 0;            }        });        //设置edge_left track        mHelper.setEdgeTrackingEnabled(ViewDragHelper.EDGE_LEFT);        //设置minVelocity        mHelper.setMinVelocity(minVel);    }    @Override    protected void onMeasure(int widthMeasureSpec, int heightMeasureSpec)    {        int widthSize = MeasureSpec.getSize(widthMeasureSpec);        int heightSize = MeasureSpec.getSize(heightMeasureSpec);        setMeasuredDimension(widthSize, heightSize);        View leftMenuView = getChildAt(1);        MarginLayoutParams lp = (MarginLayoutParams)                leftMenuView.getLayoutParams();        final int drawerWidthSpec = getChildMeasureSpec(widthMeasureSpec,                mMinDrawerMargin + lp.leftMargin + lp.rightMargin,                lp.width);        final int drawerHeightSpec = getChildMeasureSpec(heightMeasureSpec,                lp.topMargin + lp.bottomMargin,                lp.height);        leftMenuView.measure(drawerWidthSpec, drawerHeightSpec);        View contentView = getChildAt(0);        lp = (MarginLayoutParams) contentView.getLayoutParams();        final int contentWidthSpec = MeasureSpec.makeMeasureSpec(                widthSize - lp.leftMargin - lp.rightMargin, MeasureSpec.EXACTLY);        final int contentHeightSpec = MeasureSpec.makeMeasureSpec(                heightSize - lp.topMargin - lp.bottomMargin, MeasureSpec.EXACTLY);        contentView.measure(contentWidthSpec, contentHeightSpec);        mLeftMenuView = leftMenuView;        mContentView = contentView;    }    @Override    protected void onLayout(boolean changed, int l, int t, int r, int b)    {        View menuView = mLeftMenuView;        View contentView = mContentView;        MarginLayoutParams lp = (MarginLayoutParams) contentView.getLayoutParams();        contentView.layout(lp.leftMargin, lp.topMargin,                lp.leftMargin + contentView.getMeasuredWidth(),                lp.topMargin + contentView.getMeasuredHeight());        lp = (MarginLayoutParams) menuView.getLayoutParams();        final int menuWidth = menuView.getMeasuredWidth();        int childLeft = -menuWidth + (int) (menuWidth * mLeftMenuOnScrren);        menuView.layout(childLeft, lp.topMargin, childLeft + menuWidth,                lp.topMargin + menuView.getMeasuredHeight());    }    @Override    public boolean onInterceptTouchEvent(MotionEvent ev)    {        boolean shouldInterceptTouchEvent = mHelper.shouldInterceptTouchEvent(ev);        return shouldInterceptTouchEvent;    }    @Override    public boolean onTouchEvent(MotionEvent event)    {        mHelper.processTouchEvent(event);        return true;    }    @Override    public void computeScroll()    {        if (mHelper.continueSettling(true))        {            invalidate();        }    }    public void closeDrawer()    {        View menuView = mLeftMenuView;        mLeftMenuOnScrren = 0.f;        mHelper.smoothSlideViewTo(menuView, -menuView.getWidth(), menuView.getTop());    }    public void openDrawer()    {        View menuView = mLeftMenuView;        mLeftMenuOnScrren = 1.0f;        mHelper.smoothSlideViewTo(menuView, 0, menuView.getTop());    }    @Override    protected LayoutParams generateDefaultLayoutParams()    {        return new MarginLayoutParams(LayoutParams.MATCH_PARENT, LayoutParams.MATCH_PARENT);    }    public LayoutParams generateLayoutParams(AttributeSet attrs)    {        return new MarginLayoutParams(getContext(), attrs);    }    protected LayoutParams generateLayoutParams(ViewGroup.LayoutParams p)    {        return new MarginLayoutParams(p);    }}1
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哈，很少的代码就完成了我们的侧滑的编写，目测如果使用横向的LinearLayout代码更短。构造方法中，主要就是初始化我们的mDragHelper了，接下来onMeasure和onLayout都比较简单，onLayout也只是去将我们的menu设置到屏幕的左侧以至于不可见。onInterceptTouchEvent和onTouchEvent中都只需要简单的调用mDragHelper的方法。那么核心代码都在我们的ViewDragHelper.Callback的实例中了。注意一点：我们LeftDrawerLayout默认的LayoutParams为MarginLayoutParams，注意复写相关方法。

接下来就把注意力放到我们的Callback中，我尽可能的按照调用的逻辑来解释各个方法：

onEdgeDragStarted 如果你仔细的看过上篇，那么一定知道这个方法的回调位置；因为我们的View不可见，所以我们没有办法直接通过触摸到它来把menu设置为captureView，所以我们只能设置边界检测，当MOVE时回调onEdgeDragStarted时，我们直接通过captureChildView手动捕获。
tryCaptureView 那么既然我们手动捕获了，为什么还需要这个方法呢？主要是因为当Drawer拉出的时候，我们通过拖拽Drawer也能进行移动菜单。
clampViewPositionHorizontal 主要是移动的时候去控制控制范围，可以看到我们的int newLeft = Math.max(-child.getWidth(), Math.min(left, 0));一定>=-child.getWidth() && <=0 。
getViewHorizontalDragRange 为什么要复写，我们上篇已经描述过，返回captureView的移动范围。
onViewReleased 则是释放的时候触发的，我们计算当前显示的百分比，以及加速度来决定是否显示drawer，从代码可以看出，当xvel > 0 || xvel == 0 && offset > 0.5f显示我们的菜单，其他情况隐藏。这里注意一点xvel的值只有大于我们设置的minVelocity才会出现大于0，如果小于我们设置的值则一直是0。
onViewPositionChanged 整个pos变化的过程中，我们计算offset保存，这里可以使用接口将offset回调出去，方便做动画。

ok，我们重写的所有方法描述完成了~那么博文主要内容也就结束了~哈~是不是 so easy ~!

呃，忘了MainActivity和Fragment的代码了~~按顺序贴

（三）LeftDrawerLayoutActivity

package com.imooc.testandroid;import android.os.Bundle;import android.support.v4.app.FragmentManager;import android.support.v7.app.ActionBarActivity;import android.view.Menu;import android.view.MenuItem;import android.widget.TextView;import com.zhy.learn.view.LeftDrawerLayout;public class LeftDrawerLayoutActivity extends ActionBarActivity{    private LeftMenuFragment mMenuFragment;    private LeftDrawerLayout mLeftDrawerLayout ;    private TextView mContentTv ;    @Override    protected void onCreate(Bundle savedInstanceState)    {        super.onCreate(savedInstanceState);        setContentView(R.layout.activity_left_drawer_layout);        mLeftDrawerLayout = (LeftDrawerLayout) findViewById(R.id.id_drawerlayout);        mContentTv = (TextView) findViewById(R.id.id_content_tv);        FragmentManager fm = getSupportFragmentManager();        mMenuFragment = (LeftMenuFragment) fm.findFragmentById(R.id.id_container_menu);        if (mMenuFragment == null)        {            fm.beginTransaction().add(R.id.id_container_menu, mMenuFragment = new LeftMenuFragment()).commit();        }        mMenuFragment.setOnMenuItemSelectedListener(new LeftMenuFragment.OnMenuItemSelectedListener()        {            @Override            public void menuItemSelected(String title)            {                mLeftDrawerLayout.closeDrawer();                mContentTv.setText(title);            }        });    }1
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可以看到drawer使用了一个Fragment ~~

(四) LeftMenuFragment

import android.os.Bundle;import android.support.annotation.Nullable;import android.support.v4.app.ListFragment;import android.view.LayoutInflater;import android.view.View;import android.view.ViewGroup;import android.widget.ListView;/** * Created by zhy on 15/4/26. */public class LeftMenuFragment extends ListFragment {    private static final int SIZE_MENU_ITEM = 3;    private MenuItem[] mItems = new MenuItem[SIZE_MENU_ITEM];    private LeftMenuAdapter mAdapter;    private LayoutInflater mInflater;    @Override    public void onCreate(@Nullable Bundle savedInstanceState) {        super.onCreate(savedInstanceState);        mInflater = LayoutInflater.from(getActivity());        MenuItem menuItem = null;        for (int i = 0; i < SIZE_MENU_ITEM; i++) {            menuItem = new MenuItem(getResources().getStringArray(R.array.array_left_menu)[i], false, R.drawable.music_36px, R.drawable.music_36px_light);            mItems[i] = menuItem;        }    }    @Override    public View onCreateView(LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState) {        return super.onCreateView(inflater, container, savedInstanceState);    }    @Override    public void onViewCreated(View view, @Nullable Bundle savedInstanceState) {        super.onViewCreated(view, savedInstanceState);        view.setBackgroundColor(0xffffffff);        setListAdapter(mAdapter = new LeftMenuAdapter(getActivity(), mItems));    }    @Override    public void onListItemClick(ListView l, View v, int position, long id) {        super.onListItemClick(l, v, position, id);        if (mMenuItemSelectedListener != null) {            mMenuItemSelectedListener.menuItemSelected(((MenuItem) getListAdapter().getItem(position)).text);        }        mAdapter.setSelected(position);    }    //选择回调的接口    public interface OnMenuItemSelectedListener {        void menuItemSelected(String title);    }    private OnMenuItemSelectedListener mMenuItemSelectedListener;    public void setOnMenuItemSelectedListener(OnMenuItemSelectedListener menuItemSelectedListener) {        this.mMenuItemSelectedListener = menuItemSelectedListener;    }}public class MenuItem{    public MenuItem(String text, boolean isSelected, int icon, int iconSelected) {        this.text = text;        this.isSelected = isSelected;        this.icon = icon;        this.iconSelected = iconSelected;    }    boolean isSelected;    String text;    int icon;    int iconSelected;}/** * Created by zhy on 15/4/26. */public class LeftMenuAdapter extends ArrayAdapter<MenuItem> {    private LayoutInflater mInflater;    private int mSelected;    public LeftMenuAdapter(Context context, MenuItem[] objects) {        super(context, -1, objects);        mInflater = LayoutInflater.from(context);    }    @Override    public View getView(int position, View convertView, ViewGroup parent) {        if (convertView == null) {            convertView = mInflater.inflate(R.layout.item_left_menu, parent, false);        }        ImageView iv = (ImageView) convertView.findViewById(R.id.id_item_icon);        TextView title = (TextView) convertView.findViewById(R.id.id_item_title);        title.setText(getItem(position).text);        iv.setImageResource(getItem(position).icon);        convertView.setBackgroundColor(Color.TRANSPARENT);        if (position == mSelected) {            iv.setImageResource(getItem(position).iconSelected);            convertView.setBackgroundColor(getContext().getResources().getColor(R.color.state_menu_item_selected));        }        return convertView;    }    public void setSelected(int position) {        this.mSelected = position;        notifyDataSetChanged();    }}1
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