防QQ侧滑条目

每当我们看到侧滑的时候就会不由自主的想到ViewDragHelper,下面我将给大家来介绍关于ViewDragHelper的用法，以及自定义控件中需要注意的点；

ViewDragHelper的使用方法，分为以下几个步骤；

第一步是创建类，继承ViewGrup，建立布局

<?xml version="1.0" encoding="utf-8"?>
<com.example.selfviewdemo.ViewDragHelperTest
xmlns:android="http://schemas.android.com/apk/res/android"
android:id="@+id/swipeLayout"
android:layout_width="match_parent"
android:layout_height="wrap_content">

<LinearLayout
android:layout_width="50dp"
android:layout_height="50dp"
android:gravity="center_vertical">

<ImageView
android:id="@+id/imageView"
android:layout_width="50dp"
android:layout_height="50dp"
android:layout_marginLeft="8dp"
android:layout_marginRight="8dp"
android:src="@mipmap/ic_launcher"/>

<TextView
android:id="@+id/textView"
android:layout_width="wrap_content"
android:layout_height="match_parent"
android:gravity="center_vertical"
android:text="@string/nihao"
android:textColor="#444"
android:textSize="18sp"/>
</LinearLayout>

<LinearLayout
android:layout_width="140dp"
android:layout_height="50dp">

<TextView
android:layout_width
4000
="70dp"
android:layout_height="match_parent"
android:background="#ccc"
android:gravity="center"
android:text="置顶"
android:textColor="#fff"/>

<TextView
android:id="@+id/tv_del"
android:layout_width="70dp"
android:layout_height="match_parent"
android:background="#f00"
android:clickable="true"
android:gravity="center"
android:text="刪除"
android:textColor="#fff"/>
</LinearLayout>
</com.example.selfviewdemo.ViewDragHelperTest>

第二步初始化ViewDragHelper

ViewDragHelper viewDragHelper = ViewDragHelper.create(this, new MyCallbak());

第三步拦截事件，这一点非常重要，因为很多新手在做这一步的时候总会忘了他。当然忘记的后果就是没法收到手势事件。而处理方法很简单只需加两行固定的代码就行了。

@Override
public boolean onInterceptTouchEvent(MotionEvent ev) {
//拦截事件给ViewDragHelper
return dragHelper.shouldInterceptTouchEvent(ev);
}
@Override
public boolean onTouchEvent(MotionEvent event) {
dragHelper.processTouchEvent(event);
//自己处理此事件；
return true;
}

第四步得到viewgrup中的子控件对象，也是固定代码

@Override
protected void onFinishInflate() {
super.onFinishInflate();
contentlayout = getChildAt(0);//内容区域
deletelayout = getChildAt(1);//侧滑菜单

//得到布局的宽高;
mContentheight = contentlayout.getLayoutParams().height;
mDeletewidth = deletelayout.getLayoutParams().width;
mDeleteheight = deletelayout.getLayoutParams().height;

}

第五步，测量，和布局控件

第六步，实现ViewDragHelper.Callback()；里面几个重要的方法如下：

//这里判断当前的滑动控件；
@Override
public boolean tryCaptureView(View child, int pointerId) {}
//这里是水平方向上做滑动；
@Override
public int clampViewPositionHorizontal(View child, int left, int dx) {}
//当控件位子改变时调用，这里的left是当前滑动子控件的左边距离父控件左边的坐标距离（在父左边为负在右边为正）
@Override
public void onViewPositionChanged(View changedView, int left, int top, int dx, int dy) {}
//当手指离开控件时调用。
@Override
public void onViewReleased(View releasedChild, float xvel, float yvel) {
//首先要得到子控件的x坐标；
int content_dx = contentlayout.getLeft();
//再根据子控件的x坐标进行判断位子。最后调用一下动画到所要到的子定位置；
ViewDragHelper.smoothSlideViewTo(View view,x,y);
view 为所需要动画的View对象，
“x，y”分别为指定该控件要到达的“左，上”坐标值；
}

最后为了动画加上一段代码让其动画看上去更加的流畅。代码如下：直接粘贴复制就行了，这是一段固定代码；

// 持续平滑动画 高频调用
public void computeScroll() {
// 如果返回true，动画还需要继续
if (dragHelper.continueSettling(true)) {
ViewCompat.postInvalidateOnAnimation(this);
}
}

完整代码如下：

package com.example.selfviewdemo;

import android.content.Context;
import android.graphics.Rect;
import android.support.v4.view.ViewCompat;
import android.support.v4.widget.ViewDragHelper;
import android.util.AttributeSet;
import android.util.Log;
import android.view.MotionEvent;
import android.view.View;
import android.widget.LinearLayout;

/**
* Created by yuchao on 17/2/10.
*/
public class ViewDragHelperTest extends LinearLayout {

private static final String TAG = ViewDragHelperTest.class.getSimpleName();
private ViewDragHelper dragHelper;
private View contentlayout;
private View deletelayout;
private int mContentheight;
private int mDeletewidth;
private int mDeleteheight;

public ViewDragHelperTest(Context context) {
this(context, null);
}

public ViewDragHelperTest(Context context, AttributeSet attrs) {
this(context, attrs, 0);
}

public ViewDragHelperTest(Context context, AttributeSet attrs, int defStyleAttr) {
super(context, attrs, defStyleAttr);
dragHelper = ViewDragHelper.create(this, mCallback);
}

@Override
protected void onFinishInflate() {
super.onFinishInflate();
contentlayout = getChildAt(0);//内容区域
deletelayout = getChildAt(1);//侧滑菜单

//得到布局的宽高;
mContentheight = contentlayout.getLayoutParams().height;
mDeletewidth = deletelayout.getLayoutParams().width;
mDeleteheight = deletelayout.getLayoutParams().height;

}

@Override
protected void onMeasure(int widthMeasureSpec, int heightMeasureSpec) {
super.onMeasure(widthMeasureSpec, heightMeasureSpec);
Log.d(TAG, "onMeasure: mDeletewidth = " + mDeletewidth);
//1.测量content
int contentHight = MeasureSpec.makeMeasureSpec(mContentheight, MeasureSpec.EXACTLY);
contentlayout.measure(widthMeasureSpec, contentHight);
//1.测量delete
int deleteHight = MeasureSpec.makeMeasureSpec(mDeleteheight, MeasureSpec.EXACTLY);
int deleteWidth = MeasureSpec.makeMeasureSpec(mDeletewidth, MeasureSpec.EXACTLY);
deletelayout.measure(deleteWidth, deleteHight);

//setMeasuredDimension(widthMeasureSpec, contentHight);
setMeasuredDimension(widthMeasureSpec, contentHight);
}

@Override
protected void onLayout(boolean changed, int l, int t, int r, int b) {
super.onLayout(changed, l, t, r, b);
Log.d(TAG, "onLayout: enter");
int dx = 0;
contentlayout.layout(0 - dx, 0, contentlayout.getMeasuredWidth(), contentlayout.getMeasuredHeight());

deletelayout.layout(contentlayout.getMeasuredWidth() - dx, 0,
contentlayout.getMeasuredWidth() + deletelayout.getMeasuredWidth() - dx
, deletelayout.getMeasuredHeight());
}

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

@Override
public boolean tryCaptureView(View child, int pointerId) {
return true;
}

@Override
public int clampViewPositionHorizontal(View child, int left, int dx) {
if (child == contentlayout) {
if (left > 0) {
return 0;
} else if (left < -mDeletewidth) {
return -mDeletewidth;
}
} else if (child == deletelayout) {
if (left > contentlayout.getMeasuredWidth()) {
return contentlayout.getMeasuredWidth();
} else if (left < contentlayout.getMeasuredWidth() - mDeletewidth) {
return contentlayout.getMeasuredWidth() - mDeletewidth;
}
}
return left;
}

@Override
public void onViewPositionChanged(View changedView, int left, int top, int dx, int dy) {
super.onViewPositionChanged(changedView, left, top, dx, dy);
//移动内容
if (changedView == contentlayout) {
//改变删除组件的位置
int deleteleft = contentlayout.getMeasuredWidth() + left;
int deletetop = 0;
int deleteright = deleteleft + deletelayout.getMeasuredWidth();
int deletebottom = deletelayout.getMeasuredHeight();
deletelayout.layout(deleteleft, deletetop, deleteright, deletebottom);
} else if (changedView == deletelayout) {
int contentLeft = left - contentlayout.getMeasuredWidth();
int contentTop = 0;

a06b
int contentRight = contentLeft + contentlayout.getMeasuredWidth();
int contentbotton = contentlayout.getMeasuredHeight();
contentlayout.layout(contentLeft, contentTop, contentRight, contentbotton);
}
}

@Override
public void onViewReleased(View releasedChild, float xvel, float yvel) {
super.onViewReleased(releasedChild, xvel, yvel);
//松开手;
//得到contentlayout的X坐标;
int content_dx = contentlayout.getLeft();
if (content_dx < -deletelayout.getMeasuredWidth() / 2) {
dragHelper.smoothSlideViewTo(contentlayout, -deletelayout.getMeasuredWidth(), 0);
dragHelper.smoothSlideViewTo(deletelayout, contentlayout.getMeasuredWidth() - deletelayout.getMeasuredWidth(), 0);
invalidate();
} else {
dragHelper.smoothSlideViewTo(contentlayout, 0, 0);
dragHelper.smoothSlideViewTo(deletelayout, contentlayout.getMeasuredWidth(), 0);
invalidate();
}
}
};

// 持续平滑动画 高频调用
public void computeScroll() {
// 如果返回true，动画还需要继续
if (dragHelper.continueSettling(true)) {
ViewCompat.postInvalidateOnAnimation(this);
}
}

@Override
public boolean onInterceptTouchEvent(MotionEvent ev) {
return dragHelper.shouldInterceptTouchEvent(ev);
}
@Override
public boolean onTouchEvent(MotionEvent event) {
dragHelper.processTouchEvent(event);
return true;
}

}

有什么不足的地方希望能给出一些建议！感谢!