读书 安卓群英传第5章节滑动详解

版权声明：本文为博主原创文章，未经博主允许不得转载。 https://blog.csdn.net/paulkg12/article/details/78385135

安卓群英传第5章节

DragViewTest.app

如果你需要一个正常的build.gradle

apply plugin: 'com.android.application'

android {
    compileSdkVersion 25
    buildToolsVersion "25.0.2"

    defaultConfig {
        applicationId "com.example.android.boardingpass"
        minSdkVersion 10
        targetSdkVersion 25
        versionCode 1
        versionName "1.0"
    }

    buildTypes {
        release {
            minifyEnabled false
        }
    }

}

dependencies {
    compile fileTree(dir: 'libs', include: ['*.jar'])
    compile 'com.android.support:appcompat-v7:25.3.1'
    // COMPLETED (1) Add the compile dependency for the constraint layout support library
    compile 'com.android.support.constraint:constraint-layout:1.0.0-beta4'
}

实现滑动的7种方式

(一和二)layout方式和offsetLeftAndRight（offsetX）

应该知道，view的出现在我们面前的整体流程是：

测量-》布局-》绘制；对应View的measure()->layout()->draw()

在ACTION_DOWN 和ACTION_MOVE的时候使用event.getX()或者event.getRawX()这样的方式取得坐标，再与原来的坐标比较。取差值之后，进行移动即可：如下:

• ==DragView1== 使用的是getX（），其中也提到一个实用的API：offsetLeftAndRight(offsetX)

//
public class DragView1 extends View {

    private int lastX;
    private int lastY;

    public DragView1(Context context) {
        super(context);
        initView();
    }

    public DragView1(Context context, AttributeSet attrs) {
        super(context, attrs);
        initView();
    }

    public DragView1(Context context, AttributeSet attrs, int defStyleAttr) {
        super(context, attrs, defStyleAttr);
        initView();
    }

    private void initView() {
        // 给View设置背景颜色，便于观察
        setBackgroundColor(Color.BLUE);
    }

    // 视图坐标方式
    @Override
    public boolean onTouchEvent(MotionEvent event) {
        int x = (int) event.getX();
        int y = (int) event.getY();
        switch (event.getAction()) {
            case MotionEvent.ACTION_DOWN:
                // 记录触摸点坐标
                lastX = x;
                lastY = y;
                break;
            case MotionEvent.ACTION_MOVE:
                // 计算偏移量
                int offsetX = x - lastX;
                int offsetY = y - lastY;
                // 在当前left、top、right、bottom的基础上加上偏移量
                layout(getLeft() + offsetX,
                        getTop() + offsetY,
                        getRight() + offsetX,
                        getBottom() + offsetY);
//                        offsetLeftAndRight(offsetX);
//                        offsetTopAndBottom(offsetY);
                break;
        }
        return true;
    }
}

• ==DragView2==以下代码则是使用getRawX（）

public class DragView2 extends View {

    private int lastX;
    private int lastY;

    public DragView2(Context context) {
        super(context);
        ininView();
    }

    public DragView2(Context context, AttributeSet attrs) {
        super(context, attrs);
        ininView();
    }

    public DragView2(Context context, AttributeSet attrs, int defStyleAttr) {
        super(context, attrs, defStyleAttr);
        ininView();
    }

    private void ininView() {
        setBackgroundColor(Color.BLUE);
    }

    // 绝对坐标方式
    @Override
    public boolean onTouchEvent(MotionEvent event) {
        int rawX = (int) (event.getRawX());
        int rawY = (int) (event.getRawY());
        switch (event.getAction()) {
            case MotionEvent.ACTION_DOWN:
                // 记录触摸点坐标
                lastX = rawX;
                lastY = rawY;
                break;
            case MotionEvent.ACTION_MOVE:
                // 计算偏移量
                int offsetX = rawX - lastX;
                int offsetY = rawY - lastY;
                // 在当前left、top、right、bottom的基础上加上偏移量
                layout(getLeft() + offsetX,
                        getTop() + offsetY,
                        getRight() + offsetX,
                        getBottom() + offsetY);
                // 重新设置初始坐标
                lastX = rawX;
                lastY = rawY;
                break;
        }
        return true;
    }
}

（三）LayoutParams的方式（DragView3.java）

主要就是setLayoutParams(layoutParams)了

public class DragView3 extends View {

    private int lastX;
    private int lastY;

    public DragView3(Context context) {
        super(context);
        ininView();
    }

    public DragView3(Context context, AttributeSet attrs) {
        super(context, attrs);
        ininView();
    }

    public DragView3(Context context, AttributeSet attrs, int defStyleAttr) {
        super(context, attrs, defStyleAttr);
        ininView();
    }

    private void ininView() {
        setBackgroundColor(Color.BLUE);
    }

    @Override
    public boolean onTouchEvent(MotionEvent event) {
        int x = (int) event.getX();
        int y = (int) event.getY();
        switch (event.getAction()) {
            case MotionEvent.ACTION_DOWN:
                // 记录触摸点坐标
                lastX = (int) event.getX();
                lastY = (int) event.getY();
                break;
            case MotionEvent.ACTION_MOVE:
                // 计算偏移量
                int offsetX = x - lastX;
                int offsetY = y - lastY;
                ViewGroup.MarginLayoutParams layoutParams = (ViewGroup.MarginLayoutParams) getLayoutParams();
//                LinearLayout.LayoutParams layoutParams = (LinearLayout.LayoutParams) getLayoutParams();
                layoutParams.leftMargin = getLeft() + offsetX;
                layoutParams.topMargin = getTop() + offsetY;
                setLayoutParams(layoutParams);
                break;
        }
        return true;
    }
}

（四）scrollTo()和scrollBy()(DragView4.java)

public class DragView4 extends View {

    private int lastX;
    private int lastY;

    public DragView4(Context context) {
        super(context);
        ininView();
    }

    public DragView4(Context context, AttributeSet attrs) {
        super(context, attrs);
        ininView();
    }

    public DragView4(Context context, AttributeSet attrs, int defStyleAttr) {
        super(context, attrs, defStyleAttr);
        ininView();
    }

    private void ininView() {
        setBackgroundColor(Color.BLUE);
    }

    @Override
    public boolean onTouchEvent(MotionEvent event) {
        int x = (int) event.getX();
        int y = (int) event.getY();
        switch (event.getAction()) {
            case MotionEvent.ACTION_DOWN:
                lastX = (int) event.getX();
                lastY = (int) event.getY();
                break;
            case MotionEvent.ACTION_MOVE:
                int offsetX = x - lastX;
                int offsetY = y - lastY;
                ((View) getParent()).scrollBy(-offsetX, -offsetY);
                break;
        }
        return true;
    }
}

(五)Scroller

public class DragView5 extends View {

    private int lastX;
    private int lastY;
    private Scroller mScroller;

    public DragView5(Context context) {
        super(context);
        ininView(context);
    }

    public DragView5(Context context, AttributeSet attrs) {
        super(context, attrs);
        ininView(context);
    }

    public DragView5(Context context, AttributeSet attrs, int defStyleAttr) {
        super(context, attrs, defStyleAttr);
        ininView(context);
    }

    private void ininView(Context context) {
        setBackgroundColor(Color.BLUE);
        // 初始化Scroller
        mScroller = new Scroller(context);
    }

    @Override
    public void computeScroll() {
        super.computeScroll();
        // 判断Scroller是否执行完毕
        if (mScroller.computeScrollOffset()) {
            ((View) getParent()).scrollTo(
                    mScroller.getCurrX(),
                    mScroller.getCurrY());
            // 通过重绘来不断调用computeScroll
            invalidate();
        }
    }

    @Override
    public boolean onTouchEvent(MotionEvent event) {
        int x = (int) event.getX();
        int y = (int) event.getY();
        switch (event.getAction()) {
            case MotionEvent.ACTION_DOWN:
                lastX = (int) event.getX();
                lastY = (int) event.getY();
                break;
            case MotionEvent.ACTION_MOVE:
                int offsetX = x - lastX;
                int offsetY = y - lastY;
                ((View) getParent()).scrollBy(-offsetX, -offsetY);
                break;
            case MotionEvent.ACTION_UP:
                // 手指离开时，执行滑动过程
                //我试过，如果把这一段的代码释掉，就不能实现归位功能了。
                View viewGroup = ((View) getParent());
                mScroller.startScroll(
                        viewGroup.getScrollX(),
                        viewGroup.getScrollY(),
                        -viewGroup.getScrollX(),
                        -viewGroup.getScrollY());
                invalidate();
                break;
        }
        return true;
    }
}

（六）属性动画

见其他博文

（七）ViewDragHelper

强大类库

public class DragViewGroup extends FrameLayout {

    private ViewDragHelper mViewDragHelper;
    private View mMenuView, mMainView;
    private int mWidth;

    public DragViewGroup(Context context) {
        super(context);
        initView();
    }

    public DragViewGroup(Context context, AttributeSet attrs) {
        super(context, attrs);
        initView();
    }

    public DragViewGroup(Context context,
                         AttributeSet attrs, int defStyleAttr) {
        super(context, attrs, defStyleAttr);
        initView();
    }

    @Override
    protected void onFinishInflate() {
        super.onFinishInflate();
        mMenuView = getChildAt(0);
        mMainView = getChildAt(1);
    }

    @Override
    protected void onSizeChanged(int w, int h, int oldw, int oldh) {
        super.onSizeChanged(w, h, oldw, oldh);
        mWidth = mMenuView.getMeasuredWidth();
    }

    @Override
    public boolean onInterceptTouchEvent(MotionEvent ev) {
        return mViewDragHelper.shouldInterceptTouchEvent(ev);
    }

    @Override
    public boolean onTouchEvent(MotionEvent event) {
        //将触摸事件传递给ViewDragHelper,此操作必不可少
        mViewDragHelper.processTouchEvent(event);
        return true;
    }

    private void initView() {
        mViewDragHelper = ViewDragHelper.create(this, callback);
    }

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

                // 何时开始检测触摸事件
                @Override
                public boolean tryCaptureView(View child, int pointerId) {
                    //如果当前触摸的child是mMainView时开始检测
                    return mMainView == child;
                }

                // 触摸到View后回调
                @Override
                public void onViewCaptured(View capturedChild,
                                           int activePointerId) {
                    super.onViewCaptured(capturedChild, activePointerId);
                }

                // 当拖拽状态改变，比如idle，dragging
                @Override
                public void onViewDragStateChanged(int state) {
                    super.onViewDragStateChanged(state);
                }

                // 当位置改变的时候调用,常用与滑动时更改scale等
                @Override
                public void onViewPositionChanged(View changedView,
                                                  int left, int top, int dx, int dy) {
                    super.onViewPositionChanged(changedView, left, top, dx, dy);
                }

                // 处理垂直滑动
                @Override
                public int clampViewPositionVertical(View child, int top, int dy) {
                    return 0;
                }

                // 处理水平滑动
                @Override
                public int clampViewPositionHorizontal(View child, int left, int dx) {
                    return left;
                }

                // 拖动结束后调用
                @Override
                public void onViewReleased(View releasedChild, float xvel, float yvel) {
                    super.onViewReleased(releasedChild, xvel, yvel);
                    //手指抬起后缓慢移动到指定位置
                    if (mMainView.getLeft() < 500) {
                        //关闭菜单
                        //相当于Scroller的startScroll方法
                        mViewDragHelper.smoothSlideViewTo(mMainView, 0, 0);
                        ViewCompat.postInvalidateOnAnimation(DragViewGroup.this);
                    } else {
                        //打开菜单
                        mViewDragHelper.smoothSlideViewTo(mMainView, 300, 0);
                        ViewCompat.postInvalidateOnAnimation(DragViewGroup.this);
                    }
                }
            };

    @Override
    public void computeScroll() {
        if (mViewDragHelper.continueSettling(true)) {
            ViewCompat.postInvalidateOnAnimation(this);
        }
    }
}

？何时与xml关联的？

A：首先xml如下

<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:tools="http://schemas.android.com/tools"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:paddingLeft="@dimen/activity_horizontal_margin"
    android:paddingRight="@dimen/activity_horizontal_margin"
    android:paddingTop="@dimen/activity_vertical_margin"
    android:paddingBottom="@dimen/activity_vertical_margin"
    tools:context=".MainActivity">

    <com.imooc.dragviewtest.DragViewGroup
        android:layout_width="match_parent"
        android:layout_height="match_parent"
        android:id="@+id/view">

        <FrameLayout
            android:layout_width="match_parent"
            android:layout_height="match_parent"
            android:background="@android:color/holo_blue_light">

            <Button
                android:layout_width="wrap_content"
                android:layout_height="wrap_content"
                android:text="Menu" />
        </FrameLayout>

        <FrameLayout
            android:layout_width="match_parent"
            android:layout_height="match_parent"
            android:background="@android:color/holo_orange_dark">

            <Button
                android:layout_width="wrap_content"
                android:layout_height="wrap_content"
                android:text="Main" />
        </FrameLayout>
    </com.imooc.dragviewtest.DragViewGroup>
</RelativeLayout>

于是我们的答案是：在xml显然显式地引用了com.imooc.dragviewtest.DragViewGroup这个java.class

总结图片，图像让你记忆更加深刻