Android中的Banner效果

第一步：
package com.example.example;

import android.content.Context;
import android.os.Handler;
import android.os.Message;
import android.util.AttributeSet;
import android.util.Log;
import android.view.MotionEvent;
import android.view.View;
import android.view.ViewGroup;
import android.view.animation.DecelerateInterpolator;
import android.widget.Scroller;

public class BannerLayout extends ViewGroup {

    private Scroller scroller;
    private float mLastMotionX;
    // private int mTouchSlop;

    private OnItemClickListener onItemClickListener;

    private int currentScreenIndex = 0;

    private boolean moving = false;

    private boolean autoScroll = false;

    private int scrollTime = 4 * 1000;

    private int currentWhat = 0;

    private Handler handler = new Handler() {
        @Override
        public void handleMessage(Message msg) {
            if (autoScroll && currentWhat == msg.what) {
                currentScreenIndex = (currentScreenIndex + 1) % getChildCount();
                scrollToScreen(currentScreenIndex);

                Log.i("TAG", "handleMessage scrollToScreen:"
                        + currentScreenIndex);

                if (autoScroll)
                    handler.sendEmptyMessageDelayed(currentWhat, scrollTime);
            }
        }
    };

    public BannerLayout(Context context) {
        super(context);

        initView(context);
        // TODO Auto-generated constructor stub
    }

    public BannerLayout(Context context, AttributeSet attrs, int defStyle) {
        super(context, attrs, defStyle);
        // TODO Auto-generated constructor stub
        initView(context);
    }

    public BannerLayout(Context context, AttributeSet attrs) {
        super(context, attrs);
        initView(context);
        // TODO Auto-generated constructor stub
    }

    private void initView(final Context context) {
        this.scroller = new Scroller(context, new DecelerateInterpolator(4));// OvershootInterpolator(1.1f)

        // handler.sendEmptyMessageDelayed(currentWhat, scrollTime);

        // final ViewConfiguration configuration = ViewConfiguration
        // .get(getContext());
        // mTouchSlop = configuration.getScaledTouchSlop();
    }

    @Override
    protected void onMeasure(int widthMeasureSpec, int heightMeasureSpec) {
        // super.onMeasure(widthMeasureSpec, heightMeasureSpec);

        int maxHeight = -1;

        final int count = getChildCount();
        for (int i = 0; i < count; i++) {
            getChildAt(i).measure(widthMeasureSpec, heightMeasureSpec);

            maxHeight = Math.max(maxHeight, getChildAt(i).getMeasuredHeight());

        }
        maxHeight = Math.min(maxHeight, MeasureSpec.getSize(heightMeasureSpec));

        Log.e("TAG", "onMeasure Height:" + maxHeight);

        setMeasuredDimension(MeasureSpec.getSize(widthMeasureSpec), maxHeight);
    }

    @Override
    protected void onLayout(boolean changed, int left, int top, int right,
            int bottom) {

        final int count = getChildCount();

        int cLeft = 0;

        for (int i = 0; i < count; i++) {
            View child = getChildAt(i);
            if (child.getVisibility() == View.GONE)
                continue;

            // child.setVisibility(View.VISIBLE);
            final int childWidth = child.getMeasuredWidth();
            child.layout(cLeft, 0, cLeft + childWidth,
                    child.getMeasuredHeight());

            cLeft += childWidth;
        }
    }

    @Override
    public void computeScroll() {
        if (scroller.computeScrollOffset()) {
            scrollTo(scroller.getCurrX(), 0);
            postInvalidate();
        }
    }

    @Override
    public boolean onTouchEvent(MotionEvent ev) {
        if (getChildCount() == 0)
            return false;
        final int action = ev.getAction();
        final float x = ev.getX();
        switch (action) {
        case MotionEvent.ACTION_DOWN:

            autoScroll = false;

            currentWhat++;

            mLastMotionX = x;
            if (!scroller.isFinished()) {
                scroller.abortAnimation();
            }

            moving = false;
            // Log.i("TAG","ACTION_DOWN");

            return true;

        case MotionEvent.ACTION_MOVE:
            final int deltaX = (int) (mLastMotionX - x);
            boolean xMoved = Math.abs(deltaX) > 4;
            if (!moving && !xMoved)
                break;
            mLastMotionX = x;

            if ((0 == currentScreenIndex && deltaX < 0)
                    || (getChildCount() - 1 == currentScreenIndex && deltaX > 0))
                scrollBy(deltaX / 4, 0);
            else
                scrollBy(deltaX, 0);

            moving = true;

            {
                final int screenWidth = getWidth();
                currentScreenIndex = (getScrollX() + (screenWidth / 2))
                        / screenWidth;
            }

            return true;
        case MotionEvent.ACTION_UP:
            snapToDestination();

            if (!autoScroll) {
                startScroll();
            }
            if (!moving && null != onItemClickListener) {
                final int screenWidth = getWidth();
                int index = (int) ((getScrollX() + x) / screenWidth);
                onItemClickListener.onClick(index, getChildAt(index));
            }

            break;
        case MotionEvent.ACTION_CANCEL:
            snapToDestination();
            if (!autoScroll) {
                startScroll();
            }

        }
        return false;
    }

    private void scrollToScreen(int whichScreen) {
        // if (!scroller.isFinished())
        // return;
        // Log.e("TAG","scrollToScreen:"+whichScreen);
        if (whichScreen >= getChildCount())
            whichScreen = getChildCount() - 1;

        int delta = 0;

        delta = whichScreen * getWidth() - getScrollX();

        // scroller.startScroll(getScrollX(), 0, delta, 0, Math.abs(delta) * 2);
        scroller.startScroll(getScrollX(), 0, delta, 0, 1500);
        invalidate();

        currentScreenIndex = whichScreen;
    }

    private void snapToDestination() {
        final int x = getScrollX();
        final int screenWidth = getWidth();

        scrollToScreen((x + (screenWidth / 2)) / screenWidth);
    }

    public int getCurrentScreenIndex() {
        return currentScreenIndex;
    }

    public void startScroll() {

        autoScroll = true;
        handler.sendEmptyMessageDelayed(currentWhat, scrollTime);
    }

    public boolean isScrolling() {
        return autoScroll;
    }

    public void stopScroll() {
        autoScroll = false;
        currentWhat++;
    }

    @Override
    protected void finalize() throws Throwable {

        Log.e("TAG", "finalize===");

        super.finalize();
    }

    public OnItemClickListener getOnItemClickListener() {
        return onItemClickListener;
    }

    public void setOnItemClickListener(OnItemClickListener onItemClickListener) {
        this.onItemClickListener = onItemClickListener;
    }

    public interface OnItemClickListener {
        public void onClick(int index, View childview);
    }
    // OnClickListener onclick;
}
第二步：

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:orientation="vertical" >

<com.example.example.BannerLayout
android:id="@+id/layout_banner"
android:layout_width="match_parent"
android:layout_height="wrap_content" >


<ImageView
android:layout_width="fill_parent"
android:layout_height="wrap_content"
android:adjustViewBounds="true"
android:src="@drawable/gsydgsdfasdqwf" />

<ImageView
android:layout_width="fill_parent"
android:layout_height="wrap_content"
android:adjustViewBounds="true"
android:src="@drawable/hsfttyodfsd" />

<ImageView
android:layout_width="fill_parent"
android:layout_height="wrap_content"
android:adjustViewBounds="true"
android:src="@drawable/tsdssbd" />

<ImageView
android:layout_width="fill_parent"
android:layout_height="wrap_content"
android:adjustViewBounds="true"
android:src="@drawable/sdfdsf" />
</com.example.example.BannerLayout>

</LinearLayout>

第三步：

package com.example.example;

import android.os.Bundle;
import android.app.Activity;

public class MainActivity extends Activity {
    private BannerLayout banner;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        banner = (BannerLayout) findViewById(R.id.layout_banner);
    }

    @Override
    protected void onPause() {
        banner.stopScroll();
        super.onPause();
    }

    @Override
    protected void onRestart() {
        if (!banner.isScrolling())
            banner.startScroll();
        super.onRestart();
    }

    @Override
    protected void onResume() {
        if (!banner.isScrolling())
            banner.startScroll();
        super.onResume();
    }

    @Override
    protected void onStop() {
        banner.stopScroll();
        super.onStop();
    }

    @Override
    protected void onDestroy() {
        banner.stopScroll();
        super.onDestroy();
    }
}