ViewPager實現應用的歡迎界面

在前一篇博客中介紹了Animation實現應用的歡迎界面，本篇博客介紹ViewPager實現應用的歡迎引導界面，並且實現繼續向左滑動最後一張圖片進入新的Activity的效果。

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實現效果：

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項目結構：

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1.在activity_main.xml中添加ViewPager控件

<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"
    tools:context="${relativePackage}.${activityClass}" >

    <android.support.v4.view.ViewPager
        android:id="@+id/id_viewpager"
        android:layout_width="match_parent"
        android:layout_height="match_parent" >
    </android.support.v4.view.ViewPager>

</RelativeLayout>

2.添加要顯示的三張歡迎圖片到drawable文件夾中

3.MainActivity

package com.example.viewpager1;

import java.util.ArrayList;
import java.util.List;

import android.app.Activity;
import android.content.Intent;
import android.os.Bundle;
import android.support.v4.view.PagerAdapter;
import android.support.v4.view.ViewPager;
import android.support.v4.view.ViewPager.OnPageChangeListener;
import android.view.View;
import android.view.ViewGroup;
import android.view.Window;
import android.widget.ImageView;
import android.widget.ImageView.ScaleType;

public class MainActivity extends Activity {

    // 聲明ViewPager控件
    private ViewPager mViewPager;

    // 聲明圖片的id
    private int[] mImgIds = new int[] { R.drawable.a, R.drawable.b,
            R.drawable.c };

    // 定義存儲ImageView的集合
    private List<ImageView> mImages = new ArrayList<ImageView>();

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        // 去除標題
        requestWindowFeature(Window.FEATURE_NO_TITLE);

        setContentView(R.layout.activity_main);

        // 初始化ViewPager
        mViewPager = (ViewPager) findViewById(R.id.id_viewpager);
        // ========================爲ViewPager添加切換動畫效果開始========================
        // 動畫效果1 - DepthPageTransformer
        // mViewPager.setPageTransformer(true, new DepthPageTransformer());
        // 動畫效果2 - ZoomOutPageTransformer
        mViewPager.setPageTransformer(true, new ZoomOutPageTransformer());
        // ========================爲ViewPager添加切換動畫效果結束========================

        // 設置適配器
        mViewPager.setAdapter(new PagerAdapter() {

            @Override
            public Object instantiateItem(ViewGroup container, int position) {
                ImageView imageView = new ImageView(MainActivity.this);
                // 設置圖片
                imageView.setImageResource(mImgIds[position]);
                imageView.setScaleType(ScaleType.CENTER_CROP);
                container.addView(imageView);
                mImages.add(imageView);
                return imageView;
            }

            @Override
            public void destroyItem(ViewGroup container, int position,
                    Object object) {
                container.removeView(mImages.get(position));
            }

            @Override
            public boolean isViewFromObject(View view, Object object) {
                // TODO Auto-generated method stub
                return view == object;
            }

            @Override
            public int getCount() {
                // TODO Auto-generated method stub
                return mImgIds.length;
            }

        });

        // 綁定事件
        mViewPager.setOnPageChangeListener(new OnPageChangeListener() {

            @Override
            public void onPageSelected(int arg0) {
                // TODO Auto-generated method stub

            }

            @Override
            public void onPageScrolled(int arg0, float arg1, int arg2) {
                // 當滑動到最後一張圖片打開新的activity
                if (arg0 == mImgIds.length - 1) {
                    Intent intent = new Intent(MainActivity.this,
                            SecondActivity.class);
                    startActivity(intent);
                    finish();
                }
            }

            @Override
            public void onPageScrollStateChanged(int arg0) {
                // TODO Auto-generated method stub

            }
        });

    }
}

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官方API: http://developer.android.com/training/animation/screen-slide.html

提供了兩種ViewPager的切換動畫

DepthPageTransformer.java

package com.example.viewpager1;

import android.annotation.SuppressLint;
import android.support.v4.view.ViewPager;
import android.view.View;

@SuppressLint("NewApi")
public class DepthPageTransformer implements ViewPager.PageTransformer {
    private static final float MIN_SCALE = 0.75f;

    @SuppressLint("NewApi")
    public void transformPage(View view, float position) {
        int pageWidth = view.getWidth();

        if (position < -1) { // [-Infinity,-1)
            // This page is way off-screen to the left.
            view.setAlpha(0);

        } else if (position <= 0) { // [-1,0]
            // Use the default slide transition when moving to the left page
            view.setAlpha(1);
            view.setTranslationX(0);
            view.setScaleX(1);
            view.setScaleY(1);

        } else if (position <= 1) { // (0,1]
            // Fade the page out.
            view.setAlpha(1 - position);

            // Counteract the default slide transition
            view.setTranslationX(pageWidth * -position);

            // Scale the page down (between MIN_SCALE and 1)
            float scaleFactor = MIN_SCALE + (1 - MIN_SCALE)
                    * (1 - Math.abs(position));
            view.setScaleX(scaleFactor);
            view.setScaleY(scaleFactor);

        } else { // (1,+Infinity]
            // This page is way off-screen to the right.
            view.setAlpha(0);
        }
    }
}

ZoomOutPageTransformer.java

package com.example.viewpager1;

import android.annotation.SuppressLint;
import android.support.v4.view.ViewPager;
import android.view.View;

@SuppressLint("NewApi")
public class ZoomOutPageTransformer implements ViewPager.PageTransformer {
    private static final float MIN_SCALE = 0.85f;
    private static final float MIN_ALPHA = 0.5f;

    @SuppressLint("NewApi")
    public void transformPage(View view, float position) {
        int pageWidth = view.getWidth();
        int pageHeight = view.getHeight();

        if (position < -1) { // [-Infinity,-1)
            // This page is way off-screen to the left.
            view.setAlpha(0);

        } else if (position <= 1) { // [-1,1]
            // Modify the default slide transition to shrink the page as well
            float scaleFactor = Math.max(MIN_SCALE, 1 - Math.abs(position));
            float vertMargin = pageHeight * (1 - scaleFactor) / 2;
            float horzMargin = pageWidth * (1 - scaleFactor) / 2;
            if (position < 0) {
                view.setTranslationX(horzMargin - vertMargin / 2);
            } else {
                view.setTranslationX(-horzMargin + vertMargin / 2);
            }

            // Scale the page down (between MIN_SCALE and 1)
            view.setScaleX(scaleFactor);
            view.setScaleY(scaleFactor);

            // Fade the page relative to its size.
            view.setAlpha(MIN_ALPHA + (scaleFactor - MIN_SCALE)
                    / (1 - MIN_SCALE) * (1 - MIN_ALPHA));

        } else { // (1,+Infinity]
            // This page is way off-screen to the right.
            view.setAlpha(0);
        }
    }
}