名词解析

MediaStore：图像（包括音频和视频）的标准内容提供者。它在设备上存放文件的设置，并为存储了和检索该文件的元数据提供便利。
元数据是对数据的描述，包括数据本身的信息如大小、名称，以及附加的其他数据如标题、描叙、经度、纬度等。
EXIF表示可交换的图像文件格式（Exchangeable Image File Format）,它是在图像文件中保存元数据的一种标准方式。

代码实现

下面的代码实现了：通过查询MediaStore获取图片，并以幻灯片的形式自动播放，点击图片暂停或继续
MainActivity.java

import android.database.Cursor;
import android.graphics.Bitmap;
import android.graphics.BitmapFactory;
import android.graphics.Matrix;
import android.media.ExifInterface;
import android.os.Bundle;
import android.os.Handler;
import android.os.Message;
import android.provider.MediaStore;
import android.provider.MediaStore.Images.Media;
import android.support.v4.content.CursorLoader;
import android.support.v7.app.AppCompatActivity;
import android.util.Log;
import android.view.View;
import android.widget.ImageButton;
import android.widget.TextView;

import java.io.IOException;
import java.util.Timer;
import java.util.TimerTask;

public class MainActivity extends AppCompatActivity {

    public static final int DISPLAY_WIDTH = 400;
    public static final int DISPLAY_HEIGHT = 400;

    TextView titleTextView;
    TextView displayTextView;
    ImageButton mImageButton;
    Cursor cursor;
    Bitmap bmp;
    String imageFilePath;
    int fileColumn;
    int titleColumn;
    int displayColumn;

    Timer timer;
    boolean isPause = true;


    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);

        titleTextView = (TextView) findViewById(R.id.tv_title);
        displayTextView = (TextView) findViewById(R.id.tv_display);
        mImageButton = (ImageButton) findViewById(R.id.image);

        String[] columns = {MediaStore.Images.Media.DATA,
                Media._ID,
                Media.TITLE,
                Media.DISPLAY_NAME};
        cursor = new CursorLoader(this, Media.EXTERNAL_CONTENT_URI,columns,null,null,null)
                .loadInBackground();

        fileColumn = cursor.getColumnIndexOrThrow(Media.DATA);
        titleColumn = cursor.getColumnIndexOrThrow(Media.TITLE);
        displayColumn = cursor.getColumnIndexOrThrow(Media.DISPLAY_NAME);

        //显示第一张图片
        if(cursor.moveToFirst()){
            titleTextView.setText(cursor.getString(titleColumn));
            displayTextView.setText(cursor.getString(displayColumn));
            imageFilePath = cursor.getString(fileColumn);
            bmp = getbitMap(imageFilePath);
            mImageButton.setImageBitmap(bmp);
        }

        final Handler handler = new Handler(){
            @Override
            public void handleMessage(Message msg) {
                if(cursor.moveToNext()){
                    titleTextView.setText(cursor.getString(titleColumn));
                    displayTextView.setText(cursor.getString(displayColumn));
                    imageFilePath = cursor.getString(fileColumn);
                    bmp = getbitMap(imageFilePath);
                    mImageButton.setImageBitmap(bmp);
                }
            }
        };

        timer = new Timer();

        //点击暂停或继续播放
        mImageButton.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                isPause = !isPause;
                if(isPause){
                    timer.cancel();
                }else{
                    timer = new Timer();
                    timer.scheduleAtFixedRate(new TimerTask() {
                        @Override
                        public void run() {
                            handler.sendEmptyMessage(0);
                        }
                    },0,1000);
                }
            }
        });
    }


    private Bitmap getbitMap(String imageFilePath) {

        //加载图像的尺寸而不是图像本身
        BitmapFactory.Options options = new BitmapFactory.Options();
        options.inJustDecodeBounds = true;
        Bitmap bitmap = BitmapFactory.decodeFile(imageFilePath,options);
        int widthRatio = (int) Math.ceil(options.outWidth/(float)DISPLAY_WIDTH);
        int heightRatio = (int) Math.ceil(options.outHeight/(float)DISPLAY_HEIGHT);

        Log.v("HEIGHTRATIO",""+heightRatio);
        Log.v("WIDTHRATIO",""+widthRatio);

        //如果两个比例都大于1，那么图像的一条边将大于屏幕
        if(heightRatio > 1 && widthRatio > 1){
            options.inSampleSize = Math.max(heightRatio,widthRatio);
        }

        //对它进行真正的解码
        options.inJustDecodeBounds = false; // 此处为false，不只是解码
        bitmap = BitmapFactory.decodeFile(imageFilePath,options);
        //修复图片方向
        Matrix m = repairBitmapDirection(imageFilePath);
        if(m != null){
            bitmap = Bitmap.createBitmap(bitmap, 0, 0, bitmap.getWidth(),
                    bitmap.getHeight(), m, true);
        }

        return bitmap;
    }

    /**
     * 识别图片方向
     * @param filepath
     * @return
     */
    private Matrix repairBitmapDirection(String filepath) {
        //根据图片的filepath获取到一个ExifInterface的对象
        ExifInterface exif = null;
        try {
            exif = new ExifInterface(filepath);
        } catch (IOException e) {
            e.printStackTrace();
            exif = null;
        }

        int degree = 0;
        if (exif != null) {
            // 读取图片中相机方向信息
            int ori = exif.getAttributeInt(ExifInterface.TAG_ORIENTATION,
                    ExifInterface.ORIENTATION_UNDEFINED);
            // 计算旋转角度
            switch (ori) {
                case ExifInterface.ORIENTATION_ROTATE_90:
                    degree = 90;
                    break;
                case ExifInterface.ORIENTATION_ROTATE_180:
                    degree = 180;
                    break;
                case ExifInterface.ORIENTATION_ROTATE_270:
                    degree = 270;
                    break;
                default:
                    degree = 0;
                    break;
            }

        }
        if (degree != 0) {
            // 旋转图片
            Matrix m = new Matrix();
            m.postRotate(degree);
            return m;
        }
        return null;
    }

}

activity_main.xml

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout
    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:paddingBottom="@dimen/activity_vertical_margin"
    android:paddingLeft="@dimen/activity_horizontal_margin"
    android:paddingRight="@dimen/activity_horizontal_margin"
    android:paddingTop="@dimen/activity_vertical_margin"
    android:orientation="vertical"
    tools:context="com.xwe.mediademo.MainActivity">

    <ImageButton
        android:id="@+id/image"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"/>

    <TextView
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:id="@+id/tv_title"/>
    <TextView
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:id="@+id/tv_display"/>
</LinearLayout>