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>
