内容提供者-获取媒体库里的图片

对于媒体内容提供者的应用场景有哪些呢？

比如说你的上传头像，比如说你做行车记录的，抓拍图片功能用户查看预览，比如说你的微信,QQ发动态，比如说你淘宝购物，要从图片中扫描二维码。这些都从图库里拿这个图片。

在android中有一个提供者中做MediaProvider

源码地址：

MediaProvider

获取到图片内容

URI

uri这些我们就不详细去看了，可以从源码中得知道

另外则是这些URI有常量：

• 图片的Url

MediaStore.Images.Media.EXTERNAL_CONTENT_URI

• 视频的Url

MediaStore.Video.Media.EXTERNAL_CONTENT_URI

• 音频的

MediaStore.Audio.Media.EXTERNAL_CONTENT_URI

权限

    <uses-permission android:name="android.permission.READ_EXTERNAL_STORAGE" />

检查权限

    private void checkPermission() {
        int readExternalStoragePermissionResult = checkSelfPermission(Manifest.permission.READ_EXTERNAL_STORAGE);
        if(readExternalStoragePermissionResult != PackageManager.PERMISSION_GRANTED) {
            requestPermissions(new String[]{Manifest.permission.READ_EXTERNAL_STORAGE},PERMISSION_REQUEST_CODE);
        }
    }

权限结果，如果没有权限就没法进行

数据表字段

用以前的方法我们就可以获得表的内容和字段

 ContentResolver contentResolver = getContentResolver();
        Uri uri = MediaStore.Images.Media.EXTERNAL_CONTENT_URI;
        Cursor query = contentResolver.query(uri,null,null,null,null,null);
        String[] columnNames = query.getColumnNames();
        while(query.moveToNext()) {
            Log.d(TAG,"----------------------------");
            for(String columnName : columnNames) {
                Log.d(TAG,columnName + " ==== " + query.getString(query.getColumnIndex(columnName)));
            }
            Log.d(TAG,"----------------------------");
        }
        query.close();

那我们就知道需要什么字段了吧

• 路径_data
• 图片名称_display_name
• 时间date_added

还有经纬度什么的，对吧！通过这个经纬度+API转换就可以得到地址了，所以图片里可能包含着地理信息哦。

准备一个封装数据的bean类

public class PhotoItem {

    private String path;
    private String name;
    private long createDate;
    private boolean isSelected = false;


    public boolean isSelected() {
        return isSelected;
    }

    public void setSelected(boolean selected) {
        isSelected = selected;
    }

    public String getPath() {
        return path;
    }

    public void setPath(String path) {
        this.path = path;
    }

    public String getName() {
        return name;
    }

    public void setName(String name) {
        this.name = name;
    }

    public long getCreateDate() {
        return createDate;
    }

    public void setCreateDate(long createDate) {
        this.createDate = createDate;
    }
}

下面我们就获取到图片的数据，并且封装起来，显示出来

package com.sunofbeaches.imagepickerdemo;

import android.content.ContentResolver;
import android.database.Cursor;
import android.net.Uri;
import android.os.Bundle;
import android.provider.MediaStore;

import com.sunofbeaches.imagepickerdemo.domain.PhotoItem;

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

import androidx.annotation.Nullable;
import androidx.appcompat.app.AppCompatActivity;
import androidx.recyclerview.widget.GridLayoutManager;
import androidx.recyclerview.widget.RecyclerView;


public class ImagePickerActivity extends AppCompatActivity {

    private static final String TAG = "ImagePickerActivity";
    private RecyclerView mPicListView;
    private List<PhotoItem> mPics = new ArrayList<>();
    private PicListAdapter mPicListAdapter;

    @Override
    protected void onCreate(@Nullable Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_image_picker);
        initView();
        initData();
    }

    private void initData() {
        //这些事情其实不能在主线程做，我们稍后修改
        ContentResolver contentResolver = getContentResolver();
        Uri uri = MediaStore.Images.Media.EXTERNAL_CONTENT_URI;
        Cursor query = contentResolver.query(uri,new String[]{
                MediaStore.Images.Media.DATA,
                MediaStore.Images.Media.DISPLAY_NAME,
                MediaStore.Images.Media.DATE_ADDED,
                MediaStore.Images.Media._ID},null,null,null,null);
        while(query.moveToNext()) {
            PhotoItem photoItem = new PhotoItem();
            photoItem.setPath(query.getString(0));
            //这里的下标跟上面的query第一个参数对应，时间是第2个，所以下标为1
            photoItem.setCreateDate(query.getLong(1));
            photoItem.setName(query.getString(2));
            mPics.add(photoItem);
        }
        query.close();
        mPicListAdapter.setData(mPics);
    }


    private void initView() {
        mPicListView = this.findViewById(R.id.pic_list);
        mPicListView.setLayoutManager(new GridLayoutManager(this,3));
        mPicListAdapter = new PicListAdapter();
        mPicListView.setAdapter(mPicListAdapter);
    }


}

适配器代码：

public class PicListAdapter extends RecyclerView.Adapter<PicListAdapter.InnerHolder> {

    private List<PhotoItem> mData = new ArrayList<>();

    @NonNull
    @Override
    public InnerHolder onCreateViewHolder(@NonNull ViewGroup parent,int viewType) {
        ImageView iv = new ImageView(parent.getContext());
        iv.setScaleType(ImageView.ScaleType.CENTER_CROP);
        Point point = new Point();
        ((WindowManager) parent.getContext().getSystemService(Context.WINDOW_SERVICE)).getDefaultDisplay().getSize(point);
        RecyclerView.LayoutParams layoutParams = new RecyclerView.LayoutParams(point.x / 3,point.x / 3);
        iv.setLayoutParams(layoutParams);
        return new InnerHolder(iv);
    }

    @Override
    public void onBindViewHolder(@NonNull InnerHolder holder,int position) {
        if(holder.itemView instanceof ImageView) {
            Glide.with(holder.itemView.getContext()).load(mData.get(position).getPath()).into((ImageView) holder.itemView);
        }
    }

    @Override
    public int getItemCount() {
        return mData.size();
    }

    public void setData(List<PhotoItem> pics) {
        mData.clear();
        mData.addAll(pics);
        notifyDataSetChanged();
    }

    public class InnerHolder extends RecyclerView.ViewHolder {
        public InnerHolder(@NonNull View itemView) {
            super(itemView);
        }
    }
}

运行结果

用LoaderManager来加载

前面我们直接在onCreate的地方加载数据，如果数据量大的话，会导致主线程阻塞出现ANR异常。如果数据量小，会影响页面的打开速度。

所以我们要么自己创建子线程去获取，或者可以通过LoaderManager去获取。

public class MediaContentPickerActivity extends AppCompatActivity {

    private static final int LOADER_ALL = 0;         // 获取所有图片
    private static final String TAG = "ContentPickerActivity";
    private List<PhotoItem> photoInfoList = new ArrayList<>();      // 本地图片信息List


    @Override
    protected void onCreate(@Nullable Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_media_picker);
        initLoader();
    }

    private void initLoader() {
        LoaderManager loaderManager = LoaderManager.getInstance(this);
        loaderManager.initLoader(LOADER_ALL,null,new LoaderManager.LoaderCallbacks<Cursor>() {
            private final String[] IMAGE_PROJECTION = {
                    MediaStore.Images.Media.DATA,
                    MediaStore.Images.Media.DISPLAY_NAME,
                    MediaStore.Images.Media.DATE_ADDED,
                    MediaStore.Images.Media._ID,
            };

            @NonNull
            @Override
            public Loader<Cursor> onCreateLoader(int id,@Nullable Bundle args) {
                if(id == LOADER_ALL) {
                    return new CursorLoader(MediaContentPickerActivity.this,
                            MediaStore.Images.Media.EXTERNAL_CONTENT_URI,IMAGE_PROJECTION,
                            null,null,IMAGE_PROJECTION[2] + " DESC");
                }
                return null;
            }

            @Override
            public void onLoadFinished(@NonNull Loader<Cursor> loader,Cursor data) {
                if(data != null) {
                    int count = data.getCount();
                    if(count > 0) {
                        List<PhotoItem> tempPhotoList = new ArrayList<>();
                        data.moveToFirst();
                        do {
                            String path = data.getString(data.getColumnIndexOrThrow(IMAGE_PROJECTION[0]));
                            String name = data.getString(data.getColumnIndexOrThrow(IMAGE_PROJECTION[1]));
                            long dateTime = data.getLong(data.getColumnIndexOrThrow(IMAGE_PROJECTION[2]));
                            PhotoItem photoItem = new PhotoItem();
                            photoItem.setName(name);
                            photoItem.setPath(path);
                            photoItem.setCreateDate(dateTime);
                            tempPhotoList.add(photoItem);
                        } while(data.moveToNext());
                        photoInfoList.clear();
                        photoInfoList.addAll(tempPhotoList);
                    }
                    //输出结果
                    for(PhotoItem photoItem : photoInfoList) {
                        Log.d(TAG,"photoItem -- > " + photoItem);
                    }
                }
            }

            @Override
            public void onLoaderReset(@NonNull Loader<Cursor> loader) {

            }
        });
    }

}

给PhotoItem.java添加toString方法

    @Override
    public String toString() {
        return "PhotoItem{" +
                "path='" + path + '\'' +
                ", name='" + name + '\'' +
                ", createDate=" + createDate +
                ", isSelected=" + isSelected +
                '}';
    }

获取结果

okay啦，到这里我们就把图片获取出来了，到了我们的网络课程，我们会模拟一个发朋友圈的功能，我们就会用到这些图片了。

相关图片资料

图片素材，右键另存为即可