《第一行代码》读书笔记（七）：album爬坑

权限问题

尽管书中提到4.4系统之前需要声明访问SD卡权限，不过很遗憾，4.4系统之后仍然需要

照片不显示问题

Android10对文件访问权限进行了调整，原来的方法需要修改。

代码

综上，只需修改文件AndroidManifest.xml和MainActivity.java即可。

AndroidManifest.xml

<?xml version="1.0" encoding="utf-8"?>
<manifest xmlns:android="http://schemas.android.com/apk/res/android"
    package="com.example.cameraalbumtest">
    <uses-permission android:name="android.permission.WRITE_EXTERNAL_STORAGE"/>

    <application
        android:allowBackup="true"
        android:icon="@mipmap/ic_launcher"
        android:label="@string/app_name"
        android:roundIcon="@mipmap/ic_launcher_round"
        android:supportsRtl="true"
        android:theme="@style/AppTheme">
        <activity android:name=".MainActivity">
            <intent-filter>
                <action android:name="android.intent.action.MAIN" />

                <category android:name="android.intent.category.LAUNCHER" />
            </intent-filter>
        </activity>
        <provider
            android:authorities="com.example.cameraalbumtest.fileprovider"
            android:name="androidx.core.content.FileProvider"
            android:exported="false"
            android:grantUriPermissions="true">
            <meta-data
                android:name="android.support.FILE_PROVIDER_PATHS"
                android:resource="@xml/file_paths"/>
        </provider>
    </application>

</manifest>

MainActivity.java

详细的更改见注释。

package com.example.cameraalbumtest;

import androidx.appcompat.app.AppCompatActivity;
import androidx.core.app.ActivityCompat;
import androidx.core.content.ContextCompat;
import androidx.core.content.FileProvider;

import android.Manifest;
import android.annotation.TargetApi;
import android.content.ContentUris;
import android.content.ContentValues;
import android.content.Context;
import android.content.Intent;
import android.content.pm.PackageManager;
import android.database.Cursor;
import android.graphics.Bitmap;
import android.graphics.BitmapFactory;
import android.net.Uri;
import android.os.Build;
import android.os.Bundle;
import android.os.ParcelFileDescriptor;
import android.provider.DocumentsContract;
import android.provider.MediaStore;
import android.view.View;
import android.widget.Button;
import android.widget.ImageView;
import android.widget.Toast;

import java.io.File;
import java.io.FileDescriptor;

public class MainActivity extends AppCompatActivity {
    private static final int TAKE_PHOTO = 1;
    private ImageView picture;
    private Uri imageUri;

    public static final int CHOOSE_PHOTO = 2;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        Button takePhoto = (Button) findViewById(R.id.take_photo);
        Button chooseFromAlbum = (Button) findViewById(R.id.choose_from_album);
        picture = (ImageView) findViewById(R.id.picture);
        takePhoto.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                File outputImage = new File(getExternalCacheDir(),"output_image.jpg");
                try{
                    if(outputImage.exists()){
                        outputImage.delete();
                    }
                    outputImage.createNewFile();
                }catch (Exception e){
                    e.printStackTrace();
                }
                if(Build.VERSION.SDK_INT>=24){
                    imageUri = FileProvider.getUriForFile(MainActivity.this,"com.example.cameraalbumtest.fileprovider",outputImage);
                }else{
                    imageUri=Uri.fromFile(outputImage);
                }
                Intent intent = new Intent("android.media.action.IMAGE_CAPTURE");
                intent.putExtra(MediaStore.EXTRA_OUTPUT,imageUri);
                startActivityForResult(intent,TAKE_PHOTO);
            }
        });
        chooseFromAlbum.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                if(ContextCompat.checkSelfPermission(MainActivity.this, Manifest.permission.WRITE_EXTERNAL_STORAGE)!= PackageManager.PERMISSION_GRANTED){
                    ActivityCompat.requestPermissions(MainActivity.this,new String[] {Manifest.permission.WRITE_EXTERNAL_STORAGE},1);
                }else{
                    openAlbum();
                }
            }
        });
    }

    private void openAlbum(){
        Intent intent = new Intent("android.intent.action.GET_CONTENT");
        intent.setType("image/*");
        startActivityForResult(intent,CHOOSE_PHOTO);
    }

    @Override
    public void onRequestPermissionsResult(int requestCode,String[] permissions,int[] grantResults){
        switch(requestCode){
            case 1:
                if(grantResults.length>0&&grantResults[0]==PackageManager.PERMISSION_GRANTED){
                    openAlbum();
                }else{
                    Toast.makeText(this,"You denied the permission",Toast.LENGTH_SHORT).show();
                }
                break;
            default:
                break;
        }
    }
    @Override
    protected void onActivityResult(int requestCode,int resultCode,Intent data){
        super.onActivityResult(requestCode, resultCode, data);
        switch(requestCode){
            case TAKE_PHOTO:
                if(resultCode==RESULT_OK){
                    try{
                        Bitmap bitmap = BitmapFactory.decodeStream(getContentResolver().openInputStream(imageUri));
                        picture.setImageBitmap(bitmap);
                    }catch(Exception e){
                        e.printStackTrace();
                    }
                }
                break;
            case CHOOSE_PHOTO:
                if(resultCode==RESULT_OK){
                    if(Build.VERSION.SDK_INT>=19){
                        handleImageOnKitKat(data);
                    }else{
                        handleImageBeforeKitKat(data);
                    }
                }
                break;
            default:
                break;
        }
    }

    @TargetApi(19)
    private void handleImageOnKitKat(Intent data){
        String imagePath = null;
        Uri uri = data.getData();
        if(DocumentsContract.isDocumentUri(this,uri)){
            String docId = DocumentsContract.getDocumentId(uri);
            if("com.android.providers.media.documents".equals(uri.getAuthority())){
                String id = docId.split(":")[1];
                String selection = MediaStore.Images.Media._ID+"="+id;
                imagePath = getImagePath(MediaStore.Images.Media.EXTERNAL_CONTENT_URI,selection);
            }else if("com.android.providers.downloads.documents".equals(uri.getAuthority())){
                Uri contentUri = ContentUris.withAppendedId(Uri.parse("content://downloads/public_downloads"),Long.valueOf(docId));
                imagePath = getImagePath(contentUri,null);
            }
        }else if("content".equalsIgnoreCase(uri.getScheme())){
            imagePath = getImagePath(uri,null);
        }else if("file".equalsIgnoreCase(uri.getScheme())){
            imagePath = uri.getPath();
        }
        displayImage(imagePath);
    }

    private void handleImageBeforeKitKat(Intent data){
        Uri uri = data.getData();
        String imagePath = getImagePath(uri,null);
        displayImage(imagePath);
    }

    private String getImagePath(Uri uri,String selection){
        String path = null;
        Cursor cursor = getContentResolver().query(uri,null,selection,null,null);
        if(cursor!=null){
            if(cursor.moveToFirst()){
                path = cursor.getString(cursor.getColumnIndex(MediaStore.Images.Media.DATA));
            }
            cursor.close();
        }
        return path;
    }

    private void displayImage(String imagePath){
        if(imagePath!=null){
            Bitmap bitmap = getBitmapFromUri(this, getImageContentUri(this,imagePath));
            picture.setImageBitmap(bitmap);
        }else{
            Toast.makeText(this,"failed to get image",Toast.LENGTH_SHORT).show();
        }
    }
    public static Uri getImageContentUri(Context context, String path) {
        Cursor cursor = context.getContentResolver().query(MediaStore.Images.Media.EXTERNAL_CONTENT_URI,
                new String[] { MediaStore.Images.Media._ID }, MediaStore.Images.Media.DATA + "=? ",
                new String[] { path }, null);
        if (cursor != null && cursor.moveToFirst()) {
            int id = cursor.getInt(cursor.getColumnIndex(MediaStore.MediaColumns._ID));
            Uri baseUri = Uri.parse("content://media/external/images/media");
            return Uri.withAppendedPath(baseUri, "" + id);
        } else {
            // 如果图片不在手机的共享图片数据库，就先把它插入。
            if (new File(path).exists()) {
                ContentValues values = new ContentValues();
                values.put(MediaStore.Images.Media.DATA, path);
                return context.getContentResolver().insert(MediaStore.Images.Media.EXTERNAL_CONTENT_URI, values);
            } else {
                return null;
            }
        }
    }
    public static Bitmap getBitmapFromUri(Context context, Uri uri) {
        try {
            ParcelFileDescriptor parcelFileDescriptor =
                    context.getContentResolver().openFileDescriptor(uri, "r");
            FileDescriptor fileDescriptor = parcelFileDescriptor.getFileDescriptor();
            Bitmap image = BitmapFactory.decodeFileDescriptor(fileDescriptor);
            parcelFileDescriptor.close();
            return image;
        } catch (Exception e) {
            e.printStackTrace();
        }
        return null;
    }
}

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