团队项目——和谐共生（7）

距离上次发博客的时间有些久了，这次要实现的功能是Android调用系统相册

要实现这一功能，首先加入权限

<uses-permission android:name="android.permission.INTERNET" />
    <uses-permission android:name="android.permission.ACCESS_NETWORK_STATE" />
    <uses-permission android:name="android.permission.WRITE_EXTERNAL_STORAGE" />
    <uses-permission android:name="android.permission.CAMERA" />

然后是编写界面

<?xml version="1.0" encoding="utf-8"?>
<androidx.constraintlayout.widget.ConstraintLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:app="http://schemas.android.com/apk/res-auto"
    xmlns:tools="http://schemas.android.com/tools"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    tools:context=".MainActivity">

    <Button
        android:id="@+id/choose_photo"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:layout_marginTop="10dp"
        android:text="从相册中选择照片"
        android:textSize="20sp"
        app:layout_constraintTop_toTopOf="parent" />

    <ImageView
        android:id="@+id/picture"
        android:layout_width="0dp"
        android:layout_height="wrap_content"
        android:src="@drawable/shuishan"
        app:layout_constraintBottom_toBottomOf="parent"
        app:layout_constraintEnd_toEndOf="parent"
        app:layout_constraintStart_toStartOf="parent"
        app:layout_constraintTop_toTopOf="parent" />

</androidx.constraintlayout.widget.ConstraintLayout>

最后是后台代码

package com.example.pictureselect;

import androidx.annotation.NonNull;
import androidx.annotation.Nullable;
import androidx.annotation.RequiresApi;
import androidx.appcompat.app.AppCompatActivity;
import androidx.core.app.ActivityCompat;
import androidx.core.content.ContextCompat;

import android.Manifest;
import android.annotation.SuppressLint;
import android.content.ContentUris;
import android.content.Intent;
import android.content.SharedPreferences;
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.provider.DocumentsContract;
import android.provider.MediaStore;
import android.view.View;
import android.widget.Button;
import android.widget.ImageView;
import android.widget.Toast;

public class MainActivity extends AppCompatActivity {
    public static final int CHOOSE_PHOTO = 2;
    ImageView picture;
    String imagePath = null;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        Button btnChoosePhoto = (Button) findViewById(R.id.choose_photo);
        picture = (ImageView) findViewById(R.id.picture);
        btnChoosePhoto.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                requestPermissino();
            }
        });
        picture.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                requestPermissino();
            }
        });
    }

    private void requestPermissino() {
        if (ContextCompat.checkSelfPermission(this, Manifest.permission.WRITE_EXTERNAL_STORAGE) != PackageManager.PERMISSION_GRANTED) {
            ActivityCompat.requestPermissions(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); //打开相册
    }

    @Override
    public void onRequestPermissionsResult(int requestCode, @NonNull String[] permissions, @NonNull int[] grantResults) {
        super.onRequestPermissionsResult(requestCode, permissions, grantResults);
        switch (requestCode){
            case 1:
                if (grantResults.length>0 && grantResults[0] == PackageManager.PERMISSION_GRANTED){
                    openAlbum();
                }else {
                    Toast.makeText(this,"你拒绝了该权限",Toast.LENGTH_SHORT).show();
                }
                break;
            default:
                break;
        }
    }

    @Override
    protected void onActivityResult(int requestCode, int resultCode, @Nullable Intent data) {
        super.onActivityResult(requestCode, resultCode, data);
        switch (requestCode){
            case CHOOSE_PHOTO:
                if(resultCode == RESULT_OK){
                    //判断手机系统版本号
                    if(Build.VERSION.SDK_INT>=19){
                        //4.4及以上系统使用这个方法处理图片
                        handleImageOnKitKat(data);
                    }
                }
                break;
            default:
                break;
        }
    }

    @RequiresApi(api = Build.VERSION_CODES.KITKAT)
    private void handleImageOnKitKat(Intent data){
        Uri uri = data.getData();
        if(DocumentsContract.isDocumentUri(this,uri)){
            //如果是document类型的Uri，则通过document id处理
            String docId = DocumentsContract.getDocumentId(uri);
            if("com.android.providers.media.documents".equals(uri.getAuthority())){
                String id = docId.split(":")[1];  //解析出数字格式的id
                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())){
            //如果是file类型的Uri，直接获取图片路径即可
            imagePath = getImagePath(uri,null);
        }else if("file".equalsIgnoreCase(uri.getScheme())){
            //如果是file类型的Uri，直接获取图片路径即可
            imagePath = uri.getPath();
        }
        displayImage(imagePath); //根据图片路径显示图片
    }

    //将选择的图片Uri转换为路径
    @SuppressLint("Range")
    private String getImagePath(Uri uri, String selection){
        String path = null;
        //通过Uri和selection来获取真实的图片路径
        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;
    }

    //展示图片
    private void displayImage(String imagePath){
        if(imagePath!=null && !imagePath.equals("")){
            Bitmap bitmap = BitmapFactory.decodeFile(imagePath);
            picture.setImageBitmap(bitmap);
            //存储上次选择的图片路径，用以再次打开app设置图片
            SharedPreferences sp = getSharedPreferences("sp_img",MODE_PRIVATE);  //创建xml文件存储数据，name:创建的xml文件名
            SharedPreferences.Editor editor = sp.edit(); //获取edit()
            editor.putString("imgPath",imagePath);
            editor.apply();
        }else {
            Toast.makeText(this,"获取图片失败",Toast.LENGTH_SHORT).show();
        }
    }

    @Override
    protected void onResume() {
        super.onResume();
        //设置再次app时显示的图片
        SharedPreferences sp = getSharedPreferences("sp_img", MODE_PRIVATE);
        //取出上次存储的图片路径设置此次的图片展示
        String beforeImagePath = sp.getString("imgPath", null);
        displayImage(beforeImagePath);
    }
}

到此为止，这个功能就实现了，但不足的是他一次只能获取一张图片，之后会再进行优化。