Android---打开相册选择图片

简单实现打开系统相册选择一张图片并显示在UI上，适用与个人主页头像的切换。

1. 添加存储权限。AndroidManifest.xml里添加读取内存的权限。

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

2. 布局。布局内容比较交单，一个Button用来打开相册；一个ImageView用来接收从相册选择的图片。

<?xml version="1.0" encoding="utf-8"?>
<RelativeLayout 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"
    tools:context=".MainActivity">

    <Button
        android:id="@+id/btn_open_gallery"
        android:layout_width="150dp"
        android:layout_height="75dp"
        android:layout_centerHorizontal="true"
        android:text="打开相册"
        android:textSize="20sp"/>
    
    <ImageView
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_centerHorizontal="true"
        android:layout_marginTop="10dp"
        android:layout_below="@+id/btn_open_gallery"/>
    
</RelativeLayout>

3. 动态申请权限。Google 在 Android 6.0 开始引入了权限申请机制，除了再AndroidManifest.xml里申请静态权限，还需要在代码里动态申请。

/**
* 申请动态权限
*/
private void applyPermission() {
    //检测权限
    if (ContextCompat.checkSelfPermission(this, Manifest.permission.WRITE_EXTERNAL_STORAGE)
                != PackageManager.PERMISSION_GRANTED) {
            // 如果没有权限，则申请需要的权限
        ActivityCompat.requestPermissions(this,
                    new String[]{Manifest.permission.READ_EXTERNAL_STORAGE}, PERMISSION_REQUEST_CODE);
    }else {
        // 已经申请了权限
        openGallery();
    }
}

4. 申请权限的回调。

    /**
     * 用户选择是否开启权限操作后的回调；TODO 同意/拒绝
     */
    @Override
    public void onRequestPermissionsResult(int requestCode, @NonNull String[] permissions, @NonNull int[] grantResults) {
        super.onRequestPermissionsResult(requestCode, permissions, grantResults);
        if (requestCode == PERMISSION_REQUEST_CODE) {
            if (grantResults.length > 0 && grantResults[0] == PackageManager.PERMISSION_GRANTED) {
                // 用户同样授权
                openGallery();
            }else {
                // 用户拒绝授权
                Toast.makeText(this, "你拒绝使用存储权限！", Toast.LENGTH_SHORT).show();
                Log.d("HL", "你拒绝使用存储权限！");
            }
        }
    }

5. 打开相册。

    /**
     * 打开相册
     */
    private void openGallery() {
        Intent intent = new Intent(Intent.ACTION_PICK, null);
        intent.setDataAndType(MediaStore.Images.Media.EXTERNAL_CONTENT_URI , "image/*");
        startActivityForResult(intent, OPEN_GALLERY_REQUEST_CODE);
    }

6. 结果回调。用户选择了一张图片，接收返回的结果并在ImageView里显示。、

    @Override
    protected void onActivityResult(int requestCode, int resultCode, @Nullable Intent data) {
        super.onActivityResult(requestCode, resultCode, data);
        if (requestCode == OPEN_GALLERY_REQUEST_CODE) { // 检测请求码
            if (resultCode == Activity.RESULT_OK && data != null) {
                try {
                    InputStream inputStream = getContentResolver().openInputStream(data.getData());
                    Bitmap bitmap = BitmapFactory.decodeStream(inputStream);
                    // TODO 把获取到的图片放到ImageView上
                    mImg.setImageBitmap(bitmap);
                } catch (FileNotFoundException e) {
                    e.printStackTrace();
                }
            }
        }
    }

完整Demo

package com.example.opengallery;

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

import android.Manifest;
import android.app.Activity;
import android.content.Intent;
import android.content.pm.PackageManager;
import android.graphics.Bitmap;
import android.graphics.BitmapFactory;
import android.os.Bundle;
import android.provider.MediaStore;
import android.util.Log;
import android.widget.Button;
import android.widget.ImageView;
import android.widget.Toast;

import java.io.FileNotFoundException;
import java.io.InputStream;

public class MainActivity extends AppCompatActivity {

    private static final int PERMISSION_REQUEST_CODE = 0;
    private static final int OPEN_GALLERY_REQUEST_CODE = 1;
    private static final int TAKE_PHOTO_REQUEST_CODE = 2;

    private Button mOpenGallery;
    private ImageView mImg;

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

        mOpenGallery = findViewById(R.id.btn_open_gallery);
        mImg = findViewById(R.id.img);

        //打开相册
        mOpenGallery.setOnClickListener(v -> {
            applyPermission();
        });

    }

    /**
     * 申请动态权限
     */
    private void applyPermission() {
        //检测权限
        if (ContextCompat.checkSelfPermission(this, Manifest.permission.WRITE_EXTERNAL_STORAGE)
                != PackageManager.PERMISSION_GRANTED) {
            // 如果没有权限，则申请需要的权限
            ActivityCompat.requestPermissions(this,
                    new String[]{Manifest.permission.READ_EXTERNAL_STORAGE}, PERMISSION_REQUEST_CODE);
        }else {
            // 已经申请了权限
            openGallery();
        }
    }

    /**
     * 用户选择是否开启权限操作后的回调；TODO 同意/拒绝
     */
    @Override
    public void onRequestPermissionsResult(int requestCode, @NonNull String[] permissions, @NonNull int[] grantResults) {
        super.onRequestPermissionsResult(requestCode, permissions, grantResults);
        if (requestCode == PERMISSION_REQUEST_CODE) {
            if (grantResults.length > 0 && grantResults[0] == PackageManager.PERMISSION_GRANTED) {
                // 用户同样授权
                openGallery();
            }else {
                // 用户拒绝授权
                Toast.makeText(this, "你拒绝使用存储权限！", Toast.LENGTH_SHORT).show();
                Log.d("HL", "你拒绝使用存储权限！");
            }
        }
    }

    /**
     * 打开相册
     */
    private void openGallery() {
        Intent intent = new Intent(Intent.ACTION_PICK, null);
        intent.setDataAndType(MediaStore.Images.Media.EXTERNAL_CONTENT_URI , "image/*");
        startActivityForResult(intent, OPEN_GALLERY_REQUEST_CODE);
    }

    @Override
    protected void onActivityResult(int requestCode, int resultCode, @Nullable Intent data) {
        super.onActivityResult(requestCode, resultCode, data);
        if (requestCode == OPEN_GALLERY_REQUEST_CODE) { // 检测请求码
            if (resultCode == Activity.RESULT_OK && data != null) {
                try {
                    InputStream inputStream = getContentResolver().openInputStream(data.getData());
                    Bitmap bitmap = BitmapFactory.decodeStream(inputStream);
                    // TODO 把获取到的图片放到ImageView上
                    mImg.setImageBitmap(bitmap);
                } catch (FileNotFoundException e) {
                    e.printStackTrace();
                }
            }
        }
    }
}