3、Android基础知识-相册获取按钮&保存图片按钮

基本思想：在Android上添加从相册中取图片和将图片保存到相册中 参考nihui大佬代码（真心不会Android）

一、创建按钮同时并拖动到指定位置，这里使用得constraintLayout布局

（1）、拖拽按钮

（2）、然后修改按钮得名字和添加imageview界面

（3）、在Mainactivity函数中进行java代码调用编写

（4）、详细代码片段-1

imageView = (ImageView) findViewById(R.id.imageView);
Button buttonImage = (Button) findViewById(R.id.button);
buttonImage.setOnClickListener(new View.OnClickListener() {
@Override
 public void onClick(View arg0) {
        Intent i = new Intent(Intent.ACTION_PICK);
        i.setType("image/*");
        startActivityForResult(i, 1);
     }
});

代码片段-2

  @Override
    protected void onActivityResult(int requestCode, int resultCode, Intent data)
    {
        super.onActivityResult(requestCode, resultCode, data);

        if (resultCode == RESULT_OK && null != data) {
            Uri selectedImage = data.getData();

            try
            {
                switch (requestCode)
                {
                    case 1 :
                        bitmap = decodeUri(selectedImage);

                        yourSelectedImage = bitmap.copy(Bitmap.Config.ARGB_8888, true);

                        imageView.setImageBitmap(bitmap);
                        break;
                    default:
                        break;
                }
            }
            catch (FileNotFoundException e)
            {
                Log.e("MainActivity", "FileNotFoundException");
                return;
            }
        }
    }

    private Bitmap decodeUri(Uri selectedImage) throws FileNotFoundException
    {
        // Decode image size
        BitmapFactory.Options o = new BitmapFactory.Options();
        o.inJustDecodeBounds = true;
        BitmapFactory.decodeStream(getContentResolver().openInputStream(selectedImage), null, o);

        // The new size we want to scale to
        final int REQUIRED_SIZE = 640;

        // Find the correct scale value. It should be the power of 2.
        int width_tmp = o.outWidth, height_tmp = o.outHeight;
        int scale = 1;
        while (true) {
            if (width_tmp / 2 < REQUIRED_SIZE
                    || height_tmp / 2 < REQUIRED_SIZE) {
                break;
            }
            width_tmp /= 2;
            height_tmp /= 2;
            scale *= 2;
        }

        // Decode with inSampleSize
        BitmapFactory.Options o2 = new BitmapFactory.Options();
        o2.inSampleSize = scale;
        Bitmap bitmap = BitmapFactory.decodeStream(getContentResolver().openInputStream(selectedImage), null, o2);

        // Rotate according to EXIF
        int rotate = 0;
        try
        {
            ExifInterface exif = new ExifInterface(getContentResolver().openInputStream(selectedImage));
            int orientation = exif.getAttributeInt(ExifInterface.TAG_ORIENTATION, ExifInterface.ORIENTATION_NORMAL);
            switch (orientation) {
                case ExifInterface.ORIENTATION_ROTATE_270:
                    rotate = 270;
                    break;
                case ExifInterface.ORIENTATION_ROTATE_180:
                    rotate = 180;
                    break;
                case ExifInterface.ORIENTATION_ROTATE_90:
                    rotate = 90;
                    break;
            }
        }
        catch (IOException e)
        {
            Log.e("MainActivity", "ExifInterface IOException");
        }

        Matrix matrix = new Matrix();
        matrix.postRotate(rotate);
        return Bitmap.createBitmap(bitmap, 0, 0, bitmap.getWidth(), bitmap.getHeight(), matrix, true);
    }
    public void requestPermission() {

        if (ContextCompat.checkSelfPermission(this, Manifest.permission.WRITE_EXTERNAL_STORAGE) != PackageManager.PERMISSION_GRANTED ||
                ContextCompat.checkSelfPermission(this, Manifest.permission.READ_EXTERNAL_STORAGE) != PackageManager.PERMISSION_GRANTED) {

            Toast.makeText(this, "申请权限", Toast.LENGTH_SHORT).show();

            // 申请 相机 麦克风权限
            ActivityCompat.requestPermissions(this, new String[]{
                    Manifest.permission.WRITE_EXTERNAL_STORAGE,

                    Manifest.permission.READ_EXTERNAL_STORAGE}, 100);
        }
    }

（5）、添加手机存储器得读写权限

（6）、至此就完成了手机相册得打开和图片得获取 展示

二、图片保存功能（场景：从相册获得相片进行了检测、画框之后，然后在保存到相册中）

（1）、拖拽按钮得方法、修改界面布局、修改按钮

（2）、对应得代码布局文件

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout 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:orientation="vertical"
    android:layout_width="fill_parent"
    android:layout_height="fill_parent"
    tools:context=".MainActivity">

    <TextView
        android:id="@+id/sample_text"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text="Hello World!" />
    <LinearLayout
        android:orientation="horizontal"
        android:layout_width="fill_parent"
        android:layout_height="wrap_content">
    <Button
        android:id="@+id/button"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text="打开相册" />

    <Button
        android:id="@+id/button2"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text="保存图片" />
</LinearLayout>

    <ImageView
        android:id="@+id/imageView"
        android:layout_width="fill_parent"
        android:layout_height="fill_parent"
        android:layout_weight="1" />

</LinearLayout>

（3）、修改对应的保存图片代码

（4）、代码片段-1

Button saveImage = (Button) findViewById(R.id.button2);
        saveImage.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View arg0) {
                if (bitmap == null){
                    Toast.makeText(MainActivity.this,"请选择需要检测的图片",Toast.LENGTH_LONG).show();
                    return;
                }
                SimpleDateFormat format = new SimpleDateFormat("yyyyMMddHHmmssSSS");
                String fileName = "detected_" + format.format(new Date()) + ".jpg";
                Bitmap bmp = ((BitmapDrawable)imageView.getDrawable()).getBitmap();
                saveBitmap(bmp,fileName);
                Toast.makeText(MainActivity.this,"图片保存成功",Toast.LENGTH_LONG).show();
            }
        });

代码片段-2

public void saveBitmap(Bitmap bitmap, String bitName){
        String fileName;
        File file;
        if(Build.BRAND .equals("Xiaomi") ){
            fileName = Environment.getExternalStorageDirectory().getPath() + "/DCIM/Camera/" + bitName;
        }else{
            fileName = Environment.getExternalStorageDirectory().getPath() + "/DCIM/" + bitName;
        }
        file = new File(fileName);
        if(file.exists()){
            file.delete();
        }
        FileOutputStream out;
        try{
            out = new FileOutputStream(file);
            if(bitmap.compress(Bitmap.CompressFormat.JPEG, 90, out)){
                out.flush();
                out.close();
                MediaStore.Images.Media.insertImage(this.getContentResolver(), file.getAbsolutePath(), bitName, null);
            }
        } catch (IOException e){
            e.printStackTrace();
        }
        this.sendBroadcast(new Intent(Intent.ACTION_MEDIA_SCANNER_SCAN_FILE, Uri.parse("file://" + fileName)));
    }

（5）结果手机app