Android学习之调用摄像头和相册

调用摄像头：点击button——》启动相机程序——》传回照片——》显示照片
调用相册：点击button——》（如果没有访问SD卡权限，申请权限）打开相册——》选择照片——》传回照片——》（4.4及以上版本对封装的Uri解析）显示照片
URI(统一资源标识符)是用来标识某一互联网资源名称的字符串

从安装7.0之后直接使用本地真实路径的uri被认为是不安全的，会抛出异常，FileProvider是一种特殊的内容提供器，使用了和内容提供器类似的机制对数据进行保护，可以选择性的将封装过的uri共享给外部，从而提高了应用的安全性

访问SD卡的权限

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

Manifest中注册内容提供器

<application        ...        <provider            android:authorities="com.example.camera.fileprovider"            android:name="android.support.v4.content.FileProvider"            android:exported="false"            android:grantUriPermissions="true">            <meta-data                android:name="android.support.FILE_PROVIDER_PATHS"                android:resource="@xml/file_paths"/>        </provider>    </application>

新建xml目录，新建file_paths.xml

<?xml version="1.0" encoding="utf-8"?><paths xmlns:android="http://schemas.android.com/apk/res/android">    <external-path name="my_img" path=""/></paths>

layout：

<?xml version="1.0" encoding="utf-8"?><LinearLayout    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"    android:orientation="vertical"    tools:context="com.example.camera.MainActivity">    <Button        android:id="@+id/take_photo"        android:layout_width="match_parent"        android:layout_height="wrap_content"        android:text="Take Photo"/>    <Button        android:id="@+id/choose_from_album"        android:layout_width="match_parent"        android:layout_height="wrap_content"        android:text="Choose from album"/>    <ImageView        android:id="@+id/pic"        android:layout_width="wrap_content"        android:layout_height="wrap_content"        android:gravity="center_horizontal"/></LinearLayout>

MainActivity.java

...public class MainActivity extends AppCompatActivity implements View.OnClickListener{    public static final int TAKE_PHOTO = 1;    public static final int CHOOSE_PHOTO = 2;    private ImageView pic;    private Button take_photo,choose_photo;    private Uri imageUri;    @Override    protected void onCreate(Bundle savedInstanceState) {        super.onCreate(savedInstanceState);        setContentView(R.layout.activity_main);        pic = (ImageView) findViewById(R.id.pic);        take_photo = (Button) findViewById(R.id.take_photo);        take_photo.setOnClickListener(this);        choose_photo = (Button) findViewById(R.id.choose_from_album);        choose_photo.setOnClickListener(this);    }    @Override    protected void onActivityResult(int requestCode,int resultCode,Intent data){        switch (requestCode){            case TAKE_PHOTO: {                if (resultCode == RESULT_OK) {                    try {                        //显示照片                        Bitmap bitmap = BitmapFactory.decodeStream(getContentResolver().openInputStream(imageUri));                        pic.setImageBitmap(bitmap);                    } catch (FileNotFoundException e) {                        e.printStackTrace();                    }                }            }                break;            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                        handleImageOnKitKat(data);                    }else{                        handleImageBeforeKitKat(data);                    }                }            }                break;            default:                break;        }    }    /**     * 4.4及以上版本调用handleImageOnKitKat()方法，否则就调用handleImageBeforeKitKat()方法     * 4.4之后选取相册中的图片就不在返回图片真实的uri，而是一个封装的uri，4.4之后系统要对这个uri进行解析     */    @TargetApi(19)    private void handleImageOnKitKat(Intent data){        String imagePath = null;        Uri uri = data.getData();        if(DocumentsContract.isDocumentUri(this,uri)){            //如果是document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content类型的uri，则使用普通方法            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);    }    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;        //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;    }    private void displayImage(String imagePath){        if(imagePath != null){            Bitmap bitmap = BitmapFactory.decodeFile(imagePath);            pic.setImageBitmap(bitmap);        }else{            Toast.makeText(this,"打开图片失败",Toast.LENGTH_SHORT).show();        }    }    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 onClick(View view) {        switch(view.getId()){            case R.id.take_photo:{                //创建file对象，存储拍照后的照片                File outputImage = new File(getExternalCacheDir(),                        "output_image,jpg");                try{                    if(outputImage.exists()){                        outputImage.delete();                    }                    outputImage.createNewFile();                }catch (IOException e){                    e.printStackTrace();                }                if(Build.VERSION.SDK_INT >= 24){                    imageUri = FileProvider.getUriForFile(MainActivity.this,                            "com.example.camera.fileprovider",outputImage);                }else{                    imageUri = Uri.fromFile(outputImage);                }                //启动相机                Intent intent = new Intent("android.media.action.IMAGE_CAPTURE");                intent.putExtra(MediaStore.EXTRA_OUTPUT,imageUri);                startActivityForResult(intent,TAKE_PHOTO);            }                break;            case R.id.choose_from_album:{                //动态申请权限                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();                }            }        }    }}