android studio 调用系统相机

1. 在AndroidManifest.xml文件中添加相机权限：

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

2. 创建一个Intent对象，设置Action为MediaStore.ACTION_IMAGE_CAPTURE：

Intent intent = new Intent(MediaStore.ACTION_IMAGE_CAPTURE);

3. 创建一个File对象，用于保存拍摄的照片：

File photoFile = null;
try {
    photoFile = createImageFile();
} catch (IOException ex) {
    // Error occurred while creating the File
    ex.printStackTrace();
}
if (photoFile != null) {
    Uri photoURI = FileProvider.getUriForFile(this, "com.your.package.name.fileprovider", photoFile);
    intent.putExtra(MediaStore.EXTRA_OUTPUT, photoURI);
}

其中，createImageFile()方法用于创建一个临时文件来存储拍摄的照片：

private File createImageFile() throws IOException {
    // Create an image file name
    String timeStamp = new SimpleDateFormat("yyyyMMdd_HHmmss").format(new Date());
    String imageFileName = "JPEG_" + timeStamp + "_";
    File storageDir = getExternalFilesDir(Environment.DIRECTORY_PICTURES);
    File image = File.createTempFile(
        imageFileName,  /* prefix */
        ".jpg",         /* suffix */
        storageDir      /* directory */
    );

    // Save a file: path for use with ACTION_VIEW intents
    mCurrentPhotoPath = image.getAbsolutePath();
    return image;
}

注意，需要在AndroidManifest.xml文件中定义一个FileProvider：

<provider
    android:name="androidx.core.content.FileProvider"
    android:authorities="com.your.package.name.fileprovider"
    android:grantUriPermissions="true"
    android:exported="false">
    <meta-data
        android:name="android.support.FILE_PROVIDER_PATHS"
        android:resource="@xml/file_paths" />
</provider>

还需要在res/xml目录下创建一个file_paths.xml文件，用于指定临时文件存储的路径：

<paths xmlns:android="http://schemas.android.com/apk/res/android">
    <external-files-path name="my_images" path="Pictures" />
</paths>

4. 调用startActivityForResult()方法启动相机：

startActivityForResult(intent, REQUEST_IMAGE_CAPTURE);

5. 在onActivityResult()方法中处理拍摄完成后的结果：

@Override
protected void onActivityResult(int requestCode, int resultCode, Intent data) {
    if (requestCode == REQUEST_IMAGE_CAPTURE && resultCode == RESULT_OK) {
        // Image captured and saved to fileUri specified in the Intent
        Toast.makeText(this, "Image saved to file: " + mCurrentPhotoPath, Toast.LENGTH_SHORT).show();
        // TODO: Do something with the image
    }
}