imread不从Linux读取Java Android上的现有映像

Question

package com.example.cppinandroid;
import androidx.appcompat.app.AppCompatActivity;
import android.os.Bundle;
import android.util.Log;
import android.widget.TextView;
import org.opencv.core.Mat;
import java.io.File;
import static org.opencv.imgcodecs.Imgcodecs.CV_LOAD_IMAGE_GRAYSCALE;
import org.opencv.imgcodecs.Imgcodecs;

public class MainActivity extends AppCompatActivity
{
    @Override
    protected void onCreate(Bundle savedInstanceState) 
    {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);

        TextView tv = findViewById( R.id.sample_text );

        Mat image;
        image = Imgcodecs.imread( "/home/<myName>/a.png", CV_LOAD_IMAGE_GRAYSCALE);
        if ( image.size().height > 0 )
        {
            tv.setText( "No datfa in image!");
        }
        else
        {
            tv.setText( "xxff " + image.size().height);
        }
    }
}

我没有使用任何可提取或外部媒体。图像存在于主文件夹中，可以通过提供完全相同的路径由普通的opencv C++程序打开。

这里有人告诉我原生C++NDK将无法读取Linux路径。好吧。这里都是Java。

当我执行它时，它总是在else语句中运行，并将高度显示为0.0。

我已经删除了多余的代码。

在Linux上的这个程序中，从主文件夹读取一个普通的png的方法是什么？

Answer 1

看到这个示例代码，也许可以帮助你，我测试了这个代码，为我工作，我可以得到任何图像的宽度和高度。

1）首先，您需要将OpenCVLibrary导入到您的项目中：see this link-link

2）然后您需要对应用程序设置read_external_storage权限：plz在androidmanifest.xml上添加此命令：

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

3）您需要文件选取器来获取特定的文件我使用ru.bartwell:exfilepicker:Link

implementation 'ru.bartwell:exfilepicker:2.1'

4）最后，您只需将以下简单代码添加到mainactivity:

    private static final int READ_STORAGE_PERMISSION_REQUEST_CODE = 1;
    private static final int EX_FILE_PICKER_RESULT = 0;

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

        initLoadOpenCV();

        if (!checkPermissionForReadExtertalStorage()) {
            requestPermissionForReadExtertalStorage();
        }

    }

    private void initLoadOpenCV() {
        boolean isDebug = OpenCVLoader.initDebug();
        if (isDebug) {
            Log.i("init Opencv", "init openCV success!!");
        } else {
            Log.e("init Opencv", "init openCV failure!!");
        }
    }

    @Override
    public void onActivityResult(int requestCode, int resultCode, Intent data) {
        if (requestCode == EX_FILE_PICKER_RESULT) {
            ExFilePickerResult result = ExFilePickerResult.getFromIntent(data);
            if (result != null && result.getCount() > 0) {
                // Here is object contains selected files names and path
                Log.i("folderLocation", result.getPath() + result.getNames().get(0));

                Mat srcMat1 = Imgcodecs.imread(result.getPath() + result.getNames().get(0));
                if (srcMat1.empty()) {
                    return;
                }

                int width = srcMat1.width();
                int height = srcMat1.height();
                int type = srcMat1.type();
                Log.i("width", srcMat1.width() + "");
                Log.i("height", srcMat1.height() + "");
                Log.i("type", srcMat1.type() + "");

            }
        }
    }

    public boolean checkPermissionForReadExtertalStorage() {
        if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.M) {
            int result = getApplicationContext().checkSelfPermission(Manifest.permission.READ_EXTERNAL_STORAGE);
            return result == PackageManager.PERMISSION_GRANTED;
        }
        return false;
    }

    public void requestPermissionForReadExtertalStorage() {
        ActivityCompat.requestPermissions(this, new String[]{Manifest.permission.READ_EXTERNAL_STORAGE},
                READ_STORAGE_PERMISSION_REQUEST_CODE);
    }

    @Override
    public void onRequestPermissionsResult(int requestCode, String permissions[], int[] grantResults) {
        switch (requestCode) {
            case READ_STORAGE_PERMISSION_REQUEST_CODE:
                if (grantResults.length > 0 && grantResults[0] == PackageManager.PERMISSION_GRANTED) {
                    Log.e("value", "Permission Granted, Now you can use local drive .");

                    ExFilePicker exFilePicker = new ExFilePicker();
                    exFilePicker.start(this, EX_FILE_PICKER_RESULT);
                } else {
                    Log.e("value", "Permission Denied, You cannot use local drive .");
                    requestPermissionForReadExtertalStorage();
                }
                break;
        }
    }