How to set an image in android app with sftp input stream?

问题

I'm using Android Studio to build an application. In this app, I want to get an image in a specific folder from a linux host using Jsch sftp, and set this new picture to an already-existing imageview.

But unfortunately the picture doesn't show up.

The following are the codes for this so far:

MainActivity.java

package com.example.picture_controller_2;

import android.graphics.drawable.Drawable;
import android.support.v7.app.AppCompatActivity;
import android.os.Bundle;
import android.app.Activity;
import java.io.BufferedInputStream;
import java.io.BufferedOutputStream;
import java.io.File;
import java.io.FileOutputStream;
import java.io.OutputStream;
import com.jcraft.jsch.Channel;
import com.jcraft.jsch.ChannelExec;
import com.jcraft.jsch.JSch;
import com.jcraft.jsch.JSchException;
import com.jcraft.jsch.Session;
import com.jcraft.jsch.ChannelSftp;
import android.view.View;
import android.os.AsyncTask;
import android.widget.ImageView;
import android.widget.Toast;

public class Button2Activity extends AppCompatActivity {

    private ImageView iv1;
    private Drawable ddd;

    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_button2);
        getSupportActionBar().setDisplayHomeAsUpEnabled(true);
    }

    public void show_picture_func (View v) {

        iv1 = (ImageView) findViewById(R.id.imageView1);

        new AsyncTask<Integer, Void, Void>(){
            @Override
            protected Void doInBackground(Integer... params) {

                String SFTPHOST = "192.168.0.1";
                int SFTPPORT = 22;
                String SFTPUSER = "pi";
                String SFTPPASS = "raspberry";
                String SFTPWORKINGDIR = "/home/pi/imgs/";

                Session session = null;
                Channel channel = null;
                ChannelSftp channelSftp = null;

                try {
                    JSch jsch = new JSch();
                    session = jsch.getSession(SFTPUSER, SFTPHOST, SFTPPORT);
                    session.setPassword(SFTPPASS);
                    session.setConfig("StrictHostKeyChecking", "no");
                    session.setTimeout(10000);
                    session.connect();
                    channel = session.openChannel("sftp");
                    channel.connect();
                    channelSftp = (ChannelSftp) channel;
                    channelSftp.cd(SFTPWORKINGDIR);
                    byte[] buffer = new byte[1024];
                    BufferedInputStream bis = new BufferedInputStream(channelSftp.get("AAP.jpg"));

                    Drawable ddd = Drawable.createFromStream(bis,"ddd");
                    bis.close();
                    // bos.close();
                } catch (Exception ex) {
                    ex.printStackTrace();
                }
                return null;
            }
        }.execute(1);

        iv1.setImageDrawable(ddd);
        //iv1.setScaleX(1);
        //iv1.setScaleY(1);
        Toast.makeText(getApplicationContext(), "Successful Download", Toast.LENGTH_LONG).show();
    }

}

activity_main.xml

<?xml version="1.0" encoding="utf-8"?>
<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:app="http://schemas.android.com/apk/res-auto"
    android:layout_width="match_parent" android:layout_height="match_parent">           

    <Button
        android:text="Show Picture"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_alignParentBottom="true"
        android:layout_centerHorizontal="true"
        android:layout_marginBottom="31dp"
        android:onClick="show_picture_func"
        android:id="@+id/button_show" />

    <ImageView
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        app:srcCompat="?android:attr/alertDialogIcon"
        android:layout_centerVertical="true"
        android:layout_centerHorizontal="true"
        android:id="@+id/imageView1"
        android:scaleX="5"
        android:scaleY="5" />

</RelativeLayout>

When I press the show picture button, the default picture of the imageview disappears, and it shows nothing. Also, this comes to logcat :

E/HW-JPEG-DEC: [HME_JPEG_DEC_Delete](3321): HME_JPEG_DEC_Delete: decoder_ctx=null

Note This error shows almost every time on all applications I write, but it doesn't have any effects ob them. I'm not sure about this one.

So, what is the problem? How can I solve this?

回答1:

First declare ddd just after:

new AsyncTask<Integer, Void, Void>(){

so:

new AsyncTask<Integer, Void, Void>(){

        Drawable ddd = null;

        @Override
        protected Void doInBackground(Integer... params) {

Then in doInBackround change the line:

Drawable ddd = Drawable.createFromStream(bis,"ddd");

to:

ddd = Drawable.createFromStream(bis,"ddd");

and finally move iv1.setImageDrawable(ddd); inside of onPostExecute of your AsyncTask (you must override it like you have done for doInBackground):

@Override
protected void onPostExecute(Void unused) {
    iv1.setImageDrawable(ddd);
}

回答2:

Use the following method to convert imageView drawable to input stream

void getInputStreamFromImageView(ImageView imageView) {
    Bitmap bitmap = ((BitmapDrawable) imageView.getDrawable()).getBitmap();
    ByteArrayOutputStream bos = new ByteArrayOutputStream();
    bitmap.compress(Bitmap.CompressFormat.PNG, 0 /*ignored for PNG*/, bos);
    byte[] bitmapdata = bos.toByteArray();
    ByteArrayInputStream bs = new ByteArrayInputStream(bitmapdata);
}

来源：https://stackoverflow.com/questions/47201504/how-to-set-an-image-in-android-app-with-sftp-input-stream