Die Anleitung zu Android ImageView

<?xml version="1.0" encoding="utf-8"?>
<androidx.constraintlayout.widget.ConstraintLayout
    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:layout_width="match_parent"
    android:layout_height="match_parent"
    tools:context=".MainActivity">

    <ImageView
        android:id="@+id/imageView"
        android:layout_width="375dp"
        android:layout_height="207dp"
        android:layout_marginStart="16dp"
        android:layout_marginLeft="16dp"
        android:layout_marginTop="17dp"
        android:layout_marginEnd="16dp"
        android:layout_marginRight="16dp"
        app:layout_constraintEnd_toEndOf="parent"
        app:layout_constraintStart_toStartOf="parent"
        app:layout_constraintTop_toTopOf="parent"
        app:srcCompat="@drawable/ic_launcher_foreground"
        tools:ignore="VectorDrawableCompat" />

    <LinearLayout
        android:layout_width="0dp"
        android:layout_height="wrap_content"
        android:layout_marginStart="16dp"
        android:layout_marginLeft="16dp"
        android:layout_marginTop="16dp"
        android:layout_marginEnd="16dp"
        android:layout_marginRight="16dp"
        android:orientation="horizontal"
        app:layout_constraintEnd_toEndOf="parent"
        app:layout_constraintStart_toStartOf="parent"
        app:layout_constraintTop_toBottomOf="@+id/imageView">

        <Space
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:layout_weight="1" />

        <Button
            android:id="@+id/button1"
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:layout_weight="0"
            android:text="Show Image 1" />

        <Button
            android:id="@+id/button2"
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:layout_weight="0"
            android:text="Show Image 2" />

        <Space
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:layout_weight="1" />
    </LinearLayout>
</androidx.constraintlayout.widget.ConstraintLayout>

package org.o7planning.androidimageview;

import androidx.appcompat.app.AppCompatActivity;

import android.os.Bundle;
import android.view.View;
import android.widget.Button;
import android.widget.ImageView;

public class MainActivity extends AppCompatActivity {


    private ImageView imageView;
    private Button button1;
    private Button button2;

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

        this.imageView = (ImageView) this.findViewById(R.id.imageView);

        this.button1 = (Button) this.findViewById(R.id.button1);
        this.button2 = (Button) this.findViewById(R.id.button2);

        this.button1.setOnClickListener(new Button.OnClickListener() {

            @Override
            public void onClick(View v) {
                showImage1();
            }
        });

        this.button2.setOnClickListener(new Button.OnClickListener() {

            @Override
            public void onClick(View v) {
                showImage2();
            }
        });
    }


    private void showImage1() {
        this.imageView.setImageResource(R.drawable.triceratops_1);
    }

    private void showImage2() {
        this.imageView.setImageResource(R.drawable.triceratops_2);
    }

}

URL url = new URL(imageUrl);
HttpURLConnection httpConn = (HttpURLConnection) url.openConnection();

httpConn.connect();
int resCode = httpConn.getResponseCode();

if (resCode == HttpURLConnection.HTTP_OK) {
  InputStream in = httpConn.getInputStream();
  Bitmap bitmap = BitmapFactory.decodeStream(in);

  this.imageView.setImageBitmap(bitmap);
}

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

File imgFile = new  File("/sdcard/Images/mypicture.png");

if(imgFile.exists()) {

   Bitmap myBitmap = BitmapFactory.decodeFile(imgFile.getAbsolutePath());

   this.imageView.setImageBitmap(myBitmap);

}