一、需求

一个界面，界面上一个文本输入框、一个按钮、一个二维码显示view。可在文本输入框输入字符串，点击按钮后，生成二维码。

二、创建android stdio工程

三、设置好JDK

我开始使用JDK 11：

四、创建activity

得到：

五、编写activity_main.xml布局

<?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=".MainActivity">

    <EditText
        android:id="@+id/editText"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:layout_marginTop="50dp"
        android:hint="请输入要生成二维码的字符串" />

    <Button
        android:id="@+id/button"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:text="生成二维码" />

    <ImageView
        android:id="@+id/imageView"
        android:layout_width="match_parent"
        android:layout_height="match_parent" />

</LinearLayout>

六、build.gradle增加zxing依赖

七、MainActivity

package com.example.gen_qr_code;

import androidx.appcompat.app.AppCompatActivity;

import android.graphics.Bitmap;
import android.os.Bundle;
import android.text.TextUtils;
import android.view.View;
import android.widget.EditText;
import android.widget.ImageView;

import com.google.zxing.BarcodeFormat;
import com.google.zxing.WriterException;
import com.google.zxing.common.BitMatrix;
import com.google.zxing.qrcode.QRCodeWriter;

import java.nio.charset.StandardCharsets;

public class MainActivity extends AppCompatActivity {
    private EditText editText;
    private ImageView imageView;

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

        editText = findViewById(R.id.editText);
        imageView = findViewById(R.id.imageView);

        findViewById(R.id.button).setOnClickListener(v -> {
            String text = editText.getText().toString();
            byte[] utf8Bytes = text.getBytes(StandardCharsets.UTF_8);
            String utf8BytesString = new String(utf8Bytes, StandardCharsets.UTF_8);
            if (!TextUtils.isEmpty(utf8BytesString)) {
                Bitmap qrCode = null;
                try {
                    qrCode = createQRCode(utf8BytesString);
                } catch (WriterException e) {
                    throw new RuntimeException(e);
                }
                imageView.setImageBitmap(qrCode);
            }
        });
    }

    private Bitmap createQRCode(String text) throws WriterException {
        QRCodeWriter qrCodeWriter = new QRCodeWriter();
        BitMatrix bitMatrix = qrCodeWriter.encode(text, BarcodeFormat.QR_CODE, 300, 300);
        Bitmap bitmap = Bitmap.createBitmap(300, 300, Bitmap.Config.RGB_565);
        for (int x = 0; x < 300; x++) {
            for (int y = 0; y < 300; y++) {
                bitmap.setPixel(x, y, bitMatrix.get(x, y) ? getResources().getColor(R.color.black) : getResources().getColor(R.color.white));
            }
        }
        return bitmap;
    }
}

八、github