// ===================== 文件：MainActivity.java =====================
package com.example.imagewatermark;
 
import android.content.Intent;
import android.graphics.Bitmap;
import android.net.Uri;
import android.os.Bundle;
import android.provider.MediaStore;
import android.widget.Button;
import android.widget.ImageView;
import android.widget.Toast;
import androidx.activity.result.ActivityResultLauncher;
import androidx.activity.result.contract.ActivityResultContracts;
import androidx.annotation.Nullable;
import androidx.appcompat.app.AppCompatActivity;
 
import java.io.File;
import java.io.FileOutputStream;
 
/**
 * 主頁面：選擇圖片并添加水印
 */
public class MainActivity extends AppCompatActivity {
 
    private Button btnSelectImage;
    private Button btnAddTextWatermark;
    private Button btnAddImageWatermark;
    private ImageView imageView;
 
    private Bitmap selectedBitmap;
 
    // 文件選擇器
    private ActivityResultLauncher<String> imagePickerLauncher =
            registerForActivityResult(new ActivityResultContracts.GetContent(), uri -> {
                if (uri != null) {
                    try {
                        selectedBitmap = MediaStore.Images.Media.getBitmap(getContentResolver(), uri);
                        imageView.setImageBitmap(selectedBitmap);
                        Toast.makeText(this, "選擇圖片成功", Toast.LENGTH_SHORT).show();
                    } catch (Exception e) {
                        e.printStackTrace();
                    }
                }
            });
 
    @Override
    protected void onCreate(@Nullable Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
 
        btnSelectImage = findViewById(R.id.btn_select_image);
        btnAddTextWatermark = findViewById(R.id.btn_add_text_watermark);
        btnAddImageWatermark = findViewById(R.id.btn_add_image_watermark);
        imageView = findViewById(R.id.image_view);
 
        // 選擇圖片
        btnSelectImage.setOnClickListener(v -> {
            imagePickerLauncher.launch("image/*");
        });
 
        // 添加文字水印
        btnAddTextWatermark.setOnClickListener(v -> {
            if (selectedBitmap == null) {
                Toast.makeText(this, "請先選擇圖片", Toast.LENGTH_SHORT).show();
                return;
            }
            Bitmap watermarked = WatermarkUtils.addTextWatermark(selectedBitmap, "MyWatermark", 50, 50);
            imageView.setImageBitmap(watermarked);
            saveBitmap(watermarked, "text_watermark.png");
        });
 
        // 添加圖片水印
        btnAddImageWatermark.setOnClickListener(v -> {
            if (selectedBitmap == null) {
                Toast.makeText(this, "請先選擇圖片", Toast.LENGTH_SHORT).show();
                return;
            }
            Bitmap watermarkLogo = WatermarkUtils.decodeResource(this, R.drawable.logo);
            Bitmap watermarked = WatermarkUtils.addImageWatermark(selectedBitmap, watermarkLogo, 50, 50);
            imageView.setImageBitmap(watermarked);
            saveBitmap(watermarked, "image_watermark.png");
        });
    }
 
    /**
     * 保存 Bitmap 到本地文件
     */
    private void saveBitmap(Bitmap bitmap, String fileName) {
        try {
            File output = new File(getExternalFilesDir(null), fileName);
            FileOutputStream out = new FileOutputStream(output);
            bitmap.compress(Bitmap.CompressFormat.PNG, 100, out);
            out.flush();
            out.close();
            Toast.makeText(this, "保存成功：" + output.getAbsolutePath(), Toast.LENGTH_LONG).show();
        } catch (Exception e) {
            e.printStackTrace();
        }
    }
}
 
 
// ===================== 文件：WatermarkUtils.java =====================
package com.example.imagewatermark;
 
import android.content.Context;
import android.graphics.*;
import android.graphics.drawable.BitmapDrawable;
import android.graphics.drawable.Drawable;
 
public class WatermarkUtils {
 
    /**
     * 添加文字水印
     * @param src 原始圖片
     * @param text 水印文字
     * @param x X坐標
     * @param y Y坐標
     * @return 新的帶水印圖片
     */
    public static Bitmap addTextWatermark(Bitmap src, String text, int x, int y) {
        Bitmap result = src.copy(Bitmap.Config.ARGB_8888, true);
        Canvas canvas = new Canvas(result);
        Paint paint = new Paint();
        paint.setColor(Color.RED); // 水印顏色
        paint.setTextSize(60); // 字體大小
        paint.setAlpha(180); // 透明度
        paint.setAntiAlias(true); // 抗鋸齒
        canvas.drawText(text, x, y, paint);
        return result;
    }
 
    /**
     * 添加圖片水印
     * @param src 原始圖片
     * @param watermark 水印圖片
     * @param x X坐標
     * @param y Y坐標
     * @return 新的帶水印圖片
     */
    public static Bitmap addImageWatermark(Bitmap src, Bitmap watermark, int x, int y) {
        Bitmap result = src.copy(Bitmap.Config.ARGB_8888, true);
        Canvas canvas = new Canvas(result);
        Paint paint = new Paint();
        paint.setAlpha(180); // 透明度
        canvas.drawBitmap(watermark, x, y, paint);
        return result;
    }
 
    /**
     * 將資源文件轉(zhuǎn)換為 Bitmap
     */
    public static Bitmap decodeResource(Context context, int resId) {
        Drawable drawable = context.getResources().getDrawable(resId);
        if (drawable instanceof BitmapDrawable) {
            return ((BitmapDrawable) drawable).getBitmap();
        }
        return null;
    }
}
 
 
// ===================== 文件：res/layout/activity_main.xml =====================
<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:orientation="vertical"
    android:padding="20dp">
 
    <Button
        android:id="@+id/btn_select_image"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:text="選擇圖片" />
 
    <Button
        android:id="@+id/btn_add_text_watermark"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:text="添加文字水印"
        android:layout_marginTop="20dp"/>
 
    <Button
        android:id="@+id/btn_add_image_watermark"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:text="添加圖片水印"
        android:layout_marginTop="20dp"/>
 
    <ImageView
        android:id="@+id/image_view"
        android:layout_width="match_parent"
        android:layout_height="400dp"
        android:layout_marginTop="20dp"
        android:scaleType="fitCenter"/>
</LinearLayout>