Android开发中如何实现一个图片中叠加文字功能

/**
 * 将文字写在图片中（截图方式）,支持拖动文字。<br/>
 * 说明：很明显，截图方式会降低图片的质量。如果需要保持图片质量可以使用canvas的方式，将文字直接绘制在图片之上(不过，使用此方式要实现文字拖动较为复杂)。
 */
public class MainActivity extends AppCompatActivity {
  //图片组件
  private ImageView imageView;
  //位于图片中的文本组件
  private TextView tvInImage;
  //图片和文本的父组件
  private View containerView;
  //父组件的尺寸
  private float imageWidth, imageHeight, imagePositionX, imagePositionY;
  @Override
  protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.image_with_text);
    imageView = (ImageView) findViewById(R.id.writeText_img);
    EditText editText = (EditText) findViewById(R.id.writeText_et);
    tvInImage = (TextView) findViewById(R.id.writeText_image_tv);
    containerView = findViewById(R.id.writeText_img_rl);
    imageView.getViewTreeObserver().addOnGlobalLayoutListener(new ViewTreeObserver.OnGlobalLayoutListener() {
      @Override
      public void onGlobalLayout() {
        imageView.getViewTreeObserver().removeOnGlobalLayoutListener(this);
        imagePositionX = imageView.getX();
        imagePositionY = imageView.getY();
        imageWidth = imageView.getWidth();
        imageHeight = imageView.getHeight();
        //设置文本大小
        tvInImage.setMaxWidth((int) imageWidth);
      }
    });
    imageView.setImageBitmap(getScaledBitmap(R.mipmap.test_img));
    //输入框
    editText.addTextChangedListener(new TextWatcher() {
      @Override
      public void beforeTextChanged(CharSequence s, int start, int count, int after) {
      }
      @Override
      public void onTextChanged(CharSequence s, int start, int before, int count) {
        if (s.toString().equals("")) {
          tvInImage.setVisibility(View.INVISIBLE);
        } else {
          tvInImage.setVisibility(View.VISIBLE);
          tvInImage.setText(s);
        }
      }
      @Override
      public void afterTextChanged(Editable s) {
      }
    });
    final GestureDetector gestureDetector = new GestureDetector(this, new SimpleGestureListenerImpl());
    //移动
    tvInImage.setOnTouchListener(new View.OnTouchListener() {
      @Override
      public boolean onTouch(View v, MotionEvent event) {
        gestureDetector.onTouchEvent(event);
        return true;
      }
    });
  }
  //确认，生成图片
  public void confirm(View view) {
    Bitmap bm = loadBitmapFromView(containerView);
    String filePath = Environment.getExternalStorageDirectory() + File.separator + "image_with_text.jpg";
    try {
      bm.compress(Bitmap.CompressFormat.JPEG, 100, new FileOutputStream(filePath));
      Toast.makeText(this, "图片已保存至：SD卡根目录/image_with_text.jpg", Toast.LENGTH_LONG).show();
    } catch (FileNotFoundException e) {
      e.printStackTrace();
    }
  }
  //以图片形式获取View显示的内容（类似于截图）
  public static Bitmap loadBitmapFromView(View view) {
    Bitmap bitmap = Bitmap.createBitmap(view.getWidth(), view.getHeight(), Bitmap.Config.ARGB_8888);
    Canvas canvas = new Canvas(bitmap);
    view.draw(canvas);
    return bitmap;
  }
  private int count = 0;
  //tvInImage的x方向和y方向移动量
  private float mDx, mDy;
  //移动
  private class SimpleGestureListenerImpl extends GestureDetector.SimpleOnGestureListener {
    @Override
    public boolean onScroll(MotionEvent e1, MotionEvent e2, float distanceX, float distanceY) {
      //向右移动时，distanceX为负；向左移动时，distanceX为正
      //向下移动时，distanceY为负；向上移动时，distanceY为正
      count++;
      mDx -= distanceX;
      mDy -= distanceY;
      //边界检查
      mDx = calPosition(imagePositionX - tvInImage.getX(), imagePositionX + imageWidth - (tvInImage.getX() + tvInImage.getWidth()), mDx);
      mDy = calPosition(imagePositionY - tvInImage.getY(), imagePositionY + imageHeight - (tvInImage.getY() + tvInImage.getHeight()), mDy);
      //控制刷新频率
      if (count % 5 == 0) {
        tvInImage.setX(tvInImage.getX() + mDx);
        tvInImage.setY(tvInImage.getY() + mDy);
      }
      return true;
    }
  }
  //计算正确的显示位置（不能超出边界）
  private float calPosition(float min, float max, float current) {
    if (current < min) {
      return min;
    }
    if (current > max) {
      return max;
    }
    return current;
  }
  //获取压缩后的bitmap
  private Bitmap getScaledBitmap(int resId) {
    BitmapFactory.Options opt = new BitmapFactory.Options();
    opt.inJustDecodeBounds = true;
    BitmapFactory.decodeResource(getResources(), resId, opt);
    opt.inSampleSize = Utility.calculateInSampleSize(opt, 600, 800);
    opt.inJustDecodeBounds = false;
    return BitmapFactory.decodeResource(getResources(), resId, opt);
  }
}

public class Utility {
  //计算 inSampleSize 值，压缩图片
  public static int calculateInSampleSize(BitmapFactory.Options options, int reqWidth, int reqHeight) {
    // Raw height and width of image
    final int height = options.outHeight;
    final int width = options.outWidth;
    int inSampleSize = 1;
    if (height > reqHeight || width > reqWidth) {
      final int halfHeight = height / 2;
      final int halfWidth = width / 2;
      // Calculate the largest inSampleSize value that is a power of 2 and keeps both
      // height and width larger than the requested height and width.
      while ((halfHeight / inSampleSize) > reqHeight && (halfWidth / inSampleSize) > reqWidth) {
        inSampleSize *= 2;
      }
    }
    return inSampleSize;
  }
}

<&#63;xml version="1.0" encoding="utf-8"&#63;>
<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="10dp">
  <RelativeLayout
    android:id="@+id/writeText_img_rl"
    android:layout_width="wrap_content"
    android:layout_height="wrap_content"
    android:layout_gravity="center_horizontal">
    <ImageView
      android:id="@+id/writeText_img"
      android:layout_width="wrap_content"
      android:layout_height="wrap_content"
      android:maxHeight="360dp"
      android:adjustViewBounds="true"
      android:contentDescription="@null"/>
    <TextView
      android:id="@+id/writeText_image_tv"
      android:layout_width="wrap_content"
      android:layout_height="wrap_content"
      android:visibility="invisible"
      android:layout_centerInParent="true"
      android:background="#79652a"
      android:clickable="true"
      android:padding="4dp"
      android:textColor="@android:color/white"
      android:textSize="15sp" />
  </RelativeLayout>
  <EditText
    android:id="@+id/writeText_et"
    android:layout_width="match_parent"
    android:layout_height="wrap_content"
    android:layout_marginTop="8dp"
    android:hint="添加备注" />
  <Button
    android:layout_width="wrap_content"
    android:layout_height="wrap_content"
    android:onClick="confirm"
    android:text="生成图片" />
</LinearLayout>