Android：图片中叠加文字，支持拖动改变位置

之所以做了这么一个Demo，是由于近期项目中有一个奇葩的需求：用户拍摄照片后，分享到微信的同一时候加入备注，想获取用户在微信的弹出框输入的内容。保存在自己的server上。而其实，这个内容程序是无法获取的，因此採取了一个折衷方案，将文字直接写在图片上。

首先上Demo效果图：

功能：

1.用户自由输入内容，可手动换行，而且行满也会自己主动换行。

2.可拖动改变图片中文本位置（文字不会超出图片区域）。

3.点击“生成图片”button之后，生成一张带有文字的图片文件。

代码不多，直接所有贴上了：

Activity:

/**
 * 将文字写在图片中（截图方式）,支持拖动文字。
<br/>
 * 说明：非常明显，截图方式会减少图片的质量。假设须要保持图片质量能够使用canvas的方式。将文字直接绘制在图片之上(只是，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卡根文件夹/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（相似于截图）
    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;
    }
}

<?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="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="加入备注" />

    <Button
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:onClick="confirm"
        android:text="生成图片" />

</LinearLayout>