android - 在 ImageView 中选择图像的一部分并检索所选矩形的端点

Question

我需要拖动并选择 ImageView 中的图像集的一部分，并检索所选矩形的端点而不进行任何修改(例如裁剪)。

到目前为止，我所能做的就是找出用户点击屏幕的点的坐标。

ImageView imageView = (ImageView) findViewById(R.id.imageView);
imageView.setOnTouchListener(new View.OnTouchListener() {
    @Override
    public boolean onTouch(View v, MotionEvent event) {
        //Simply displays a toast
        Utilities.displayToast(getApplicationContext(), "Touch coordinates : " +
                String.valueOf(event.getX()) + "x" + String.valueOf(event.getY())); 
        return true;
    }
});

但这离我想去的地方还很远。而且我真的没能在 StackOverFlow/Google 上找到任何相关内容。

我该如何实现？

Answer 1

这是您可以使用的一种方法(但是，有很多方法可以实现相同的方法)。它基于创建用于绘制和跟踪选择矩形的自定义 View 。此外，您可以在您的 OnTouchListener() 中应用来自自定义 View 的 onTouch() 的逻辑。

主要布局:

<RelativeLayout
    xmlns:android="http://schemas.android.com/apk/res/android"
    android:layout_height="match_parent"
    android:layout_width="match_parent"
    android:id="@+id/root"
    android:background="@android:color/background_dark">

    <ImageView
        android:layout_width="match_parent"
        android:layout_height="match_parent"
        android:id="@+id/image"
        android:src="@drawable/up_image"
        android:scaleType="fitXY" />

    <com.example.TestApp.DragRectView
        android:layout_width="match_parent"
        android:layout_height="match_parent"
        android:id="@+id/dragRect" />

</RelativeLayout>

自定义 View :

import android.content.Context;
import android.graphics.Canvas;
import android.graphics.Paint;
import android.graphics.Rect;
import android.text.TextPaint;
import android.util.AttributeSet;
import android.view.MotionEvent;
import android.view.View;

public class DragRectView extends View {

    private Paint mRectPaint;

    private int mStartX = 0;
    private int mStartY = 0;
    private int mEndX = 0;
    private int mEndY = 0;
    private boolean mDrawRect = false;
    private TextPaint mTextPaint = null;

    private OnUpCallback mCallback = null;

    public interface OnUpCallback {
        void onRectFinished(Rect rect);
    }

    public DragRectView(final Context context) {
        super(context);
        init();
    }

    public DragRectView(final Context context, final AttributeSet attrs) {
        super(context, attrs);
        init();
    }

    public DragRectView(final Context context, final AttributeSet attrs, final int defStyle) {
        super(context, attrs, defStyle);
        init();
    }

    /**
     * Sets callback for up
     *
     * @param callback {@link OnUpCallback}
     */
    public void setOnUpCallback(OnUpCallback callback) {
        mCallback = callback;
    }

    /**
     * Inits internal data
     */
    private void init() {
        mRectPaint = new Paint();
        mRectPaint.setColor(getContext().getResources().getColor(android.R.color.holo_green_light));
        mRectPaint.setStyle(Paint.Style.STROKE);
        mRectPaint.setStrokeWidth(5); // TODO: should take from resources

        mTextPaint = new TextPaint();
        mTextPaint.setColor(getContext().getResources().getColor(android.R.color.holo_green_light));
        mTextPaint.setTextSize(20);
    }

    @Override
    public boolean onTouchEvent(final MotionEvent event) {

        // TODO: be aware of multi-touches
        switch (event.getAction()) {
            case MotionEvent.ACTION_DOWN:
                mDrawRect = false;
                mStartX = (int) event.getX();
                mStartY = (int) event.getY();
                invalidate();
                break;

            case MotionEvent.ACTION_MOVE:
                final int x = (int) event.getX();
                final int y = (int) event.getY();

                if (!mDrawRect || Math.abs(x - mEndX) > 5 || Math.abs(y - mEndY) > 5) {
                    mEndX = x;
                    mEndY = y;
                    invalidate();
                }

                mDrawRect = true;
                break;

            case MotionEvent.ACTION_UP:
                if (mCallback != null) {
                    mCallback.onRectFinished(new Rect(Math.min(mStartX, mEndX), Math.min(mStartY, mEndY),
                            Math.max(mEndX, mStartX), Math.max(mStartY, mEndY)));
                }
                invalidate();
                break;

            default:
                break;
        }

        return true;
    }

    @Override
    protected void onDraw(final Canvas canvas) {
        super.onDraw(canvas);

        if (mDrawRect) {
            canvas.drawRect(Math.min(mStartX, mEndX), Math.min(mStartY, mEndY),
                    Math.max(mEndX, mStartX), Math.max(mEndY, mStartY), mRectPaint);
            canvas.drawText("  (" + Math.abs(mStartX - mEndX) + ", " + Math.abs(mStartY - mEndY) + ")",
                    Math.max(mEndX, mStartX), Math.max(mEndY, mStartY), mTextPaint);
        }
    }
}

Activity 很简单:

public class MyActivity extends Activity {

    private static final String TAG = "MyActivity";

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

        final DragRectView view = (DragRectView) findViewById(R.id.dragRect);

        if (null != view) {
            view.setOnUpCallback(new DragRectView.OnUpCallback() {
                @Override
                public void onRectFinished(final Rect rect) {
                    Toast.makeText(getApplicationContext(), "Rect is (" + rect.left + ", " + rect.top + ", " + rect.right + ", " + rect.bottom + ")",
                            Toast.LENGTH_LONG).show();
                }
            });
        }
    }
}

输出如下: