在设备屏幕上居中图像

Question

我有一个简单的方形图像来测试拖动缩放和旋转系统。 一切正常，但我在设备中心的图像中心出现问题，如图所示（矩阵图像相同......我在这里阅读了很多帖子，但没有找到解决方案）。使用下面的代码，图像在左上角。

xml 文件...

<?xml version="1.0" encoding="utf-8"?>

xmlns:app="http://schemas.android.com/apk/res-auto"
xmlns:tools="http://schemas.android.com/tools"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:background="@android:color/white"
tools:context="com.br1dev.myapplication.MainActivity">

<RelativeLayout

    android:layout_width="wrap_content"
    android:layout_height="wrap_content">

    <ImageView
        android:id="@+id/fullImage"
        android:layout_width="match_parent"
        android:layout_height="match_parent"
        android:layout_centerInParent="true"
        android:contentDescription="@android:string/untitled"
        android:scaleType="centerInside"
        app:srcCompat="@drawable/f1" />

</RelativeLayout>

和活动

public class MainActivity extends AppCompatActivity
{
ImageView fullImage;
float scalediff;
private static final int NONE = 0;
private static final int DRAG = 1;
private static final int ZOOM = 2;
private int mode = NONE;
private float oldDist = 1f;
private float d = 0f;
private float newRot = 0f;

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

    init();

    RelativeLayout.LayoutParams layoutParams = new RelativeLayout.LayoutParams(800, 800);
    layoutParams.topMargin = 0;
    layoutParams.bottomMargin = 0;
    layoutParams.rightMargin = 0;
    layoutParams.leftMargin = 0;

    fullImage.setLayoutParams(layoutParams);

    fullImage.setOnTouchListener(new View.OnTouchListener()
    {
        RelativeLayout.LayoutParams parms;
        int startwidth;
        int startheight;
        float dx = 0, dy = 0, x = 0, y = 0;
        float angle = 0;

        @Override
        public boolean onTouch(View v, MotionEvent event)
        {

            final ImageView view = (ImageView) v;

            ((BitmapDrawable) view.getDrawable()).setAntiAlias(true);
            switch (event.getAction() & MotionEvent.ACTION_MASK)
            {
                case MotionEvent.ACTION_DOWN:

                    parms = (RelativeLayout.LayoutParams) view.getLayoutParams();
                    startwidth = parms.width;
                    startheight = parms.height;
                    dx = event.getRawX() - parms.leftMargin;
                    dy = event.getRawY() - parms.topMargin;
                    mode = DRAG;
                    break;

                case MotionEvent.ACTION_POINTER_DOWN:

                    oldDist = spacing(event);
                    if (oldDist > 10f)
                    {
                        mode = ZOOM;
                    }

                    d = rotation(event);

                    break;

                case MotionEvent.ACTION_UP:

                    break;

                case MotionEvent.ACTION_POINTER_UP:

                    mode = NONE;

                    break;

                case MotionEvent.ACTION_MOVE:

                    if (mode == DRAG)
                    {
                        x = event.getRawX();
                        y = event.getRawY();

                        parms.leftMargin = (int) (x - dx);
                        parms.topMargin = (int) (y - dy);

                        parms.rightMargin = 0;
                        parms.bottomMargin = 0;
                        parms.rightMargin = parms.leftMargin + (5 * parms.width);
                        parms.bottomMargin = parms.topMargin + (10 * parms.height);

                        view.setLayoutParams(parms);

                    } else if (mode == ZOOM) {

                        if (event.getPointerCount() == 2)
                        {
                            newRot = rotation(event);
                            float r = newRot - d;
                            angle = r;

                            x = event.getRawX();
                            y = event.getRawY();

                            float newDist = spacing(event);
                            if (newDist > 10f)
                            {
                                float scale = newDist / oldDist * view.getScaleX();
                                if (scale > 0.6)
                                {
                                    scalediff = scale;
                                    view.setScaleX(scale);
                                    view.setScaleY(scale);
                                }
                            }

                            view.animate().rotationBy(angle).setDuration(0).setInterpolator(new LinearInterpolator()).start();

                            x = event.getRawX();
                            y = event.getRawY();

                            parms.leftMargin = (int) ((x - dx) + scalediff);
                            parms.topMargin = (int) ((y - dy) + scalediff);

                            parms.rightMargin = 0;
                            parms.bottomMargin = 0;
                            parms.rightMargin = parms.leftMargin + (5 * parms.width);
                            parms.bottomMargin = parms.topMargin + (10 * parms.height);

                            view.setLayoutParams(parms);
                        }
                    }
                    break;
            }
            return true;
        }
    });
}

private void init()
{
    fullImage = findViewById(R.id.fullImage);
}

private float spacing(MotionEvent event)
{
    float x = event.getX(0) - event.getX(1);
    float y = event.getY(0) - event.getY(1);
    return (float) Math.sqrt(x * x + y * y);
}

private float rotation(MotionEvent event)
{
    double delta_x = (event.getX(0) - event.getX(1));
    double delta_y = (event.getY(0) - event.getY(1));
    double radians = Math.atan2(delta_y, delta_x);
    return (float) Math.toDegrees(radians);
}
}

Answer 1

在RelativeLayout 中，添加android:layout_centerInParent="true"。

<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:layout_width="match_parent"
    android:layout_height="match_parent" >

    <ImageView android:id="@+id/imageView1"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:src="@drawable/icon"
        android:scaleType="centerInside"
        android:layout_centerInParent="true" />

</RelativeLayout>

Answer 2

由于您正在以编程方式为图像视图分配一组新的布局参数：

RelativeLayout.LayoutParams layoutParams = new RelativeLayout.LayoutParams(800, 800);
layoutParams.topMargin = 0;
layoutParams.bottomMargin = 0;
layoutParams.rightMargin = 0;
layoutParams.leftMargin = 0;

fullImage.setLayoutParams(layoutParams);

您之前使用的此布局中（在 .xml 中）的图像视图上的每个约束都将重置为默认值，并且您必须以编程方式再次包含约束。例如，在您的代码中，您忘记添加 centerInParent 约束，因此包括 centerInParent 并更改宽度和高度以匹配父项：

RelativeLayout.LayoutParams layoutParams = new RelativeLayout.LayoutParams(ViewGroup.LayoutParams.MATCH_PARENT, ViewGroup.LayoutParams.MATCH_PARENT);
    layoutParams.addRule(RelativeLayout.CENTER_IN_PARENT);
    layoutParams.topMargin = 0;
    layoutParams.bottomMargin = 0;
    layoutParams.rightMargin = 0;
    layoutParams.leftMargin = 0;

    fullImage.setLayoutParams(layoutParams);

结果符合预期：