java - 移动不适合手指的 View

Question

我正在做一个用户可以用手指触摸移动 View 的项目。它有效但对手指位置不准确。我不是在问你有什么好的代码，而是想知道为什么我的代码使 View 不适合手指。这就像 View 有大约 20dp 的更多边距。这是代码:

activity_main.xml

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout
    xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:tools="http://schemas.android.com/tools"
    android:id="@+id/lyRoot"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:paddingBottom="@dimen/activity_vertical_margin"
    android:paddingLeft="@dimen/activity_horizontal_margin"
    android:paddingRight="@dimen/activity_horizontal_margin"
    android:paddingTop="@dimen/activity_vertical_margin"
    tools:context="com.zihadrizkyef.dragviewwithfinger.MainActivity">

    <TextView
        android:id="@+id/tvText"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_margin="0dp"
        android:text="Hello World!"/>
</LinearLayout>

MainActivity.java

package com.zihadrizkyef.dragviewwithfinger;

import android.support.v7.app.AppCompatActivity;
import android.os.Bundle;
import android.view.MotionEvent;
import android.view.View;
import android.view.ViewGroup;
import android.widget.LinearLayout;
import android.widget.TextView;

public class MainActivity extends AppCompatActivity implements View.OnTouchListener {
    ViewGroup lyRoot;
    TextView tvText;
    LinearLayout.LayoutParams layoutParams;

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

        lyRoot = (ViewGroup)findViewById(R.id.lyRoot);
        tvText = (TextView)findViewById(R.id.tvText);
        layoutParams = (LinearLayout.LayoutParams)tvText.getLayoutParams();

        lyRoot.setOnTouchListener(this);
    }

    @Override
    public boolean onTouch(View v, MotionEvent event) {
        int x = (int)event.getRawX();
        int y = (int)event.getRawY();
        if (event.getAction() == MotionEvent.ACTION_MOVE) {
            layoutParams.leftMargin = x;
            layoutParams.topMargin = y;
            tvText.setLayoutParams(layoutParams);
        }
        lyRoot.invalidate();

        if (event.getAction() == MotionEvent.ACTION_UP) {
            System.out.println("mouseX:"+x+" ; mouseY:"+y);
            System.out.println("viewX:"+layoutParams.leftMargin+" ; viewY:"+layoutParams.topMargin);
        }

        return true;
    }
}

Answer 1

您应该使用拖动的距离而不是屏幕上的坐标。

layoutParams.leftMargin = layoutParams.leftMargin + deltaX;
layoutParams.topMargin = layoutParams.leftMargin + deltaY;

您可以从 Android 开发者网站获得完整的解决方案 https://developer.android.com/training/gestures/scale.html#drag
您将不得不根据您的需要对其进行调整。我稍微调整了一下。

// The ‘active pointer’ is the one currently moving our object.
private int mActivePointerId = INVALID_POINTER_ID;

@Override
public boolean onTouchEvent(MotionEvent ev) {
    // Let the ScaleGestureDetector inspect all events.
    mScaleDetector.onTouchEvent(ev);

    final int action = MotionEventCompat.getActionMasked(ev);

    switch (action) {
        case MotionEvent.ACTION_DOWN: {
            final int pointerIndex = MotionEventCompat.getActionIndex(ev);
            final float x = MotionEventCompat.getX(ev, pointerIndex);
            final float y = MotionEventCompat.getY(ev, pointerIndex);

            // Remember where we started (for dragging)
            mLastTouchX = x;
            mLastTouchY = y;
            // Save the ID of this pointer (for dragging)
            mActivePointerId = MotionEventCompat.getPointerId(ev, 0);
            break;
        }
        case MotionEvent.ACTION_MOVE: {
            // Find the index of the active pointer and fetch its position
            final int pointerIndex =
                    MotionEventCompat.findPointerIndex(ev, mActivePointerId);

            final float x = MotionEventCompat.getX(ev, pointerIndex);
            final float y = MotionEventCompat.getY(ev, pointerIndex);

            // Calculate the distance moved
            final float dx = x - mLastTouchX;
            final float dy = y - mLastTouchY;

            layoutParams.leftMargin += dx;
            layoutParams.topMargin += dy;
            tvText.setLayoutParams(layoutParams);
            lyRoot.invalidate();

            // Remember this touch position for the next move event
            mLastTouchX = x;
            mLastTouchY = y;
            break;
        }
        case MotionEvent.ACTION_UP: {
            mActivePointerId = INVALID_POINTER_ID;
            break;
        }
        case MotionEvent.ACTION_CANCEL: {
            mActivePointerId = INVALID_POINTER_ID;
            break;
        }
        case MotionEvent.ACTION_POINTER_UP: {
            final int pointerIndex = MotionEventCompat.getActionIndex(ev);
            final int pointerId = MotionEventCompat.getPointerId(ev, pointerIndex);

            if (pointerId == mActivePointerId) {
                // This was our active pointer going up. Choose a new
                // active pointer and adjust accordingly.
                final int newPointerIndex = pointerIndex == 0 ? 1 : 0;
                mLastTouchX = MotionEventCompat.getX(ev, newPointerIndex);
                mLastTouchY = MotionEventCompat.getY(ev, newPointerIndex);
                mActivePointerId = MotionEventCompat.getPointerId(ev, newPointerIndex);
            }
            break;
        }
    }
    return true;
}