Android实现随意拖动View效果

项目过程中需要实现View能在页面中随意的拖动，刚开始实现是用悬浮球的形式进行实现，因为之前项目中用过，实现后发现用户每次安装后，都有权限的限制，甚至有些用户关闭悬浮球权限之后，不知道怎么在手机上打开悬浮球的权限，这样的话用户体验很不好，所以自己重新自定义实现在页面中拖动，不需要请求权限。

1、先来看看效果图：

111.gif

2、自定义随意拖动View：

package com.dragdemo;

import android.annotation.SuppressLint;
import android.content.Context;
import android.util.AttributeSet;
import android.util.Log;
import android.view.MotionEvent;
import android.widget.ImageView;

/**
 * 随意拖动的view
 */
@SuppressLint("AppCompatCustomView")
public class DragView extends ImageView {
    private int width;
    private int height;
    private int screenWidth;
    private int screenHeight;
    private Context context;
    //是否拖动
    private boolean isDrag = false;

    public boolean isDrag() {
        return isDrag;
    }

    public DragView(Context context, AttributeSet attrs) {
        super(context, attrs);
        this.context = context;
    }

    @Override
    protected void onMeasure(int widthMeasureSpec, int heightMeasureSpec) {
        super.onMeasure(widthMeasureSpec, heightMeasureSpec);
        width = getMeasuredWidth();
        height = getMeasuredHeight();
        screenWidth = ScreenUtil.getScreenWidth(context);
        screenHeight = ScreenUtil.getScreenHeight(context) - getStatusBarHeight();
    }

    public int getStatusBarHeight() {
        int resourceId = getResources().getIdentifier("status_bar_height", "dimen", "android");
        return getResources().getDimensionPixelSize(resourceId);
    }

    private float downX;
    private float downY;

    @Override
    public boolean onTouchEvent(MotionEvent event) {
        super.onTouchEvent(event);
        if (this.isEnabled()) {
            switch (event.getAction()) {
                case MotionEvent.ACTION_DOWN:
                    isDrag = false;
                    downX = event.getX();
                    downY = event.getY();
                    break;
                case MotionEvent.ACTION_MOVE:
                    Log.e("kid", "ACTION_MOVE");
                    final float xDistance = event.getX() - downX;
                    final float yDistance = event.getY() - downY;
                    int l, r, t, b;
                    //当水平或者垂直滑动距离大于10,才算拖动事件
                    if (Math.abs(xDistance) > 10 || Math.abs(yDistance) > 10) {
                        Log.e("kid", "Drag");
                        isDrag = true;
                        l = (int) (getLeft() + xDistance);
                        r = l + width;
                        t = (int) (getTop() + yDistance);
                        b = t + height;
                        //不划出边界判断,此处应按照项目实际情况,因为本项目需求移动的位置是手机全屏,
                        // 所以才能这么写,如果是固定区域,要得到父控件的宽高位置后再做处理
                        if (l < 0) {
                            l = 0;
                            r = l + width;
                        } else if (r > screenWidth) {
                            r = screenWidth;
                            l = r - width;
                        }
                        if (t < 0) {
                            t = 0;
                            b = t + height;
                        } else if (b > screenHeight) {
                            b = screenHeight;
                            t = b - height;
                        }
                        this.layout(l, t, r, b);
                    }
                    break;
                case MotionEvent.ACTION_UP:
                    setPressed(false);
                    break;
                case MotionEvent.ACTION_CANCEL:
                    setPressed(false);
                    break;
            }
            return true;
        }
        return false;
    }
}

3、用到的工具类：

package com.dragdemo;

import android.content.Context;
import android.util.DisplayMetrics;
import android.view.Display;
import android.view.View;
import android.view.WindowManager;

public class ScreenUtil {
    private static int width = 0;
    private static int height = 0;
    private static int showHeight = 0;
    private static int statusHeight = 0;
    private static float density = 0;

    public static int getScreenWidth(Context context) {
        if (width == 0) {
            WindowManager manager = (WindowManager) context
                    .getSystemService(Context.WINDOW_SERVICE);
            Display display = manager.getDefaultDisplay();
            width = display.getWidth();
        }
        return width;
    }

    public static int getScreenHeight(Context context) {
        if (height == 0) {
            WindowManager manager = (WindowManager) context
                    .getSystemService(Context.WINDOW_SERVICE);
            Display display = manager.getDefaultDisplay();
            height = display.getHeight();
        }
        return height;
    }

    public static int getScreenShowHeight(Context context) {
        if (showHeight == 0) {
            showHeight = getScreenHeight(context) - getStatusBarHeight(context);
        }
        return showHeight;
    }

    public static int getStatusBarHeight(Context context) {
        if (statusHeight > 0) {
            return statusHeight;
        }
        Class<?> c = null;
        Object obj = null;
        java.lang.reflect.Field field = null;
        int x = 0;
        try {
            c = Class.forName("com.android.internal.R$dimen");
            obj = c.newInstance();
            field = c.getField("status_bar_height");
            x = Integer.parseInt(field.get(obj).toString());
            statusHeight = context.getResources().getDimensionPixelSize(x);
            return statusHeight;
        } catch (Throwable e) {
            e.printStackTrace();
        }
        return statusHeight;
    }

    public static float getScreenDensity(Context context) {
        if (density == 0) {
            try {
                DisplayMetrics dm = new DisplayMetrics();
                WindowManager manager = (WindowManager) context
                        .getSystemService(Context.WINDOW_SERVICE);
                manager.getDefaultDisplay().getMetrics(dm);
                density = dm.density;
            } catch (Exception ex) {
                ex.printStackTrace();
                density = 1.0f;
            }
        }
        return density;
    }

    public static float getScreentMinLength(Context context) {
        return getScreenHeight(context) > getScreenWidth(context) ? getScreenWidth(context)
                : getScreenHeight(context);
    }

    /**
     * 根据指定k的系数获取屏幕在max范围内的最大长宽,默认宽比较小
     *
     * @param context
     * @param k
     * @return
     */
    public static DrawWrap getCutWrap(Context context, float k, float max) {
        float tWidth = getScreenWidth(context);
        float tHeight = getScreenHeight(context);
        if (tWidth * max * k > tHeight) {
            return new DrawWrap(tHeight * max / k, tHeight * max);
        } else {
            return new DrawWrap(tWidth * max, tWidth * max * k);
        }
    }

    public static class DrawWrap {
        public float width;
        public float height;

        public DrawWrap(float width, float height) {
            this.width = width;
            this.height = height;
        }
    }

    public static int dip2px(Context context, float dipValue) {
        return (int) (dipValue * getScreenDensity(context) + 0.5f);
    }

    /**
     * 将sp值转换为px值，保证文字大小不变
     *
     * @param context
     * @param spValue （DisplayMetrics类中属性scaledDensity）
     * @return
     */
    public static int sp2px(Context context, float spValue) {
        final float fontScale = context.getResources().getDisplayMetrics().scaledDensity;
        return (int) (spValue * fontScale + 0.5f);
    }

    /**
     * 根据手机的分辨率从 px(像素) 的单位 转成为 dp
     */
    public static int px2dip(Context context, float pxValue) {
        final float scale = context.getResources().getDisplayMetrics().density;
        return (int) (pxValue / scale + 0.5f);
    }

    /**
     * 获取屏幕中控件顶部位置的高度--即控件顶部的Y点
     *
     * @return
     */
    public static int getScreenViewTopHeight(View view) {
        return view.getTop();
    }

    /**
     * 获取屏幕中控件底部位置的高度--即控件底部的Y点
     *
     * @return
     */
    public static int getScreenViewBottomHeight(View view) {
        return view.getBottom();
    }

    /**
     * 获取屏幕中控件左侧的位置--即控件左侧的X点
     *
     * @return
     */
    public static int getScreenViewLeftHeight(View view) {
        return view.getLeft();
    }

    /**
     * 获取屏幕中控件右侧的位置--即控件右侧的X点
     *
     * @return
     */
    public static int getScreenViewRightHeight(View view) {
        return view.getRight();
    }

    /*
     * 获取控件宽
     */
    public static int getWidth(View view) {
        int w = View.MeasureSpec.makeMeasureSpec(0,
                View.MeasureSpec.UNSPECIFIED);
        int h = View.MeasureSpec.makeMeasureSpec(0,
                View.MeasureSpec.UNSPECIFIED);
        view.measure(w, h);
        return (view.getMeasuredWidth());
    }

    /*
     * 获取控件高
     */
    public static int getHeight(View view) {
        int w = View.MeasureSpec.makeMeasureSpec(0,
                View.MeasureSpec.UNSPECIFIED);
        int h = View.MeasureSpec.makeMeasureSpec(0,
                View.MeasureSpec.UNSPECIFIED);
        view.measure(w, h);
        return (view.getMeasuredHeight());
    }
}

4、XML文件：

<com.dragdemo.DragView
        android:id="@+id/iv_drag"
        android:layout_width="80dp"
        android:layout_height="80dp"
        android:layout_gravity="center"
        android:src="@drawable/ic_launcher_background" />

5、MainActivity代码逻辑

package com.dragdemo;

import android.support.v7.app.AppCompatActivity;
import android.os.Bundle;
import android.view.View;
import android.widget.Toast;

public class MainActivity extends AppCompatActivity {

    DragView iv_drag;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        iv_drag = (DragView) findViewById(R.id.iv_drag);
        iv_drag.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                if (!iv_drag.isDrag()) {
                    Toast.makeText(MainActivity.this, "响应点击", Toast.LENGTH_SHORT).show();
                }
            }
        });
    }
}