先看一下效果圖
實現原理：根據手勢移動的距離動態設置控件的MarginLeft和MarginTop值。 廢話不多說，直接看代碼 java代碼
package com.example.wem.circledemo;import android.app.Activity;import android.os.Bundle;import android.util.DisplayMetrics;import android.view.Display;import android.view.MotionEvent;import android.view.View;import android.view.WindowManager;import android.widget.ImageView;import android.widget.RelativeLayout;import java.lang.reflect.Field;public class MainActivity extends Activity implements View.OnTouchListener { PRivate static final String TAG = MainActivity.class.getSimpleName(); private int startX = 0; private int startY = 0; private ImageView mImageView; private int mTop; private int mLeft; private int mMeasuredWidth; private int mMeasuredHeight; @Override protected void onCreate(Bundle savedInstanceState) { super.onCreate(savedInstanceState); setContentView(R.layout.activity_main); mImageView = (ImageView) findViewById(R.id.twitter_imageview); int w = View.MeasureSpec.makeMeasureSpec(0, View.MeasureSpec.UNSPECIFIED); int h = View.MeasureSpec.makeMeasureSpec(0, View.MeasureSpec.UNSPECIFIED); mImageView.measure(w, h);//測量控件的寬高 mMeasuredWidth = mImageView.getMeasuredWidth(); mMeasuredHeight = mImageView.getMeasuredHeight(); mImageView.setOnTouchListener(this); mTop = getScreenHeight() - dip2px(100); mLeft = (getScreenWidth() / 2) - (mMeasuredWidth / 2); setImageViewMargin(0, 0); //初始化控件據底部100dp 居中顯示 } @Override public boolean onTouch(View v, MotionEvent event) { switch (event.getAction()) { case MotionEvent.ACTION_DOWN: //初始化開始位置 startX = (int) event.getRawX(); startY = (int) event.getRawY(); mTop = mImageView.getTop(); mLeft = mImageView.getLeft(); break; case MotionEvent.ACTION_MOVE: //手勢移動的dX和dY為控件的marginLeft和marginTop int moveX = (int) event.getRawX(); int moveY = (int) event.getRawY(); int dX = moveX - startX; int dY = moveY - startY; setImageViewMargin(dX, dY); break; case MotionEvent.ACTION_UP: //初始值重置 startX = (int) event.getRawX(); startY = (int) event.getRawY(); mTop = mImageView.getTop(); mLeft = mImageView.getLeft(); break; } return true; } /** * 動態設置控件的marginTop 和 marginLeft的值 * * @param dX x軸的偏移量 * @param dY y軸的偏移量 */ private void setImageViewMargin(int dX, int dY) { RelativeLayout.LayoutParams layoutParams = (RelativeLayout.LayoutParams) mImageView.getLayoutParams(); int top = mTop + dY; int left = mLeft + dX; int l = getScreenWidth() - mMeasuredWidth; int t = getScreenHeight() - mMeasuredHeight - getStatusBarHeight(); //設置left和top的邊界值 if (left < 0) { left = 0; } else if (left > l) { left = l; } if (top < 0) { top = 0; } else if (top > t) { top = t; } layoutParams.topMargin = top; layoutParams.leftMargin = left; mImageView.setLayoutParams(layoutParams); } /** * 獲取狀態欄的高度 * * @return */ private int getStatusBarHeight() { Class<?> c = null; Object obj = null; Field field = null; int x = 0, sbar = 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()); sbar = getResources().getDimensionPixelSize(x); } catch (Exception e1) { e1.printStackTrace(); } return sbar; } /** * 獲取屏幕的寬度 * * @return */ private int getScreenWidth() { WindowManager windowManager = getWindowManager(); Display defaultDisplay = windowManager.getDefaultDisplay(); return defaultDisplay.getWidth(); } /** * 獲取屏幕的高度 * * @return */ private int getScreenHeight() { WindowManager windowManager = getWindowManager(); Display defaultDisplay = windowManager.getDefaultDisplay(); return defaultDisplay.getHeight(); } /** * dp轉px * * @param dp * @return */ private int dip2px(int dp) { DisplayMetrics displayMetrics = getResources().getDisplayMetrics(); float density = displayMetrics.density; return (int) (dp * density + 0.5); } /** * px轉dp * * @param px * @return */ private int px2dip(int px) { float density = getResources().getDisplayMetrics().density; return (int) (px / density + 0.5); }}xml代碼就一個ImageView
<?xml version="1.0" encoding="utf-8"?><RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android" xmlns:tools="http://schemas.android.com/tools" android:id="@+id/activity_main" android:layout_width="match_parent" android:layout_height="match_parent" > <ImageView android:id="@+id/twitter_imageview" android:layout_width="wrap_content" android:layout_height="wrap_content" android:src="@mipmap/twitter_icon" /></RelativeLayout>當控件的寬（layout_width）和高（layout_height）設置為wrap_content時，mImageView.getMeasuredWidth();和mImageView.getWidth();的值是相等的。否者反之。
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