我正在尝试在Android应用中实施拖动。我正在关注here列出的Android文档示例。这是代码：
// The current viewport. This rectangle represents the currently visible
// chart domain and range.
private RectF mCurrentViewport =
new RectF(AXIS_X_MIN, AXIS_Y_MIN, AXIS_X_MAX, AXIS_Y_MAX);
// The current destination rectangle (in pixel coordinates) into which the
// chart data should be drawn.
private Rect mContentRect;
private final GestureDetector.SimpleOnGestureListener mGestureListener
= new GestureDetector.SimpleOnGestureListener() {
...
@Override
public boolean onScroll(MotionEvent e1, MotionEvent e2,
float distanceX, float distanceY) {
// Scrolling uses math based on the viewport (as opposed to math using pixels).
// Pixel offset is the offset in screen pixels, while viewport offset is the
// offset within the current viewport.
float viewportOffsetX = distanceX * mCurrentViewport.width()
/ mContentRect.width();
float viewportOffsetY = -distanceY * mCurrentViewport.height()
/ mContentRect.height();
...
// Updates the viewport, refreshes the display.
setViewportBottomLeft(
mCurrentViewport.left + viewportOffsetX,
mCurrentViewport.bottom + viewportOffsetY);
...
return true;
}
在执行onScroll方法之后，如何更新视图？该示例中仅更新了mCurrentViewport变量。
答案 0 :(得分：1)
使用这些Android教程有很多代码未在其中提及。我建议使用Android Studio菜单中的导入示例。这可能是您需要玩的东西：
https://github.com/googlesamples/android-BasicGestureDetect/
如果您使用上面的guthyb代码，则我将下面的Android教程代码嵌入了BasicGestureDetectFragment.java中。在“ moveLog”方法中，您可以使用dx值执行任何操作。我还在下面放置了一个代码，该代码向您展示如何创建一个拖动图片的应用程序。只需将“ ic_launcher.png”添加到res文件夹下的图像文件夹，即可获得图像并移动它。我建议使用比Android简单得多的Corona SDK进行编码。
/*
* Copyright (C) 2013 The Android Open Source Project
*
* Licensed under the Apache License, Version 2.0 (the "License");
* you may not use this file except in compliance with the License.
* You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*/
package com.example.android.basicgesturedetect;
import android.content.Intent;
import android.os.Bundle;
import android.support.v4.app.Fragment;
import android.support.v4.view.MotionEventCompat;
import android.view.GestureDetector;
import android.view.MenuItem;
import android.view.MotionEvent;
import android.view.View;
import com.example.android.common.logger.Log;
import com.example.android.common.logger.LogFragment;
import static android.view.MotionEvent.INVALID_POINTER_ID;
public class BasicGestureDetectFragment extends Fragment{
private int mActivePointerId = INVALID_POINTER_ID;
@Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setHasOptionsMenu(true);
}
@Override
public void onActivityCreated(Bundle savedInstanceState) {
super.onActivityCreated(savedInstanceState);
View gestureView = getActivity().findViewById(R.id.sample_output);
gestureView.setFocusable(true);
// BEGIN_INCLUDE(init_detector)
// First create the GestureListener that will include all our callbacks.
// Then create the GestureDetector, which takes that listener as an argument.
GestureDetector.SimpleOnGestureListener gestureListener = new GestureListener();
final GestureDetector gd = new GestureDetector(getActivity(), gestureListener);
/* For the view where gestures will occur, create an onTouchListener that sends
* all motion events to the gesture detector. When the gesture detector
* actually detects an event, it will use the callbacks you created in the
* SimpleOnGestureListener to alert your application.
*/
gestureView.setOnTouchListener(new View.OnTouchListener() {
float mLastTouchX;
float mLastTouchY;
float mPosX;
float mPosY;
@Override
public boolean onTouch(View view, MotionEvent motionEvent) {
gd.onTouchEvent(motionEvent);
//**********
final int action = MotionEventCompat.getActionMasked(motionEvent);
switch (action) {
case MotionEvent.ACTION_DOWN: {
final int pointerIndex = MotionEventCompat.getActionIndex(motionEvent);
final float x = MotionEventCompat.getX(motionEvent, pointerIndex);
final float y = MotionEventCompat.getY(motionEvent, pointerIndex);
// Remember where we started (for dragging)
mLastTouchX = x;
mLastTouchY = y;
// Save the ID of this pointer (for dragging)
mActivePointerId = MotionEventCompat.getPointerId(motionEvent, 0);
break;
}
case MotionEvent.ACTION_MOVE: {
// Find the index of the active pointer and fetch its position
final int pointerIndex =
MotionEventCompat.findPointerIndex(motionEvent, mActivePointerId);
final float x = MotionEventCompat.getX(motionEvent, pointerIndex);
final float y = MotionEventCompat.getY(motionEvent, pointerIndex);
// Calculate the distance moved
final float dx = x - mLastTouchX;
final float dy = y - mLastTouchY;
mPosX += dx;
mPosY += dy;
moveLog(dx);
//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(motionEvent);
final int pointerId = MotionEventCompat.getPointerId(motionEvent, 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(motionEvent, newPointerIndex);
mLastTouchY = MotionEventCompat.getY(motionEvent, newPointerIndex);
mActivePointerId = MotionEventCompat.getPointerId(motionEvent, newPointerIndex);
}
break;
}
}
//**********
return false;
}
});
// END_INCLUDE(init_detector)
}
@Override
public boolean onOptionsItemSelected(MenuItem item) {
if (item.getItemId() == R.id.sample_action) {
clearLog();
}
return true;
}
public void clearLog() {
LogFragment logFragment = ((LogFragment) getActivity().getSupportFragmentManager()
.findFragmentById(R.id.log_fragment));
logFragment.getLogView().setText("");
}
public void moveLog(float x) {
//do whatever you like
}
}
只需在Android Studio下启动空白应用程序： 1-将activity_main.xml更改为此：
<?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/main"
android:layout_width="match_parent"
android:layout_height="match_parent" >
<ImageView
android:id="@+id/image"
android:layout_width="150dp"
android:layout_height="150dp"
android:layout_alignParentLeft="true"
android:layout_alignParentTop="true"
android:contentDescription="@string/app_name"
android:src="@drawable/ic_launcher" />
</RelativeLayout>
和MainActivity.java。 （将包名称保留为您自己的：包com.jorc.move.myapplication;）
package com.jorc.move.myapplication;
import android.annotation.SuppressLint;
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.ImageView;
import android.widget.RelativeLayout;
import android.widget.Toast;
public class MainActivity extends AppCompatActivity {
private ViewGroup mainLayout;
private ImageView image;
private int xDelta;
private int yDelta;
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
mainLayout = (RelativeLayout) findViewById(R.id.main);
image = (ImageView) findViewById(R.id.image);
image.setOnTouchListener(onTouchListener());
}
private View.OnTouchListener onTouchListener() {
return new View.OnTouchListener() {
@SuppressLint("ClickableViewAccessibility")
@Override
public boolean onTouch(View view, MotionEvent event) {
final int x = (int) event.getRawX();
final int y = (int) event.getRawY();
switch (event.getAction() & MotionEvent.ACTION_MASK) {
case MotionEvent.ACTION_DOWN:
RelativeLayout.LayoutParams lParams = (RelativeLayout.LayoutParams)
view.getLayoutParams();
xDelta = x - lParams.leftMargin;
yDelta = y - lParams.topMargin;
break;
case MotionEvent.ACTION_UP:
Toast.makeText(MainActivity.this,
"thanks for new location!", Toast.LENGTH_SHORT)
.show();
break;
case MotionEvent.ACTION_MOVE:
RelativeLayout.LayoutParams layoutParams = (RelativeLayout.LayoutParams) view
.getLayoutParams();
layoutParams.leftMargin = x - xDelta;
layoutParams.topMargin = y - yDelta;
layoutParams.rightMargin = 0;
layoutParams.bottomMargin = 0;
view.setLayoutParams(layoutParams);
break;
}
mainLayout.invalidate();
return true;
}
};
}
}