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在android中做一个竖着的seekbar效果

时间：2024-3-2 19:47     作者：韩俊     分类： Android

工作繁忙，总想有机会停下来喘口气，整理一下思路，做一些积累，但是这样的机会很少。要做android的界面，基础的要求是熟悉那些内置的组件（prebuilt componments），而有时候这些组件是不够用的，这时候我们就需要自己写一个新的，或者修改内置的。这就要求我们了解更多知识，比如各个View是怎么画出来的，UI上各种事件是如何分发和处理的等等。这些我都计划写出来和大家分享，网络上中文资料，说得清楚的太少了，就那么几篇被广泛的转载。今天说一说如何做一个vertical seekbar，竖起来的seekbar。实现它的过程中就会涉及一些View是如何被画出来的知识。通过本文你可以实现一个verticalseekbar，你也可以学到一些使用seekbar的知识。

我的一个同事很牛，需要自定义的组件时，从framework中抠出来相关（功能相似、在继承关系的hierarchy中地位相当）的代码（类），在自己的应用程序中做修改，实现自己想要的功能。需要的style、drawable等资源，有些是在应用程序里用不了的，就也自己做一份。我们公司做整个系统，从硬件到android到android上的应用系统， framework我们也修改，主要是功能上的增减。在framework里增加一个verticalseekbar我们也能做到，但是这样兼容性就被破坏了，所以这位仁兄把需要的拿出来在自己的程序中实现。

我做vertical seekbar也采取这个策略，不和大家啰嗦实现过程中太多因果逻辑，我想很多读者读这篇文章就是为了做出来一个vertical seekbar。为了方便手头没有代码和开发环境的读者，我会贴上framework中的相关代码。

vertical seekbar当然要实现seekbar一样的功能，所以首先seekbar有的vertical seekbar都要有，直接在你的工程中新建一个类vertical seekbar，从framework中把seekbar的代码复制过来，做一些必要的修改。我们来看看seekbar做了些什么.

seekbar代码：

[java] view
plaincopy

/*

  • Copyright (C) 2006 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 android.widget;
    import android.content.Context;
    import android.util.AttributeSet;
    /**
  • A SeekBar is an extension of ProgressBar that adds a draggable thumb. The user can touch
  • the thumb and drag left or right to set the current progress level or use the arrow keys.
  • Placing focusable widgets to the left or right of a SeekBar is discouraged.
  • <p>
  • Clients of the SeekBar can attach a {@link SeekBar.OnSeekBarChangeListener} to
  • be notified of the user's actions.

  • @attr ref android.R.styleable#SeekBar_thumb
    */
    public class SeekBar extends AbsSeekBar {
    /**

    • A callback that notifies clients when the progress level has been
    • changed. This includes changes that were initiated by the user through a
    • touch gesture or arrow key/trackball as well as changes that were initiated

    • programmatically.
      */
      public interface OnSeekBarChangeListener {

      /**

      • Notification that the progress level has changed. Clients can use the fromUser parameter
      • to distinguish user-initiated changes from those that occurred programmatically.
      • @param seekBar The SeekBar whose progress has changed
      • @param progress The current progress level. This will be in the range 0..max where max
      • was set by {@link ProgressBar#setMax(int)}. (The default value for max is 100.)
      • @param fromUser True if the progress change was initiated by the user.
        */
        void onProgressChanged(SeekBar seekBar, int progress, boolean fromUser);

      /**

      • Notification that the user has started a touch gesture. Clients may want to use this
      • to disable advancing the seekbar.
      • @param seekBar The SeekBar in which the touch gesture began
        */
        void onStartTrackingTouch(SeekBar seekBar);

      /**

      • Notification that the user has finished a touch gesture. Clients may want to use this
      • to re-enable advancing the seekbar.
      • @param seekBar The SeekBar in which the touch gesture began
        */
        void onStopTrackingTouch(SeekBar seekBar);
        }
        private OnSeekBarChangeListener mOnSeekBarChangeListener;

    public SeekBar(Context context) {
    this(context, null);
    }

    public SeekBar(Context context, AttributeSet attrs) {
    this(context, attrs, com.android.internal.R.attr.seekBarStyle);
    }
    public SeekBar(Context context, AttributeSet attrs, int defStyle) {
    super(context, attrs, defStyle);
    }
    @Override
    void onProgressRefresh(float scale, boolean fromUser) {
    super.onProgressRefresh(scale, fromUser);
    if (mOnSeekBarChangeListener != null) {
    mOnSeekBarChangeListener.onProgressChanged(this, getProgress(), fromUser);
    }
    }
    /**

    • Sets a listener to receive notifications of changes to the SeekBar's progress level. Also
    • provides notifications of when the user starts and stops a touch gesture within the SeekBar.
    • @param l The seek bar notification listener
    • @see SeekBar.OnSeekBarChangeListener
      */
      public void setOnSeekBarChangeListener(OnSeekBarChangeListener l) {
      mOnSeekBarChangeListener = l;
      }

    @Override
    void onStartTrackingTouch() {
    if (mOnSeekBarChangeListener != null) {
    mOnSeekBarChangeListener.onStartTrackingTouch(this);
    }
    }

    @Override
    void onStopTrackingTouch() {
    if (mOnSeekBarChangeListener != null) {
    mOnSeekBarChangeListener.onStopTrackingTouch(this);
    }
    }

}

它定义了一个接口OnSeekBarChangeListener，接口中定义了三个方法：

void onProgressChanged(SeekBar seekBar, int progress, boolean fromUser);
void onStartTrackingTouch(SeekBar seekBar);
void onStopTrackingTouch(SeekBar seekBar);

看名字也知道它们是做什么的，代码也给了注释。那么它们是怎么做到的呢？seekbar中声明了一个该接口的对象mOnSeekBarChangeListener，方法setOnSeekBarChangeListener()将给它赋值。在你的程序中定义一个对象，实现OnSeekBarChangeListener，并调用setOnSeekBarChangeListener()把这个对象传给mOnSeekBarChangeListener。在seekbar中还有几个override的方法：

void onProgressRefresh(float scale, boolean fromUser)

void onStartTrackingTouch()
void onStopTrackingTouch()

这些方法会在发生了相应事件的时候被调用，而它们又相应地去调用mOnSeekBarChangeListener中的方法，于是你的程序的定义的响应各种事件的方法就被执行了。

但是这些还不够，我们要让seekbar竖起来，要让thumb上下滑动，实现这些特性的代码在什么地方呢？我们顺着seekbar的继承关系向上找。来看看absseekbar。

absseekbar的代码：

[java] view
plaincopy

/*

  • Copyright (C) 2007 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 android.widget;
    import android.content.Context;
    import android.content.res.TypedArray;
    import android.graphics.Canvas;
    import android.graphics.Rect;
    import android.graphics.drawable.Drawable;
    import android.util.AttributeSet;
    import android.view.KeyEvent;
    import android.view.MotionEvent;
    public abstract class AbsSeekBar extends ProgressBar {
    private Drawable mThumb;
    private int mThumbOffset;

    /**

    • On touch, this offset plus the scaled value from the position of the
    • touch will form the progress value. Usually 0.
      */
      float mTouchProgressOffset;
      /**
    • Whether this is user seekable.
      */
      boolean mIsUserSeekable = true;
      /**
    • On key presses (right or left), the amount to increment/decrement the
    • progress.
      */
      private int mKeyProgressIncrement = 1;

    private static final int NO_ALPHA = 0xFF;
    private float mDisabledAlpha;

    public AbsSeekBar(Context context) {
    super(context);
    }
    public AbsSeekBar(Context context, AttributeSet attrs) {
    super(context, attrs);
    }
    public AbsSeekBar(Context context, AttributeSet attrs, int defStyle) {
    super(context, attrs, defStyle);
    TypedArray a = context.obtainStyledAttributes(attrs,
    com.android.internal.R.styleable.SeekBar, defStyle, 0);
    Drawable thumb = a.getDrawable(com.android.internal.R.styleable.SeekBar_thumb);
    setThumb(thumb);
    int thumbOffset =
    a.getDimensionPixelOffset(com.android.internal.R.styleable.SeekBar_thumbOffset, 0);
    setThumbOffset(thumbOffset);
    a.recycle();
    a = context.obtainStyledAttributes(attrs,
    com.android.internal.R.styleable.Theme, 0, 0);
    mDisabledAlpha = a.getFloat(com.android.internal.R.styleable.Theme_disabledAlpha, 0.5f);
    a.recycle();
    }
    /**

    • Sets the thumb that will be drawn at the end of the progress meter within the SeekBar
    • @param thumb Drawable representing the thumb
      */
      public void setThumb(Drawable thumb) {
      if (thumb != null) {
      thumb.setCallback(this);
      }
      mThumb = thumb;
      invalidate();
      }
      /**
    • @see #setThumbOffset(int)
      */
      public int getThumbOffset() {
      return mThumbOffset;
      }
      /**
    • Sets the thumb offset that allows the thumb to extend out of the range of
    • the track.
    • @param thumbOffset The offset amount in pixels.
      */
      public void setThumbOffset(int thumbOffset) {
      mThumbOffset = thumbOffset;
      invalidate();
      }
      /**
    • Sets the amount of progress changed via the arrow keys.
    • @param increment The amount to increment or decrement when the user
    • presses the arrow keys.
      */
      public void setKeyProgressIncrement(int increment) {
      mKeyProgressIncrement = increment < 0 ? -increment : increment;
      }
      /**
    • Returns the amount of progress changed via the arrow keys.
    • <p>
    • By default, this will be a value that is derived from the max progress.
    • @return The amount to increment or decrement when the user presses the
    • arrow keys. This will be positive.
      */
      public int getKeyProgressIncrement() {
      return mKeyProgressIncrement;
      }

    @Override
    public synchronized void setMax(int max) {
    super.setMax(max);
    if ((mKeyProgressIncrement == 0) || (getMax() / mKeyProgressIncrement > 20)) {
    // It will take the user too long to change this via keys, change it
    // to something more reasonable
    setKeyProgressIncrement(Math.max(1, Math.round((float) getMax() / 20)));
    }
    }
    @Override
    protected boolean verifyDrawable(Drawable who) {
    return who == mThumb || super.verifyDrawable(who);
    }
    @Override
    protected void drawableStateChanged() {
    super.drawableStateChanged(); 

    Drawable progressDrawable = getProgressDrawable();  
if (progressDrawable != null) {  
    progressDrawable.setAlpha(isEnabled() ? NO_ALPHA : (int) (NO_ALPHA * mDisabledAlpha));  
}  

if (mThumb != null &amp;&amp; mThumb.isStateful()) {  
    int[] state = getDrawableState();  
    mThumb.setState(state);  
}

    }

    @Override
    void onProgressRefresh(float scale, boolean fromUser) {
    Drawable thumb = mThumb;
    if (thumb != null) {
    setThumbPos(getWidth(), thumb, scale, Integer.MIN_VALUE);
    /*

    • Since we draw translated, the drawable's bounds that it signals
    • for invalidation won't be the actual bounds we want invalidated,
    • so just invalidate this whole view.
      */
      invalidate();
      }
      }

    @Override
    protected void onSizeChanged(int w, int h, int oldw, int oldh) {
    Drawable d = getCurrentDrawable();
    Drawable thumb = mThumb;
    int thumbHeight = thumb == null ? 0 : thumb.getIntrinsicHeight();
    // The max height does not incorporate padding, whereas the height
    // parameter does
    int trackHeight = Math.min(mMaxHeight, h - mPaddingTop - mPaddingBottom); 

    int max = getMax();  
float scale = max &gt; 0 ? (float) getProgress() / (float) max : 0;  

if (thumbHeight &gt; trackHeight) {  
    if (thumb != null) {  
        setThumbPos(w, thumb, scale, 0);  
    }  
    int gapForCenteringTrack = (thumbHeight - trackHeight) / 2;  
    if (d != null) {  
        // Canvas will be translated by the padding, so 0,0 is where we start drawing  
        d.setBounds(0, gapForCenteringTrack,   
                w - mPaddingRight - mPaddingLeft, h - mPaddingBottom - gapForCenteringTrack  
                - mPaddingTop);  
    }  
} else {  
    if (d != null) {  
        // Canvas will be translated by the padding, so 0,0 is where we start drawing  
        d.setBounds(0, 0, w - mPaddingRight - mPaddingLeft, h - mPaddingBottom  
                - mPaddingTop);  
    }  
    int gap = (trackHeight - thumbHeight) / 2;  
    if (thumb != null) {  
        setThumbPos(w, thumb, scale, gap);  
    }  
}

    }
    /**

    • @param gap If set to {@link Integer#MIN_VALUE}, this will be ignored and
      /
      private void setThumbPos(int w, Drawable thumb, float scale, int gap) {
      int available = w - mPaddingLeft - mPaddingRight;
      int thumbWidth = thumb.getIntrinsicWidth();
      int thumbHeight = thumb.getIntrinsicHeight();
      available -= thumbWidth;
      // The extra space for the thumb to move on the track
      available += mThumbOffset       2;
      int thumbPos = (int) (scale * available);
      int topBound, bottomBound;
      if (gap == Integer.MIN_VALUE) {
      Rect oldBounds = thumb.getBounds();
      topBound = oldBounds.top;
      bottomBound = oldBounds.bottom;
      } else {
      topBound = gap;
      bottomBound = gap + thumbHeight;
      }

      // Canvas will be translated, so 0,0 is where we start drawing
      thumb.setBounds(thumbPos, topBound, thumbPos + thumbWidth, bottomBound);
      }

    @Override
    protected synchronized void onDraw(Canvas canvas) {
    super.onDraw(canvas);
    if (mThumb != null) {
    canvas.save();
    // Translate the padding. For the x, we need to allow the thumb to
    // draw in its extra space
    canvas.translate(mPaddingLeft - mThumbOffset, mPaddingTop);
    mThumb.draw(canvas);
    canvas.restore();
    }
    }
    @Override
    protected synchronized void onMeasure(int widthMeasureSpec, int heightMeasureSpec) {
    Drawable d = getCurrentDrawable();
    int thumbHeight = mThumb == null ? 0 : mThumb.getIntrinsicHeight();
    int dw = 0;
    int dh = 0;
    if (d != null) {
    dw = Math.max(mMinWidth, Math.min(mMaxWidth, d.getIntrinsicWidth()));
    dh = Math.max(mMinHeight, Math.min(mMaxHeight, d.getIntrinsicHeight()));
    dh = Math.max(thumbHeight, dh);
    }
    dw += mPaddingLeft + mPaddingRight;
    dh += mPaddingTop + mPaddingBottom; 

    setMeasuredDimension(resolveSize(dw, widthMeasureSpec),  
        resolveSize(dh, heightMeasureSpec));

    }

    @Override
    public boolean onTouchEvent(MotionEvent event) {
    if (!mIsUserSeekable || !isEnabled()) {
    return false;
    } 

    switch (event.getAction()) {  
    case MotionEvent.ACTION_DOWN:  
        setPressed(true);  
        onStartTrackingTouch();  
        trackTouchEvent(event);  
        break;  

    case MotionEvent.ACTION_MOVE:  
        trackTouchEvent(event);  
        attemptClaimDrag();  
        break;  

    case MotionEvent.ACTION_UP:  
        trackTouchEvent(event);  
        onStopTrackingTouch();  
        setPressed(false);  
        break;  

    case MotionEvent.ACTION_CANCEL:  
        onStopTrackingTouch();  
        setPressed(false);  
        break;  
}  
return true;

    }
    private void trackTouchEvent(MotionEvent event) {
    final int width = getWidth();
    final int available = width - mPaddingLeft - mPaddingRight;
    int x = (int)event.getX();
    float scale;
    float progress = 0;
    if (x < mPaddingLeft) {
    scale = 0.0f;
    } else if (x > width - mPaddingRight) {
    scale = 1.0f;
    } else {
    scale = (float)(x - mPaddingLeft) / (float)available;
    progress = mTouchProgressOffset;
    } 

    final int max = getMax();  
progress &#43;= scale * max;  

setProgress((int) progress, true);

    }
    /**

    • Tries to claim the user's drag motion, and requests disallowing any
    • ancestors from stealing events in the drag.
      */
      private void attemptClaimDrag() {
      if (mParent != null) {
      mParent.requestDisallowInterceptTouchEvent(true);
      }
      }

    /**

    • This is called when the user has started touching this widget.
      */
      void onStartTrackingTouch() {
      }
      /**
    • This is called when the user either releases his touch or the touch is
    • canceled.
      */
      void onStopTrackingTouch() {
      }
      /**

    • Called when the user changes the seekbar's progress by using a key event.
      */
      void onKeyChange() {
      }
      @Override
      public boolean onKeyDown(int keyCode, KeyEvent event) {
      int progress = getProgress();

      switch (keyCode) {
      case KeyEvent.KEYCODE_DPAD_LEFT:
      if (progress <= 0) break;
      setProgress(progress - mKeyProgressIncrement, true);
      onKeyChange();
      return true; 

      case KeyEvent.KEYCODE_DPAD_RIGHT:  
    if (progress &gt;= getMax()) break;  
    setProgress(progress &#43; mKeyProgressIncrement, true);  
    onKeyChange();  
    return true;

      }
      return super.onKeyDown(keyCode, event);
      }
      }

连上注释372行，不多。我们看到有onTouchEvent()，trackTouchEvent()，onProgressRefresh()，setThumbPos()等一些方法，这些都是和seekbar功能相关的方法，去看看它们的注释。

onTouchEvent()是在View中就有定义的方法，（touch）事件处理我日后有空我会再发文章讨论，现在我们只要知道，在用户触摸seekbar（absseekbar）时，这个方法会响应touch事件就够了。onTouchEvent()会判断用户的动作，然后调用前述的一些方法（注意去看代码），注意它调用的顺序，判断是ACTION_DOWN时先调用onStartTrackingTouch()再调用trackTouchEvent(event)，于是在你的程序中定义的 onStartTrackingTouch()先执行了；判断是ACTION_UP时先调用trackTouchEvent(event)再调用onStopTrackingTouch()，至于为什么我就不啰嗦了，有时候这个顺序是很重要的。

trackTouchEvent()根据touch的位置来设置进度，它计算出progress后调用setProgress()，setProgress()是progressbar中实现的方法。

当seekbar的progress改变时onProgressRefresh()会被调用，它会调用setThumbPos()来设置thumb的位置。

大致过程就是这样，要更深入细致的了解还是得认真得看看代码。

现在我们知道，seekbar拥有的progressbar之外的功能，都是在absseekbar中实现的。系统默认seekbar是横着的，在absseekbar中计算progress、计算thumb的位置，用到了seekbar的宽和高，我们只要改变一下计算方法就能计算出竖着的seekbar所需要的各个数值。例如：

private void trackTouchEvent(MotionEvent event) {
final int Height = getHeight();
Log.d("demon", "Y:"+event.getY()+" height:"+Height);
final int available = Height - getPaddingBottom() - getPaddingTop();
int Y = (int)event.getY();
float scale;
float progress = 0;
if (Y > Height - getPaddingBottom()) {
scale = 0.0f;
} else if (Y < getPaddingTop()) {
scale = 1.0f;
} else {
scale = (float)(Height - getPaddingBottom()-Y) / (float)available;
}

final int max = getMax();
progress = scale * max;
setProgress((int) progress);
}

其他的地方你可以仿造这个写。

功能上分析告一段落，我们如何画出来一个竖着的seekbar呢？

我想了两个办法，一是自己画，也就是自己写个draw，太难，而且很难和系统风格统一。另外一个办法是让系统给我们画。verticalseekbar只是seekbar转了90度或-90度，我们可以把画布转一个角度，然后交给系统去画，具体的做法就是在ondraw()时调整画布，然后调用super.onDraw()。

这个调整也就是旋转和平移。至于旋转和平移的具体实现，我跟到native部分就没有看下去了，也没有看到具体的介绍。我的理解，你要保证画布的左上角在旋转平移以后坐标不变，否者会出现很多问题。 就我们的seekbar而言，如果你要获得一个向上增长的seekbar，那么代码应该是：

protected void onDraw(Canvas c)
{
c.rotate(-90);
c.translate(-height,0);//height是你的verticalseekbar的高
super.onDraw(c);
}

如果是向下的seekbar则应该是：

protected void onDraw(Canvas c)
{
c.rotate(90);
c.translate(0,-width);//width是你的verticalseekbar的宽
super.onDraw(c);
}

你也可以自己计算一下来验证。

一个View在屏幕上画出来，首先measure()会被调用，这是个final方法，measure()会调用onMeasure()。你可以重写onMeasure()，但是重写的onMeasure()中必须调用setMeasuredDimension(int,int)， setMeasuredDimension()会保存该View的长和宽。我们可以重写onMeasure()方法给我们的seekbar分配一块竖直的，长宽由我们设定的区域。在画seekbar之前，我们把这个区域旋转了90度交给系统，系统给我们画一个标准的seekbar，在整个layout中，这个seekbar就成竖直的了。

实际操作时，我们在工程中新建了类verticalSeekbar，把framework中seekbar的代码拷贝过来，做一些必须的修改(类名、构造方法什么的)。注意如果我们的verticalseekbar是在XML中定义的，在代码中使用findViewById()方法来获得，系统将使用第二个构造方法(我简单地试了一下，没有看到官方资料或权威的解释)，也就是

public SeekBar(Context context, AttributeSet attrs) {
this(context, attrs, com.android.internal.R.attr.seekBarStyle);
}

com.android.internal.R.attr.seekBarStyle在我我们的应用程序中是无法使用的，你可以换成android.R.attr.seekBarStyle，你也可以自己定义一个，但是必须包含系统本身的。

然后我们要加一些方法，也就是重写absseekbar中的一些方法，大致如下：


由于是给公司写的代码，不便共享，望大家见谅。贴俩实现了的图，鼓舞一下对verticalseekbar有需求的读者——做一个verticalseekbar不难。

欢迎收藏，不要盲目转载，你验证了我说的，在传播给别人。

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