android 点击button状态变化实现分析

前言

在写应用时 ,布局中设置了一个button之后点击这个button,button的背景就会变化,我们什么都没干就有了这个效果,最近项目正好涉及到相关的绘制,就去源码里面看一下点击时的实现。关于点击事件的传递我在的android 中事件传递分析 已经学习过了,其中还涉及到view的绘制view绘制流程

内容

点击某个button时,首先时ViewGroup接收到这个事件然后分发下去dispatchTouchEvent,最后到了你的button的(button继承自view)的onTouchEvent中


    /**
     * Implement this method to handle touch screen motion events.
     * <p>
     * If this method is used to detect click actions, it is recommended that
     * the actions be performed by implementing and calling
     * {@link #performClick()}. This will ensure consistent system behavior,
     * including:
     * <ul>
     * <li>obeying click sound preferences
     * <li>dispatching OnClickListener calls
     * <li>handling {@link AccessibilityNodeInfo#ACTION_CLICK ACTION_CLICK} when
     * accessibility features are enabled
     * </ul>
     *
     * @param event The motion event.
     * @return True if the event was handled, false otherwise.
     */
    public boolean onTouchEvent(MotionEvent event) {
        final int viewFlags = mViewFlags;

        if ((viewFlags & ENABLED_MASK) == DISABLED) {
                      if (event.getAction() == MotionEvent.ACTION_UP && (mPrivateFlags & PFLAG_PRESSED) != 0) {
                setPressed(false);
//            final int action = event.getAction();
//            if (action == MotionEvent.ACTION_UP || action == MotionEvent.ACTION_CANCEL) {
//                if ((mPrivateFlags & PFLAG_PRESSED) != 0) {
//                    setPressed(false);
//                } else if ((mPrivateFlags & PFLAG_PREPRESSED) != 0) {
//                    removeTapCallback();
//                }
            }
            // A disabled view that is clickable still consumes the touch
            // events, it just doesn't respond to them.
            return (((viewFlags & CLICKABLE) == CLICKABLE ||
                    (viewFlags & LONG_CLICKABLE) == LONG_CLICKABLE));
        }

        if (mTouchDelegate != null) {
            if (mTouchDelegate.onTouchEvent(event)) {
                return true;
            }
        }

        if (((viewFlags & CLICKABLE) == CLICKABLE ||
                (viewFlags & LONG_CLICKABLE) == LONG_CLICKABLE)) {
            switch (event.getAction()) {
                case MotionEvent.ACTION_UP:
                    boolean prepressed = (mPrivateFlags & PFLAG_PREPRESSED) != 0;
                    if ((mPrivateFlags & PFLAG_PRESSED) != 0 || prepressed) {
                        // take focus if we don't have it already and we should in
                        // touch mode.
                        boolean focusTaken = false;
                        if (isFocusable() && isFocusableInTouchMode() && !isFocused()) {
                            focusTaken = requestFocus();
                        }

                        if (prepressed) {
                            // The button is being released before we actually
                            // showed it as pressed.  Make it show the pressed
                            // state now (before scheduling the click) to ensure
                            // the user sees it.
                            setPressed(true);
                       }

                        if (!mHasPerformedLongPress) {
                            // This is a tap, so remove the longpress check
                            removeLongPressCallback();

                            // Only perform take click actions if we were in the pressed state
                            if (!focusTaken) {
                                // Use a Runnable and post this rather than calling
                                // performClick directly. This lets other visual state
                                // of the view update before click actions start.
                                if (mPerformClick == null) {
                                    mPerformClick = new PerformClick();
                                }
                                if (!post(mPerformClick)) {
                                    performClick();
                                }
                            }
                        }

                        if (mUnsetPressedState == null) {
                            mUnsetPressedState = new UnsetPressedState();
                        }

                        if (prepressed) {
                            postDelayed(mUnsetPressedState,
                                    ViewConfiguration.getPressedStateDuration());
                        } else if (!post(mUnsetPressedState)) {
                            // If the post failed, unpress right now
                            mUnsetPressedState.run();
                        }
                        removeTapCallback();
                    }
                    break;

                case MotionEvent.ACTION_DOWN: //这个地方时你按下view的响应
                    mHasPerformedLongPress = false;

                    if (performButtonActionOnTouchDown(event)) {
                        break;
                    }

                    // Walk up the hierarchy to determine if we're inside a scrolling container.
                    boolean isInScrollingContainer = isInScrollingContainer();

                    // For views inside a scrolling container, delay the pressed feedback for
                    // a short period in case this is a scroll.
                    if (isInScrollingContainer) {
                        mPrivateFlags |= PFLAG_PREPRESSED;
                        if (mPendingCheckForTap == null) {
                            mPendingCheckForTap = new CheckForTap();
                        }
                        postDelayed(mPendingCheckForTap, ViewConfiguration.getTapTimeout());
                    } else {
                        // Not inside a scrolling container, so show the feedback right away
                        setPressed(true);// 这里设置按下为true
                        checkForLongClick(0);
                    }
                    break;

                case MotionEvent.ACTION_CANCEL:
                    setPressed(false);
                    removeTapCallback();
                    removeLongPressCallback();
                    break;

                case MotionEvent.ACTION_MOVE:
                    final int x = (int) event.getX();
                    final int y = (int) event.getY();

                    // Be lenient about moving outside of buttons
                    if (!pointInView(x, y, mTouchSlop)) {
                        // Outside button
                        removeTapCallback();
                        if ((mPrivateFlags & PFLAG_PRESSED) != 0) {
                            // Remove any future long press/tap checks
                            removeLongPressCallback();

                            setPressed(false);
                        }
                    }
                    break;
            }
            return true;
        }

        return false;
    }

setPressed(true); 那就走到了setPressed里面

/**
     * Sets the pressed state for this view.
     *
     * @see #isClickable()
     * @see #setClickable(boolean)
     *
     * @param pressed Pass true to set the View's internal state to "pressed", or false to reverts
     *        the View's internal state from a previously set "pressed" state.
     */
    public void setPressed(boolean pressed) {
        final boolean needsRefresh = pressed != ((mPrivateFlags & PFLAG_PRESSED) == PFLAG_PRESSED);

        if (pressed) {
            mPrivateFlags |= PFLAG_PRESSED;
        } else {
            mPrivateFlags &= ~PFLAG_PRESSED;
        }

        if (needsRefresh) { //是否需要刷新,当然要啦!
            refreshDrawableState();
        }
        dispatchSetPressed(pressed);
    }

看看refreshDrawableState 这里是干了什么

 /**
     * Call this to force a view to update its drawable state. This will cause
     * drawableStateChanged to be called on this view. Views that are interested
     * in the new state should call getDrawableState.
     *
     * @see #drawableStateChanged
     * @see #getDrawableState
     */
    public void refreshDrawableState() {
        mPrivateFlags |= PFLAG_DRAWABLE_STATE_DIRTY;
        drawableStateChanged();

        ViewParent parent = mParent;
        if (parent != null) {
            parent.childDrawableStateChanged(this);//如果是个父视图的话,子view也相应更新。
        }
    }

看代码的时候注意看方法上面的注释,对我们理解流程有很大的帮组,上面说一会调drawableStateChanged这个方法,我们一会看看时在那里回调的。下面看看 drawableStateChanged(),

 private Drawable mBackground;
 /**
     * This function is called whenever the state of the view changes in such
     * a way that it impacts the state of drawables being shown.
     *
     * <p>Be sure to call through to the superclass when overriding this
     * function.
     *
     * @see Drawable#setState(int[])
     */
    protected void drawableStateChanged() {
        Drawable d = mBackground;
        if (d != null && d.isStateful()) {
            d.setState(getDrawableState());
        }
    }

看到了 这个地方给drawable设置了一个新的状态,通过getDrawableState()的值设置下去

 /**
     * Return an array of resource IDs of the drawable states representing the
     * current state of the view.
     *
     * @return The current drawable state
     *
     * @see Drawable#setState(int[])
     * @see #drawableStateChanged()
     * @see #onCreateDrawableState(int)
     */
    public final int[] getDrawableState() {
        if ((mDrawableState != null) && ((mPrivateFlags & PFLAG_DRAWABLE_STATE_DIRTY) == 0)) {
            return mDrawableState;
        } else {
            mDrawableState = onCreateDrawableState(0);
            mPrivateFlags &= ~PFLAG_DRAWABLE_STATE_DIRTY;
            return mDrawableState;
        }
    }

然后看看上面d.setState()这个方法里面, drawable 是一个抽象类,看看它的setState方法,


    /**
     * Specify a set of states for the drawable. These are use-case specific,
     * so see the relevant documentation. As an example, the background for
     * widgets like Button understand the following states:
     * [{@link android.R.attr#state_focused},
     *  {@link android.R.attr#state_pressed}].
     *
     * <p>If the new state you are supplying causes the appearance of the
     * Drawable to change, then it is responsible for calling
     * {@link #invalidateSelf} in order to have itself redrawn, <em>and</em>
     * true will be returned from this function.
     *
     * <p>Note: The Drawable holds a reference on to <var>stateSet</var>
     * until a new state array is given to it, so you must not modify this
     * array during that time.</p>
     *
     * @param stateSet The new set of states to be displayed.
     *
     * @return Returns true if this change in state has caused the appearance
     * of the Drawable to change (hence requiring an invalidate), otherwise
     * returns false.
     */
    public boolean setState(final int[] stateSet) {
        if (!Arrays.equals(mStateSet, stateSet)) {
            mStateSet = stateSet;
            return onStateChange(stateSet);
        }
        return false;
    }

   /**
     * Override this in your subclass to change appearance if you recognize the
     * specified state.
     *
     * @return Returns true if the state change has caused the appearance of
     * the Drawable to change (that is, it needs to be drawn), else false
     * if it looks the same and there is no need to redraw it since its
     * last state.
     */
    protected boolean onStateChange(int[] state) { return false; }

Override this in your subclass ,这个方法会在drawable的子类中实现,那就要找找是哪一个子类实现了这个方法了。找了半天都没有找到哪里有指定drawable的子类,但是功夫不负苦心人,看到了setBackgroundDrawable 这个方法在view当中,

 /**
     * @deprecated use {@link #setBackground(Drawable)} instead
     */
    @Deprecated
    public void setBackgroundDrawable(Drawable background) {
        computeOpaqueFlags();

        if (background == mBackground) {
            return;
        }
    ....
  mBackground = background; // 你设什么类型下来,我就是怎么类型。button多个状态那肯定就是StateListDrawable了,StateListDrawable又继承自DrawableContainer,DrawableContainer继承自Drawable.
} onStateChange

那就看看StateListDrawable里面的onStateChange方法

 @Override
    protected boolean onStateChange(int[] stateSet) {
        int idx = mStateListState.indexOfStateSet(stateSet);
        if (DEBUG) android.util.Log.i(TAG, "onStateChange " + this + " states "
                + Arrays.toString(stateSet) + " found " + idx);
        if (idx < 0) {
            idx = mStateListState.indexOfStateSet(StateSet.WILD_CARD);
        }
        if (selectDrawable(idx)) {
            return true;
        }
        return super.onStateChange(stateSet);
    }

看到了selectDrawable,亲人啊,selectDrawable是在它的父类DrawableContainer里面实现的,

 public boolean selectDrawable(int idx) {
        if (idx == mCurIndex) {
            return false;
        }

        final long now = SystemClock.uptimeMillis();

        if (DEBUG) android.util.Log.i(TAG, toString() + " from " + mCurIndex + " to " + idx
                + ": exit=" + mDrawableContainerState.mExitFadeDuration
                + " enter=" + mDrawableContainerState.mEnterFadeDuration);

        if (mDrawableContainerState.mExitFadeDuration > 0) {
            if (mLastDrawable != null) {
                mLastDrawable.setVisible(false, false);
            }
            if (mCurrDrawable != null) {
                mLastDrawable = mCurrDrawable;
                mExitAnimationEnd = now + mDrawableContainerState.mExitFadeDuration;
            } else {
                mLastDrawable = null;
                mExitAnimationEnd = 0;
            }
        } else if (mCurrDrawable != null) {
            mCurrDrawable.setVisible(false, false);
        }

        if (idx >= 0 && idx < mDrawableContainerState.mNumChildren) {
            final Drawable d = mDrawableContainerState.getChild(idx);
            mCurrDrawable = d;
            mCurIndex = idx;
            if (d != null) {
                mInsets = d.getOpticalInsets();
                d.mutate();
                if (mDrawableContainerState.mEnterFadeDuration > 0) {
                    mEnterAnimationEnd = now + mDrawableContainerState.mEnterFadeDuration;
                } else {
                    d.setAlpha(mAlpha);
                }
                d.setVisible(isVisible(), true);
                d.setDither(mDrawableContainerState.mDither);
                d.setColorFilter(mColorFilter);
                d.setState(getState());
                d.setLevel(getLevel());
                d.setBounds(getBounds());
                d.setLayoutDirection(getLayoutDirection());
                d.setAutoMirrored(mDrawableContainerState.mAutoMirrored);
            } else {
                mInsets = Insets.NONE;
            }
        } else {
            mCurrDrawable = null;
            mInsets = Insets.NONE;
            mCurIndex = -1;
        }

        if (mEnterAnimationEnd != 0 || mExitAnimationEnd != 0) {
            if (mAnimationRunnable == null) {
                mAnimationRunnable = new Runnable() {
                    @Override public void run() {
                        animate(true);
                        invalidateSelf();
                    }
                };
            } else {
                unscheduleSelf(mAnimationRunnable);
            }
            // Compute first frame and schedule next animation.
            animate(true);
        }

        invalidateSelf();// 终于看到了invalidateSelf 方法了之前setState的注释里面有提到这个方法

        return true;
    }

invalidateSelf方法的实现在drawable里面,这里你需要知道view是有实现Drawable的callback接口的,**public class View implements Drawable.Callback, KeyEvent.Callback,AccessibilityEventSource **

  /**
     * Use the current {@link Callback} implementation to have this Drawable
     * redrawn.  Does nothing if there is no Callback attached to the
     * Drawable.
     *
     * @see Callback#invalidateDrawable
     * @see #getCallback() 
     * @see #setCallback(android.graphics.drawable.Drawable.Callback) 
     */
    public void invalidateSelf() {
        final Callback callback = getCallback();
        if (callback != null) {
            callback.invalidateDrawable(this);//这个时候就回到了view 里面的invalidateDrawable方法里了
        }
    }

View.java中

  /**
     * Invalidates the specified Drawable.
     *
     * @param drawable the drawable to invalidate
     */
    public void invalidateDrawable(Drawable drawable) {
        if (verifyDrawable(drawable)) {
            final Rect dirty = drawable.getBounds();
            final int scrollX = mScrollX;
            final int scrollY = mScrollY;

            invalidate(dirty.left + scrollX, dirty.top + scrollY,
                    dirty.right + scrollX, dirty.bottom + scrollY); // view 的刷新
        }
    }

invalidate 的刷新是通知了逐层上传,然后最终从父类开始重绘。ok!

invalidate 流程

关于invalidate的刷新可以看invalidate 分析 的5-3

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