一文读懂 Android TouchEvent 事件分发、拦截、处理过程

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什么是事件?事件是用户触摸手机屏幕,引起的一系列TouchEvent,包括ACTION_DOWN、ACTION_MOVE、ACTION_UP、ACTION_CANCEL等,这些action组合后变成点击事件、长按事件等。

在这文章中,用打Log测试的方法来了解Android TouchEvent 事件分发,拦截,处理过程。虽然看了一些其他的文章和源码及相关的资料,但是还是觉得需要打下Log和画图来了解一下,不然很容易忘记了事件传递的整个过程。所以写下这篇文章,达到看完这篇文章基本可以了解整个过程,并且可以自己画图画出来给别人看。

先看几个类,主要是画出一个3个ViewGroup叠加的界面,并在事件分发、拦截、处理时打下Log.

GitHub地址:https://github.com/libill/TouchEventDemo

一、通过打log分析事件分发

这里在一个Activity上添加三个ViewGroup来分析,这里值得注意的是Activity、View是没有onInterceptTouchEvent方法的。

一、了解Activity、ViewGroup1、ViewGroup2、ViewGroup3四个类

  1. activity_main.xml

     <?xml version="1.0" encoding="utf-8"?>
     	<android.support.constraint.ConstraintLayout xmlns:android="http://schemas.android.com/apk/res/android"
     xmlns:app="http://schemas.android.com/apk/res-auto"
     xmlns:tools="http://schemas.android.com/tools"
     android:layout_width="match_parent"
     android:layout_height="match_parent"
     tools:context="com.touchevent.demo.MyActivity">
     	<com.touchevent.demo.ViewGroup1
         android:layout_width="match_parent"
         android:layout_height="match_parent"
         android:background="@color/colorAccent">
         <com.touchevent.demo.ViewGroup2
             android:layout_width="match_parent"
             android:layout_height="match_parent"
             android:layout_margin="50dp"
             android:background="@color/colorPrimary">
             <com.touchevent.demo.ViewGroup3
                 android:layout_width="match_parent"
                 android:layout_height="match_parent"
                 android:layout_margin="50dp"
                 android:background="@color/colorPrimaryDark">
             </com.touchevent.demo.ViewGroup3>
         </com.touchevent.demo.ViewGroup2>
     	</com.touchevent.demo.ViewGroup1>
     </android.support.constraint.ConstraintLayout>  
    
  2. 主界面:MainActivity.java

     public class MyActivity extends AppCompatActivity {
         private final static String TAG = MyActivity.class.getName();
     
         @Override
         protected void onCreate(Bundle savedInstanceState) {
             super.onCreate(savedInstanceState);
             setContentView(R.layout.activity_main);
         }
     
         @Override
         public boolean dispatchTouchEvent(MotionEvent ev) {
             Log.i(TAG,"dispatchTouchEvent    action:" + StringUtils.getMotionEventName(ev));
             boolean superReturn = super.dispatchTouchEvent(ev);
             Log.d(TAG,"dispatchTouchEvent    action:" + StringUtils.getMotionEventName(ev) + " " + superReturn);
             return superReturn;
         }
     
         @Override
         public boolean onTouchEvent(MotionEvent ev) {
             Log.i(TAG,"onTouchEvent          action:" + StringUtils.getMotionEventName(ev));
             boolean superReturn = super.onTouchEvent(ev);
             Log.d(TAG,"onTouchEvent          action:" + StringUtils.getMotionEventName(ev) + " " + superReturn);
             return superReturn;
         }
     }
    
  3. 三个ViewGroup,里面的代码完全一样:ViewGroup1.java,ViewGroup2.java,ViewGroup3.java。由于代码一样所以只贴其中一个类。

     public class ViewGroup1 extends LinearLayout {
         private final static String TAG = ViewGroup1.class.getName();
     
         public ViewGroup1(Context context) {
             super(context);
         }
     
         public ViewGroup1(Context context,AttributeSet attrs) {
             super(context,attrs);
         }
     
         @Override
         public boolean dispatchTouchEvent(MotionEvent ev) {
             Log.i(TAG,"dispatchTouchEvent    action:" + StringUtils.getMotionEventName(ev) + " " + superReturn);
             return superReturn;
         }
     
         @Override
         public boolean onInterceptTouchEvent(MotionEvent ev) {
             Log.i(TAG,"onInterceptTouchEvent action:" + StringUtils.getMotionEventName(ev));
             boolean superReturn = super.onInterceptTouchEvent(ev);
             Log.d(TAG,"onInterceptTouchEvent action:" + StringUtils.getMotionEventName(ev) + " " + superReturn);
             return superReturn;
         }
     
         @Override
         public boolean onTouchEvent(MotionEvent ev) {
             Log.i(TAG,"onTouchEvent          action:" + StringUtils.getMotionEventName(ev) + " " + superReturn);
             return superReturn;
         }
     }
    

二、不拦截处理任何事件

添加没有拦截处理任何事件的代码,看看事件是怎么传递的,选择Info,查看Log.

从流程图可以看出,事件分发从Activity开始,然后分发到ViewGroup,在这个过程中,只要ViewGroup没有拦截处理,最后还是会回到Activity的onTouchEvent方法

三、ViewGroup2的dispatchTouchEvent返回true

把ViewGroup2.java的dispatchTouchEvent修改一下,return 返回true使事件不在分发

@Override
public boolean dispatchTouchEvent(MotionEvent ev) {
 Log.i(TAG,"dispatchTouchEvent    action:" + StringUtils.getMotionEventName(ev));
 Log.d(TAG,"onInterceptTouchEvent action:" + StringUtils.getMotionEventName(ev) + " " + true);
 return true;
}

此时的Log

图片可以看出,当ViewGroupon2的dispatchTouchEvent返回true后,事件不会再分发传送到ViewGroup3了,也不会分发到Activity的onTouchEvent了。而是事件到了ViewGroupon2的dispatchTouchEvent后,就停止了。dispatchTouchEvent返回true表示着事件不用再分发下去了。

四、ViewGroup2的onInterceptTouchEvent返回true

把ViewGroup2.java的onInterceptTouchEvent修改一下,return 返回true把事件拦截

@Override
public boolean dispatchTouchEvent(MotionEvent ev) {
    Log.i(TAG,"dispatchTouchEvent    action:" + StringUtils.getMotionEventName(ev));
    boolean superReturn = super.dispatchTouchEvent(ev);
    Log.d(TAG,"dispatchTouchEvent    action:" + StringUtils.getMotionEventName(ev) + " " + superReturn);
    return superReturn;
}

@Override
public boolean onInterceptTouchEvent(MotionEvent ev) {
    Log.i(TAG,"onInterceptTouchEvent action:" + StringUtils.getMotionEventName(ev));
    Log.d(TAG,"onInterceptTouchEvent action:" + StringUtils.getMotionEventName(ev) + " " + true);
    return true;
}

此时的Log


@H_404_99@

可以看出ViewGroup2拦截了事件,就不会继续分发到ViewGroup3;而且ViewGroup3拦截了事件又不处理事件,会把事件传递到Activity的onTouchEvent方法

五、ViewGroup2的onInterceptTouchEvent、onTouchEvent返回true

把ViewGroup2.java的onTouchEvent修改一下,return 返回true把事件处理了

@Override
public boolean onInterceptTouchEvent(MotionEvent ev) {
    Log.i(TAG,"onInterceptTouchEvent action:" + StringUtils.getMotionEventName(ev) + " " + true);
    return true;
}

@Override
public boolean onTouchEvent(MotionEvent ev) {
    Log.i(TAG,"onTouchEvent          action:" + StringUtils.getMotionEventName(ev));
    Log.d(TAG,"onTouchEvent          action:" + StringUtils.getMotionEventName(ev) + " " + true);
    return true;
}


从流程可以总结出,当ViewGroup2的onInterceptTouchEvent、onTouchEvent都返回true时,事件最终会走到ViewGroup2的onTouchEvent方法处理事件,后续的事件都会走到这里来。

上面通过log分析很清楚了,是不是就这样够了?其实还不行,还要从源码的角度去分析下,为什么事件会这样分发。

二、通过源码分析事件分发

一、Activity的dispatchTouchEvent

先看看Activity下的dispatchTouchEvent

public boolean dispatchTouchEvent(MotionEvent ev) {
    if (ev.getAction() == MotionEvent.ACTION_DOWN) {
        onUserInteraction();
    }
    if (getWindow().superDispatchTouchEvent(ev)) {
        return true;
    }
    return onTouchEvent(ev);
}

onUserInteraction方法

public void onUserInteraction() {
}

代码可以了解

  1. 调用Activity的onUserInteraction方法,action为down时会进去onUserInteraction方法,但是这个是空方法不做任何事情,可以忽略。

  2. 调用window的superDispatchTouchEvent方法,返回true时事件分发处理结束,否则会调用Activity的onTouchEvent方法

  3. 调用Activity的onTouchEvent方法,进入这个条件的方法是window的superDispatchTouchEvent方法返回false。从上面的分析(二、不拦截处理任何事件)可以知道,所有子View的dispatchTouchEvent、onInterceptTouchEvent、onTouchEvent都返回false时会调动Activity的onTouchEvent方法,这个时候也是使window的superDispatchTouchEvent方法返回false成立。

二、window的superDispatchTouchEvent

Activity的getWindow方法

public Window getWindow() {
    return mWindow;
}

mWindow是如何赋值的?
是在Activity的attach方法赋值的,其实mWindow是PhoneWindow。

Activity的attach方法

final void attach(Context context,ActivityThread aThread,Instrumentation instr,IBinder token,int ident,Application application,Intent intent,ActivityInfo info,CharSequence title,Activity parent,String id,NonConfigurationInstances lastNonConfigurationInstances,Configuration config,String referrer,IVoiceInteractor voiceInteractor,Window window,ActivityConfigCallback activityConfigCallback) {
    attachBaseContext(context);

    mFragments.attachHost(null /*parent*/);

    mWindow = new PhoneWindow(this,window,activityConfigCallback);
    mWindow.setWindowControllerCallback(this);
    mWindow.setCallback(this);
    mWindow.setOnWindowDismissedCallback(this);
    mWindow.getLayoutInflater().setPrivateFactory(this);
	...
}

PhoneWindow的superDispatchTouchEvent方法

private DecorView mDecor;

@Override
public boolean superDispatchTouchEvent(MotionEvent event) {
    return mDecor.superDispatchTouchEvent(event);
}

DevorView的superDispatchTouchEvent

public boolean superDispatchTouchEvent(MotionEvent event) {
    return super.dispatchTouchEvent(event);
}

而mDecor是一个继承FrameLayout的DecorView,就这样把事件分发到ViewGroup上了。

三、ViewGroup的dispatchTouchEvent

3.1 ViewGroup拦截事件的情况

        // Check for interception.
        final boolean intercepted;
        if (actionMasked == MotionEvent.ACTION_DOWN
                || mFirstTouchTarget != null) {
            final boolean disallowIntercept = (mGroupFlags & FLAG_DISALLOW_INTERCEPT) != 0;
            if (!disallowIntercept) {
                intercepted = onInterceptTouchEvent(ev);
                ev.setAction(action); // restore action in case it was changed
            } else {
                intercepted = false;
            }
        } else {
            // There are no touch targets and this action is not an initial down
            // so this view group continues to intercept touches.
            intercepted = true;
        }

这里分为2种情况会判断是否需要拦截,也就是当某一条件成立时,会执行onInterceptTouchEvent判断是否需要拦截事件。

  1. 当actionMasked == MotionEvent.ACTION_DOWN时。

  2. 当mFirstTouchTarget != null时。mFirstTouchTarget是成功处理事件的ViewGroup的子View,也就是ViewGroup的子View在以下情况返回true时,这个在log分析流程图轻易得到:

    2.1 dispatchTouchEvent返回true

    2.2 如果子View是ViewGroup时,onInterceptTouchEvent、onTouchEvent返回true

另外还有一种情况是disallowIntercept为true时,intercepted直接赋值false不进行拦截。FLAG_DISALLOW_INTERCEPT是通过requestDisallowInterceptTouchEvent方法来设置的,用于在子View中设置,设置后ViewGroup只能拦截down事件,无法拦截其他move、up、cancel事件。为什么ViewGroup还能拦截down事件呢?因为ViewGroup在down事件时进行了重置,看看以下代码

// Handle an initial down.
if (actionMasked == MotionEvent.ACTION_DOWN) {
    // Throw away all prevIoUs state when starting a new touch gesture.
    // The framework may have dropped the up or cancel event for the prevIoUs gesture
    // due to an app switch,ANR,or some other state change.
    cancelAndClearTouchTargets(ev);
    resetTouchState();
}

private void resetTouchState() {
    clearTouchTargets();
    resetCancelNextUpFlag(this);
    mGroupFlags &= ~FLAG_DISALLOW_INTERCEPT;
    mNestedScrollAxes = SCROLL_AXIS_NONE;
}

通过源码可以了解到,ViewGroup拦截事件后,不再调用onInterceptTouchEvent,而是直接交给mFirstTouchTarget的onTouchEvent处理,如果该onTouchEvent不处理最终会交给Activity的onTouchEvent。

3.2 ViewGroup不拦截事件的情况

ViewGroup不拦截事件时,会遍历子View,使事件分发到子View进行处理。

final View[] children = mChildren;
for (int i = childrenCount - 1; i >= 0; i--) {
    final int childIndex = getAndVerifyPreorderedIndex(
            childrenCount,i,customOrder);
    final View child = getAndVerifyPreorderedView(
            preorderedList,children,childIndex);

    // If there is a view that has accessibility focus we want it
    // to get the event first and if not handled we will perform a
    // normal dispatch. We may do a double iteration but this is
    // safer given the timeframe.
    if (childWithAccessibilityFocus != null) {
        if (childWithAccessibilityFocus != child) {
            continue;
        }
        childWithAccessibilityFocus = null;
        i = childrenCount - 1;
    }

    if (!canViewReceivePointerEvents(child)
            || !isTransformedTouchPointInView(x,y,child,null)) {
        ev.setTargetAccessibilityFocus(false);
        continue;
    }

    newTouchTarget = getTouchTarget(child);
    if (newTouchTarget != null) {
        // Child is already receiving touch within its bounds.
        // Give it the new pointer in addition to the ones it is handling.
        newTouchTarget.pointerIdBits |= idBitsToAssign;
        break;
    }

    resetCancelNextUpFlag(child);
    if (dispatchTransformedTouchEvent(ev,false,idBitsToAssign)) {
        // Child wants to receive touch within its bounds.
        mLastTouchDownTime = ev.getDownTime();
        if (preorderedList != null) {
            // childIndex points into presorted list,find original index
            for (int j = 0; j < childrenCount; j++) {
                if (children[childIndex] == mChildren[j]) {
                    mLastTouchDownIndex = j;
                    break;
                }
            }
        } else {
            mLastTouchDownIndex = childIndex;
        }
        mLastTouchDownX = ev.getX();
        mLastTouchDownY = ev.getY();
        newTouchTarget = addTouchTarget(child,idBitsToAssign);
        alreadyDispatchedToNewTouchTarget = true;
        break;
    }
}
3.2.1 寻找可接收事件的子View

通过canViewReceivePointerEvents判断子View是否能够接收到点击事件。必须符合2种情况,缺一不可:1、点击事件的坐标落在在子View的区域内;2、子View没有正在播放动画。满足条件后,调用dispatchTransformedTouchEvent,其实也是调用子View的dispatchTouchEvent。

private static boolean canViewReceivePointerEvents(@NonNull View child) {
    return (child.mViewFlags & VISIBILITY_MASK) == VISIBLE
            || child.getAnimation() != null;
}

protected boolean isTransformedTouchPointInView(float x,float y,View child,PointF outLocalPoint) {
    final float[] point = getTempPoint();
    point[0] = x;
    point[1] = y;
    transformPointToViewLocal(point,child);
    final boolean isInView = child.pointInView(point[0],point[1]);
    if (isInView && outLocalPoint != null) {
        outLocalPoint.set(point[0],point[1]);
    }
    return isInView;
}

private boolean dispatchTransformedTouchEvent(MotionEvent event,boolean cancel,int desiredPointerIdBits) {
    final boolean handled;
    final int oldAction = event.getAction();
    if (cancel || oldAction == MotionEvent.ACTION_CANCEL) {
        event.setAction(MotionEvent.ACTION_CANCEL);
        if (child == null) {
            handled = super.dispatchTouchEvent(event);
        } else {
            handled = child.dispatchTouchEvent(event);
        }
        event.setAction(oldAction);
        return handled;
    }

    ...

    // Perform any necessary transformations and dispatch.
    if (child == null) {
        handled = super.dispatchTouchEvent(transformedEvent);
    } else {
        final float offsetX = mScrollX - child.mLeft;
        final float offsetY = mScrollY - child.mTop;
        transformedEvent.offsetLocation(offsetX,offsetY);
        if (! child.hasIdentityMatrix()) {
            transformedEvent.transform(child.getInverseMatrix());
        }

        handled = child.dispatchTouchEvent(transformedEvent);
    }

    // Done.
    transformedEvent.recycle();
    return handled;
}

当dispatchTransformedTouchEvent返回true时,结束for循环遍历,赋值newTouchTarget,相当于发现了可以接收事件的View,不用再继续找了。

newTouchTarget = addTouchTarget(child,idBitsToAssign);
alreadyDispatchedToNewTouchTarget = true;
break;

在addTouchTarget方法赋值mFirstTouchTarget。

private TouchTarget addTouchTarget(@NonNull View child,int pointerIdBits) {
    final TouchTarget target = TouchTarget.obtain(child,pointerIdBits);
    target.next = mFirstTouchTarget;
    mFirstTouchTarget = target;
    return target;
}
3.2.2 ViewGroup自己处理事件

另一种情况是mFirstTouchTarget为空时,ViewGroup自己处理事件,这里注意第三个参数为null,ViewGroup的super.dispatchTouchEvent将调用View的dispatchTouchEvent。

if (mFirstTouchTarget == null) {
    // No touch targets so treat this as an ordinary view.
    handled = dispatchTransformedTouchEvent(ev,canceled,null,TouchTarget.ALL_POINTER_IDS);
}

3.3 View处理点击事件的过程

View的dispatchTouchEvent是怎么处理事件的呢?

public boolean dispatchTouchEvent(MotionEvent event) {
    boolean result = false;
	...
    if (onFilterTouchEventForSecurity(event)) {
        if ((mViewFlags & ENABLED_MASK) == ENABLED && handleScrollBarDragging(event)) {
            result = true;
        }
        //noinspection SimplifiableIfStatement
        ListenerInfo li = mListenerInfo;
        if (li != null && li.mOnTouchListener != null
                && (mViewFlags & ENABLED_MASK) == ENABLED
                && li.mOnTouchListener.onTouch(this,event)) {
            result = true;
        }

        if (!result && onTouchEvent(event)) {
            result = true;
        }
    }
	...
    return result;
}
  1. 首先使用onFilterTouchEventForSecurity方法过滤不符合应用安全策略的触摸事件。

     public boolean onFilterTouchEventForSecurity(MotionEvent event) {
         //noinspection RedundantIfStatement
         if ((mViewFlags & FILTER_TOUCHES_WHEN_OBSCURED) != 0
                 && (event.getFlags() & MotionEvent.FLAG_WINDOW_IS_OBSCURED) != 0) {
             // Window is obscured,drop this touch.
             return false;
         }
         return true;
     }
    
  2. mOnTouchListener != null判断是否设置了OnTouchEvent,设置了就执行mOnTouchListener.onTouch并返回true,不再执行onTouchEvent。这里得出OnTouchEvent的优先级高于OnTouchEvent,便于使用setOnTouchListener设置处理点击事件。

  3. 另一种情况是进入onTouchEvent进行处理。

     public boolean onTouchEvent(MotionEvent event) {
         final float x = event.getX();
         final float y = event.getY();
         final int viewFlags = mViewFlags;
         final int action = event.getAction();
     
         final boolean clickable = ((viewFlags & CLICKABLE) == CLICKABLE
                 || (viewFlags & LONG_CLICKABLE) == LONG_CLICKABLE)
                 || (viewFlags & CONTEXT_CLICKABLE) == CONTEXT_CLICKABLE;
     
         if ((viewFlags & ENABLED_MASK) == DISABLED) {
             if (action == MotionEvent.ACTION_UP && (mPrivateFlags & PFLAG_PRESSED) != 0) {
                 setPressed(false);
             }
             mPrivateFlags3 &= ~PFLAG3_FINGER_DOWN;
             // A disabled view that is clickable still consumes the touch
             // events,it just doesn't respond to them.
             return clickable;
         }
     	...
     }
    

当View不可用时,依然会处理事件,只是看起来不可用。

接着执行mTouchDelegate.onTouchEvent

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

下面看看up事件是怎么处理的

/**
 * <p>Indicates this view can display a tooltip on hover or long press.</p>
 * {@hide}
 */
static final int TOOLTIP = 0x40000000;

if (clickable || (viewFlags & TOOLTIP) == TOOLTIP) {
    switch (action) {
        case MotionEvent.ACTION_UP:
            mPrivateFlags3 &= ~PFLAG3_FINGER_DOWN;
            if ((viewFlags & TOOLTIP) == TOOLTIP) {
                handleTooltipUp();
            }
            if (!clickable) {
                removeTapCallback();
                removeLongPressCallback();
                mInContextButtonPress = false;
                mHasPerformedLongPress = false;
                mIgnoreNextUpEvent = false;
                break;
            }
            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,x,y);
                }

                if (!mHasPerformedLongPress && !mIgnoreNextUpEvent) {
                    // 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)) {
                            performClickInternal();
                        }
                    }
                }

                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();
            }
            mIgnoreNextUpEvent = false;
            break;
            ...
    }

    return true;
}

从上面代码可以了解,clickable、TOOLTIP(长按)有一个为true时,就会消耗事件,使onTouchEvent返回true。其中PerformClick内部调用了performClick方法

public boolean performClick() {
    // We still need to call this method to handle the cases where performClick() was called
    // externally,instead of through performClickInternal()
    notifyAutofillManagerOnClick();

    final boolean result;
    final ListenerInfo li = mListenerInfo;
    if (li != null && li.mOnClickListener != null) {
        playSoundEffect(SoundEffectConstants.CLICK);
        li.mOnClickListener.onClick(this);
        result = true;
    } else {
        result = false;
    }

    sendAccessibilityEvent(AccessibilityEvent.TYPE_VIEW_CLICKED);

    notifyEnterOrExitForAutoFillIfNeeded(true);

    return result;
}

如果View设置了OnClickListener,那performClick会调用内部的onClick方法

public void setOnClickListener(@Nullable OnClickListener l) {
    if (!isClickable()) {
        setClickable(true);
    }
    getListenerInfo().mOnClickListener = l;
}

public void setOnLongClickListener(@Nullable OnLongClickListener l) {
    if (!isLongClickable()) {
        setLongClickable(true);
    }
    getListenerInfo().mOnLongClickListener = l;
}

通过setOnClickListener设置clickable,通过setOnLongClickListener设置LONG_CLICKABLE长按事件。设置后使得onTouchEvent返回true。到这里我们已经分析完成点击事件的分发过程了。

本文地址:http://libill.github.io/2019/09/09/android-touch-event/

本文参考以下内容

1、《Android开发艺术探索》

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这节主要是讲解jsoup解析HTML页面。由于在android开发过程中,不可避免的涉及到web页面的抓取,解析,展示等等,所以,在这里我主要展示下利用jsoup jar包来抓取cnbeta.com网
Android开发探秘之一:创建可以点击的Button
在Android开发过程中,很多人都熟悉Intent,这是个用于在多个View之间共享数据的类。本节主要是继承上节,通过点选ListView中的文本,把文本中的URL加载到一个新的页面上,并且打印出来
运行环境 Android Studio 4.1.1 compileSdkVersion 29 buildToolsVersion &quot;29.0.2&quot; 点击绿色锤子「make proj
&quot;原文链接&quot; 使用 ConstraintLayout 构建自适应界面 ConstraintLayout 可让您使用扁平视图层次结构(无嵌套视图组)创建复杂的大型布局。它与 Rela
WorkManager工作约束,延迟与查询工作 本文可能会混用“工作”与“任务”这两个词。 本文例子使用Kotlin 准备一个工作类(任务)UploadWorker2 class UploadWork
Android教程,View.post方法流程分析。View.post与Handler的post方法有何不同?先来简单看一下Handler的post(Runnable)方法。这个方法是将一个Runna
简介 某些音乐播放或者视频播放的界面上,资源还在加载时,进度条的原点(thumb)会显示一个转圈的效果。 资源加载完成后,又切换回静态效果。这个效果增强了用户体验。 一般来说有美术人员负责设计和切图。
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