Android原理——自定义Toast原理

自定义Toast原理

概要
1. 使用Toast遇到的问题
2. Toast源码及原理
3. 我的单例类 T.java

使用Toast遇到的问题

• 原生的Toast真的很难看不是吗

• 多个Toast依次显示，程序都结束了还在不停的显示呢

  解决办法：自定义Toast ＋ 单例类

---

Toast源码及原理

Toast的源码不多，只有423行

有些我们常用的方法，想必不用多说，例如：
public Toast(Context context)
public void show()
public void cancel()
public static Toast makeText(Context context, int resId, int duration)
public static Toast makeText(Context context, CharSequence text, int duration)

重要的是：
有一个内部类TN(其实是一个Binder)，是TransientNotification的缩写 短暂的通知

private static class TN extends ITransientNotification.Stub {

        final Runnable mShow = new Runnable() {
            public void run() {
                handleShow();
            }
        };

        final Runnable mHide = new Runnable() {
            public void run() {
                handleHide();
                // Don't do this in handleHide() because it is also invoked by handleShow()
                mNextView = null;
            }
        };

        private final WindowManager.LayoutParams mParams = new WindowManager.LayoutParams();
        final Handler mHandler = new Handler();    

        int mGravity = Gravity.CENTER_HORIZONTAL | Gravity.BOTTOM;
        int mX, mY;
        float mHorizontalMargin;
        float mVerticalMargin;

        /**
         * @me: mNextView是Toast要显示的View
         */
        View mView;
        View mNextView;

        WindowManagerImpl mWM;

        /**
         * @me: 这里有些值得注意的 params.flags
         * 使其不可点击，不可获取焦点，保证屏幕高亮
         * 窗口类型为WindowManager.LayoutParams.TYPE_TOAST
         */
        TN() {
            // XXX This should be changed to use a Dialog, with a Theme.Toast
            // defined that sets up the layout params appropriately.
            final WindowManager.LayoutParams params = mParams;
            params.height = WindowManager.LayoutParams.WRAP_CONTENT;
            params.width = WindowManager.LayoutParams.WRAP_CONTENT;
            params.flags = WindowManager.LayoutParams.FLAG_NOT_FOCUSABLE
                    | WindowManager.LayoutParams.FLAG_NOT_TOUCHABLE
                    | WindowManager.LayoutParams.FLAG_KEEP_SCREEN_ON;
            params.format = PixelFormat.TRANSLUCENT;
            params.windowAnimations = com.android.internal.R.style.Animation_Toast;
            params.type = WindowManager.LayoutParams.TYPE_TOAST;
            params.setTitle("Toast");
        }

        /**
         * schedule handleShow into the right thread
         */
        public void show() {
            if (localLOGV) Log.v(TAG, "SHOW: " + this);
            mHandler.post(mShow);
        }

        /**
         * schedule handleHide into the right thread
         */
        public void hide() {
            if (localLOGV) Log.v(TAG, "HIDE: " + this);
            mHandler.post(mHide);
        }

        public void handleShow() {
            if (localLOGV) Log.v(TAG, "HANDLE SHOW: " + this + " mView=" + mView
                    + " mNextView=" + mNextView);
            if (mView != mNextView) {
                // remove the old view if necessary
                handleHide();
                mView = mNextView;
                mWM = WindowManagerImpl.getDefault();
                final int gravity = mGravity;
                mParams.gravity = gravity;
                if ((gravity & Gravity.HORIZONTAL_GRAVITY_MASK) == Gravity.FILL_HORIZONTAL) {
                    mParams.horizontalWeight = 1.0f;
                }
                if ((gravity & Gravity.VERTICAL_GRAVITY_MASK) == Gravity.FILL_VERTICAL) {
                    mParams.verticalWeight = 1.0f;
                }
                mParams.x = mX;
                mParams.y = mY;
                mParams.verticalMargin = mVerticalMargin;
                mParams.horizontalMargin = mHorizontalMargin;
                if (mView.getParent() != null) {
                    if (localLOGV) Log.v(TAG, "REMOVE! " + mView + " in " + this);
                    mWM.removeView(mView);
                }
                if (localLOGV) Log.v(TAG, "ADD! " + mView + " in " + this);
                mWM.addView(mView, mParams);
                trySendAccessibilityEvent();
            }
        }

        private void trySendAccessibilityEvent() {
            AccessibilityManager accessibilityManager =
                    AccessibilityManager.getInstance(mView.getContext());
            if (!accessibilityManager.isEnabled()) {
                return;
            }
            // treat toasts as notifications since they are used to
            // announce a transient piece of information to the user
            AccessibilityEvent event = AccessibilityEvent.obtain(
                    AccessibilityEvent.TYPE_NOTIFICATION_STATE_CHANGED);
            event.setClassName(getClass().getName());
            event.setPackageName(mView.getContext().getPackageName());
            mView.dispatchPopulateAccessibilityEvent(event);
            accessibilityManager.sendAccessibilityEvent(event);
        }        

        public void handleHide() {
            if (localLOGV) Log.v(TAG, "HANDLE HIDE: " + this + " mView=" + mView);
            if (mView != null) {
                // note: checking parent() just to make sure the view has
                // been added...  i have seen cases where we get here when
                // the view isn't yet added, so let's try not to crash.
                if (mView.getParent() != null) {
                    if (localLOGV) Log.v(TAG, "REMOVE! " + mView + " in " + this);
                    mWM.removeView(mView);
                }
                mView = null;
            }
        }
    }

重要的还有这个：
Toast中的mService的调用，其实通过IPC调用到了NotificationManagerService

private static INotificationManager sService;

    static private INotificationManager getService() {
        if (sService != null) {
            return sService;
        }
        sService = INotificationManager.Stub.asInterface(ServiceManager.getService("notification"));
        return sService;
    }

在关键的Toast show()方法中:

public void show() {
        if (mNextView == null) {
            throw new RuntimeException("setView must have been called");
        }

        INotificationManager service = getService();
        String pkg = mContext.getPackageName();
        TN tn = mTN;
        tn.mNextView = mNextView;

        try {
            service.enqueueToast(pkg, tn, mDuration);
        } catch (RemoteException e) {
            // Empty
        }
    }

INotificationManager 把消息交给 Notification 去处理 Toast 显示, 消息全部是放在一个集合中，
是这么定义的 private ArrayList mToastQueue;
这就为什么多个Toast会一直逐个显示，直到没有消息为止.

---

我的单例类 T.java

举个自定义Toast的例子：

   LayoutInflater inflater = getLayoutInflater();
   View layout = inflater.inflate(R.layout.custom,
     (ViewGroup) findViewById(R.id.llToast));

   ImageView image = (ImageView) layout
     .findViewById(R.id.tvImageToast);
   image.setImageResource(R.drawable.icon);
   TextView title = (TextView) layout.findViewById(R.id.tvTitleToast);
   title.setText("Attention");
   TextView text = (TextView) layout.findViewById(R.id.tvTextToast);
   text.setText("自定义Toast");

   toast = new Toast(getApplicationContext());
   toast.setGravity(Gravity.RIGHT | Gravity.TOP, 12, 40);
   toast.setDuration(Toast.LENGTH_LONG);
   toast.setView(layout);
   toast.show();

你可以这么做，但我不打算这么做
工具类是一个独立的个体，尽量减少对其他资源的依赖
所以我这里使用代码布局来生成界面

/**
 * Toast工具类
 * 
 * 单例类
 */
public class T {

    private static Toast toast = null;

    private static LinearLayout toastView = null;

    private static final int textId = 2345;

    /**
     * Toast.LENGTH_LONG
     */
    public static void l(String msg) {

        createToast(MyApplication.getInstance());

        toast.setDuration(Toast.LENGTH_LONG);
        setText(msg);
        toast.show();

    }

    /**
     * Toast.LENGTH_SHORT
     */
    public static void s(String msg) {

        createToast(MyApplication.getInstance());

        toast.setDuration(Toast.LENGTH_SHORT);
        setText(msg);
        toast.show();

    }

    private static void setText(String msg) {

        TextView tv = (TextView) toastView.findViewById(textId);
        if (tv != null) {
            tv.setText(msg);
        }
    }

    private static void createToast(Context context) {

        if (toastView == null) {
            toastView = new LinearLayout(context);
            toastView.setOrientation(LinearLayout.VERTICAL);
            LinearLayout.LayoutParams layoutParams = new LinearLayout.LayoutParams(
                    LinearLayout.LayoutParams.WRAP_CONTENT,
                    LinearLayout.LayoutParams.WRAP_CONTENT);
            toastView.setLayoutParams(layoutParams);
            toastView.setBackgroundColor(Color.GRAY);

            TextView textView = new TextView(context);
            textView.setText("");
            textView.setPadding(10, 10, 10, 10);
            textView.setTextColor(Color.WHITE);
            textView.setLayoutParams(layoutParams);
            // 注意设置ID
            textView.setId(textId);

            toastView.addView(textView);
        }

        if (toast == null) {
            toast = new Toast(context);
            toast.setGravity(Gravity.CENTER, 0, 0);
            toast.setView(toastView);
        }
    }
}