解决Android中Toast重复显示的问题

简介

在平时开发中，为了提高用户体验，我们经常会使用Toast来提示一些重要信息，例如“输入正确的用户名”、“密码不能为空”等，但大家都遇到过如下问题：多次点击按钮，界面会匀速弹出Toast，即使切换到其他页面也会弹出，用户体验很不好，这也是本人最近根据测试反馈在项目中优化Toast显示的一点心得记录，下面也针对这种问题，给出解决方案。

分析

根据问题很自然的会想到我们在显示toast之前判断是否已经显示了，没有显示的时候才可以显示。关键点：找到toast的显示状态是什么？
通过源码分析会发现有如下一段

TN(String packageName, @Nullable Looper looper) {
           ....
            mHandler = new Handler(looper, null) {
                @Override
                public void handleMessage(Message msg) {
                    switch (msg.what) {
                        case SHOW: {
                            IBinder token = (IBinder) msg.obj;
                            handleShow(token);
                            break;
                        }
                        case HIDE: {
                            handleHide();
                            // Don't do this in handleHide() because it is also invoked by
                            // handleShow()
                            mNextView = null;
                            break;
                        }
                        case CANCEL: {
                            handleHide();
                            // Don't do this in handleHide() because it is also invoked by
                            // handleShow()
                            mNextView = null;
                            try {
                                getService().cancelToast(mPackageName, TN.this);
                            } catch (RemoteException e) {
                            }
                            break;
                        }
                    }
                }
            };
        }

在手动取消或者隐藏的时候，或者显示时间结束的时候，系统会通过handler发送消息到TN的mHandler中。我们继续分析handleHide()方法

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.removeViewImmediate(mView);
                }


                // Now that we've removed the view it's safe for the server to release
                // the resources.
                try {
                    getService().finishToken(mPackageName, this);
                } catch (RemoteException e) {
                }

                mView = null;
            }
        }

这个方法会将mView视图释放掉，我们的突破口就是这里。在显示之前判断toast的mView是否为null。

解决方法

直接看代码吧

private var toast:Toast?=null
    private fun doToast(message: String? = "", duration: Int = Toast.LENGTH_SHORT, context: Context? = BaseApplication.app) {
        if (toast!=null) {
            if (getTnView(toast!!)!=null) {//正在显示
                return
            }else toast=null
        }
        context?.let {
            toast = Toast.makeText(context, "", duration).apply {
                hook(this)
                setText(message)
                setGravity(Gravity.CENTER, 0, 0)
                show()

            }

        }
    }

    private var sField_TN: Field? = null
    private var sField_TN_Handler: Field? = null

    init {
        try {
            sField_TN = Toast::class.java.getDeclaredField("mTN")
            sField_TN?.isAccessible = true
            sField_TN_Handler = sField_TN?.type?.getDeclaredField("mHandler")
            sField_TN_Handler?.isAccessible = true
        } catch (e: Exception) {
        }
    }

    private fun getTnView(toast: Toast):View?{
        val viewField = sField_TN?.type?.getDeclaredField("mView").also { it?.isAccessible=true }
        val tn = sField_TN?.get(toast)
        return viewField?.get(tn) as? View
    }

    private fun hook(toast: Toast) {
        try {
            val tn = sField_TN?.get(toast)
            val preHandler = sField_TN_Handler?.get(tn) as Handler
            sField_TN_Handler?.set(tn, SafelyHandlerWrapper(preHandler))
        } catch (e: Exception) {
        }

    }
    private class SafelyHandlerWrapper(private val impl: Handler) : Handler() {

        override fun dispatchMessage(msg: Message) {
            try {
                super.dispatchMessage(msg)
            } catch (e: Exception) {
            }
        }

        override fun handleMessage(msg: Message) {
            impl.handleMessage(msg)//需要委托给原Handler执行
        }
    }

getTnView方法通过反射获取当前toast的mView是否是null，不是null表示当前toast正在显示，否则当前toast隐藏或者取消，就可以显示新的toast。