Android 7.1.1 Toast引起的Crash

背景

最近一直做国际化项目，用户使用的手机都是android中低档手机，出现的问题也比较奇葩，最近项目刚上线就遇到了一个crash

android.view.WindowManager$BadTokenException: Unable to add window -- token android.os.BinderProxy@bf0c2d7 is not valid; is your activity running?    at android.view.ViewRootImpl.setView(ViewRootImpl.java:797)    at android.view.WindowManagerGlobal.addView(WindowManagerGlobal.java:351)    at android.view.WindowManagerImpl.addView(WindowManagerImpl.java:93)    at android.widget.Toast$TN.handleShow(Toast.java:465)    at android.widget.Toast$TN$2.handleMessage(Toast.java:347)    at android.os.Handler.dispatchMessage(Handler.java:110)    at android.os.Looper.loop(Looper.java:203)    at android.app.ActivityThread.main(ActivityThread.java:6337)    at java.lang.reflect.Method.invoke(Native Method)    at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:1084)

初步分析

最开始我以为是dialog或者popwindow引起的问题，我还找相关同事排查了一下，发现不是，通过log堆栈分析是Toast引起的问题，这个奇怪了，这个项目的代码之前一直在国内运行，一直没有发现过这个问题，如果是项目中Toast使用问题应该早就发现了？？

搜索相关资料

在网上找了写相关资料，也有不少网友遇到类似的问题，问题都是集中在Android7.1.1和Android7.1.2机型上，出问题的机型正好是Android7.1.1手机！先看看到底是什么原因引起的吧

Android7.1.1出现问题的原因

先来看看前辈的解答吧

答案.png

总结一下，这个问题可以算是android 系统为了优化系统，才引起了bug，好在8.0的系统上已经发现这个问题已经try-catch修复了，最起码不导致崩溃了
截取了一段Toast的源代码（Android8.0 的源码），已经处理了

  public void handleShow(IBinder windowToken) {            if (localLOGV) Log.v(TAG, "HANDLE SHOW: " + this + " mView=" + mView                    + " mNextView=" + mNextView);            // If a cancel/hide is pending - no need to show - at this point            // the window token is already invalid and no need to do any work.            if (mHandler.hasMessages(CANCEL) || mHandler.hasMessages(HIDE)) {                return;            }            if (mView != mNextView) {                // remove the old view if necessary                handleHide();                mView = mNextView;                Context context = mView.getContext().getApplicationContext();                String packageName = mView.getContext().getOpPackageName();                if (context == null) {                    context = mView.getContext();                }                mWM = (WindowManager)context.getSystemService(Context.WINDOW_SERVICE);                // We can resolve the Gravity here by using the Locale for getting                // the layout direction                final Configuration config = mView.getContext().getResources().getConfiguration();                final int gravity = Gravity.getAbsoluteGravity(mGravity, config.getLayoutDirection());                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;                mParams.packageName = packageName;                mParams.hideTimeoutMilliseconds = mDuration ==                    Toast.LENGTH_LONG ? LONG_DURATION_TIMEOUT : SHORT_DURATION_TIMEOUT;                mParams.token = windowToken;                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);                // Since the notification manager service cancels the token right                // after it notifies us to cancel the toast there is an inherent                // race and we may attempt to add a window after the token has been                // invalidated. Let us hedge against that.                try {                    mWM.addView(mView, mParams);                    trySendAccessibilityEvent();                } catch (WindowManager.BadTokenException e) {                    /* ignore */                    //关键的地方，已经catch住了                }            }        }

如果要从根本上解决这类问题还是比较难的，因为要排查系统中哪些地方导致了主线程阻塞住了，但是如果直接解决这个崩溃问题还是比较简单的

解决方案

网上有一个解决这个问题的[开源库]https://github.com/drakeet/ToastCompat)

思路：

So I created this library, and replace the base Context to a SafeToastContext, it will hook the WindowManagerWrapper.addView(view, params) method and fix the exception.

实际上就是Hook住了系统WindowManager的addview方法，对这个方式try-catch处理了

文件分析：主要就三个文件

文件目录.png

使用方式

import android.os.Bundle;import android.support.v7.app.AppCompatActivity;import android.util.Log;import android.widget.Toast;import me.drakeet.support.toast.ToastCompat;public class MainActivity extends AppCompatActivity {  @Override  protected void onCreate(Bundle savedInstanceState) {    super.onCreate(savedInstanceState);    setContentView(R.layout.activity_main);    ToastCompat.makeText(this, "hello", Toast.LENGTH_SHORT)        .setBadTokenListener(toast -> {          Log.e("failed toast", "hello");        }).show();  }}

对弹出Toast地方，都使用统一的ToastCompat方式，我们看一下ToastCompat是什么吧？

ToastCompat就是对Toast的代理也可以称之为委托，先看一下关键方法makeText

  public static ToastCompat makeText(Context context, CharSequence text, int duration) {    // We cannot pass the SafeToastContext to Toast.makeText() because    // the View will unwrap the base context and we are in vain.    @SuppressLint("ShowToast")    Toast toast = Toast.makeText(context, text, duration);    setContextCompat(toast.getView(), new SafeToastContext(context, toast));    return new ToastCompat(context, toast);  }

首先创建了一个Toast对象，然后又调用了setContextCompat方法

 private static void setContextCompat(@NonNull View view, @NonNull Context context) {    if (Build.VERSION.SDK_INT == 25) {      try {        Field field = View.class.getDeclaredField("mContext");        field.setAccessible(true);        field.set(view, context);      } catch (Throwable throwable) {        throwable.printStackTrace();      }    }  }

把ToastView context 给替换了

final class SafeToastContext extends ContextWrapper {  private @NonNull Toast toast;  private @Nullable BadTokenListener badTokenListener;  SafeToastContext(@NonNull Context base, @NonNull Toast toast) {    super(base);    this.toast = toast;  }  @Override  public Context getApplicationContext() {    return new ApplicationContextWrapper(getBaseContext().getApplicationContext());  }  public void setBadTokenListener(@NonNull BadTokenListener badTokenListener) {    this.badTokenListener = badTokenListener;  }

关键的是getApplicationContext 这个方法

  private final class ApplicationContextWrapper extends ContextWrapper {    private ApplicationContextWrapper(@NonNull Context base) {      super(base);    }    @Override    public Object getSystemService(@NonNull String name) {      if (Context.WINDOW_SERVICE.equals(name)) {        // noinspection ConstantConditions        return new WindowManagerWrapper((WindowManager) getBaseContext().getSystemService(name));      }      return super.getSystemService(name);    }  }

实际上在获取系统中WindowManager的时候，是获取了我们包装类的
WindowManagerWrapper，在这个类中我们对addView 增加了try-catch的操作

private final class WindowManagerWrapper implements WindowManager {    private static final String TAG = "WindowManagerWrapper";    private final @NonNull WindowManager base;    private WindowManagerWrapper(@NonNull WindowManager base) {      this.base = base;    }    @Override    public Display getDefaultDisplay() {      return base.getDefaultDisplay();    }    @Override    public void removeViewImmediate(View view) {      base.removeViewImmediate(view);    }    @Override    public void addView(View view, ViewGroup.LayoutParams params) {      try {        Log.d(TAG, "WindowManager's addView(view, params) has been hooked.");        base.addView(view, params);      } catch (BadTokenException e) {        Log.i(TAG, e.getMessage());        if (badTokenListener != null) {          badTokenListener.onBadTokenCaught(toast);        }      } catch (Throwable throwable) {        Log.e(TAG, "[addView]", throwable);      }    }    @Override    public void updateViewLayout(View view, ViewGroup.LayoutParams params) {      base.updateViewLayout(view, params);    }    @Override    public void removeView(View view) {      base.removeView(view);    }  }

总结：代码并不复杂，逻辑比较清晰，实现的思路也是比较有趣的

疑问：

Toast的实现原理是什么呢？
ContextWrapper 是什么呢？
ContextWrapper 中getApplicationContext 返回的是什么呢

为什么会有这些疑问，一般对疑难的crash问题我都喜欢刨根问底，探究问题根源对问题的执着会让你在过程中收获很多问题，以上问题就是我在专研这类问题的时候遇到的相关知识,有写知识之前都看过但是随着时间的流逝也都不记得了

引用

大家有没有遇到过只在 Android 7.1 机型上报告的由Toast引起的BadTokenException错误？

github 上解决方案

Toast与Snackbar的那点事

Android7.1.1Toast崩溃解决方案

Android(安卓)7.1.1 Toast引起的Crash