子執行緒Handler sendMessage 報錯 Attempt to invoke virtual method '
阿新 • • 發佈：2018-12-21
03-17 08:10:18.760 16029-16029/tech.androidstudio.tulingdemo E/AndroidRuntime: FATAL EXCEPTION: main03-17 08:10:18.760 16029-16029/tech.androidstudio.tulingdemo E/AndroidRuntime: Process: tech.androidstudio.tulingdemo, PID: 1602903-17 08:10:18.760 16029-16029/tech.androidstudio.tulingdemo E/AndroidRuntime: java.lang.IllegalStateException: Could not execute method for android:onClick03-17 08:10:18.760 16029-16029/tech.androidstudio.tulingdemo E/AndroidRuntime: at android.support.v7.app.AppCompatViewInflater$DeclaredOnClickListener.onClick(AppCompatViewInflater.java:275)03-17 08:10:18.760 16029-16029/tech.androidstudio.tulingdemo E/AndroidRuntime: at android.view.View.performClick(View.java:4761)03-17 08:10:18.760 16029-16029/tech.androidstudio.tulingdemo E/AndroidRuntime: at android.view.View$PerformClick.run(View.java:19767)03-17 08:10:18.760 16029-16029/tech.androidstudio.tulingdemo E/AndroidRuntime: at android.os.Handler.handleCallback(Handler.java:739)03-17 08:10:18.760 16029-16029/tech.androidstudio.tulingdemo E/AndroidRuntime: at android.os.Handler.dispatchMessage(Handler.java:95)03-17 08:10:18.760 16029-16029/tech.androidstudio.tulingdemo E/AndroidRuntime: at android.os.Looper.loop(Looper.java:135)03-17 08:10:18.760 16029-16029/tech.androidstudio.tulingdemo E/AndroidRuntime: at android.app.ActivityThread.main(ActivityThread.java:5310)03-17 08:10:18.760 16029-16029/tech.androidstudio.tulingdemo E/AndroidRuntime: at java.lang.reflect.Method.invoke(Native Method)03-17 08:10:18.760 16029-16029/tech.androidstudio.tulingdemo E/AndroidRuntime: at java.lang.reflect.Method.invoke(Method.java:372)03-17 08:10:18.760 16029-16029/tech.androidstudio.tulingdemo E/AndroidRuntime: at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:901)03-17 08:10:18.760 16029-16029/tech.androidstudio.tulingdemo E/AndroidRuntime: at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:696)03-17 08:10:18.760 16029-16029/tech.androidstudio.tulingdemo E/AndroidRuntime: Caused by: java.lang.reflect.InvocationTargetException03-17 08:10:18.760 16029-16029/tech.androidstudio.tulingdemo E/AndroidRuntime: at java.lang.reflect.Method.invoke(Native Method)03-17 08:10:18.760 16029-16029/tech.androidstudio.tulingdemo E/AndroidRuntime: at java.lang.reflect.Method.invoke(Method.java:372)03-17 08:10:18.760 16029-16029/tech.androidstudio.tulingdemo E/AndroidRuntime: at android.support.v7.app.AppCompatViewInflater$DeclaredOnClickListener.onClick(AppCompatViewInflater.java:270)03-17 08:10:18.760 16029-16029/tech.androidstudio.tulingdemo E/AndroidRuntime: at android.view.View.performClick(View.java:4761) 03-17 08:10:18.760 16029-16029/tech.androidstudio.tulingdemo E/AndroidRuntime: at android.view.View$PerformClick.run(View.java:19767) 03-17 08:10:18.760 16029-16029/tech.androidstudio.tulingdemo E/AndroidRuntime: at android.os.Handler.handleCallback(Handler.java:739) 03-17 08:10:18.760 16029-16029/tech.androidstudio.tulingdemo E/AndroidRuntime: at android.os.Handler.dispatchMessage(Handler.java:95) 03-17 08:10:18.760 16029-16029/tech.androidstudio.tulingdemo E/AndroidRuntime: at android.os.Looper.loop(Looper.java:135) 03-17 08:10:18.760 16029-16029/tech.androidstudio.tulingdemo E/AndroidRuntime: at android.app.ActivityThread.main(ActivityThread.java:5310) 03-17 08:10:18.760 16029-16029/tech.androidstudio.tulingdemo E/AndroidRuntime: at java.lang.reflect.Method.invoke(Native Method) 03-17 08:10:18.760 16029-16029/tech.androidstudio.tulingdemo E/AndroidRuntime: at java.lang.reflect.Method.invoke(Method.java:372) 03-17 08:10:18.760 16029-16029/tech.androidstudio.tulingdemo E/AndroidRuntime: at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:901) 03-17 08:10:18.760 16029-16029/tech.androidstudio.tulingdemo E/AndroidRuntime: at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:696) 03-17 08:10:18.760 16029-16029/tech.androidstudio.tulingdemo E/AndroidRuntime: Caused by: java.lang.NullPointerException: Attempt to invoke virtual method 'boolean android.os.Handler.sendMessage(android.os.Message)' on a null object reference03-17 08:10:18.760 16029-16029/tech.androidstudio.tulingdemo E/AndroidRuntime: at tech.androidstudio.tulingdemo.MainActivity.btnSendMessage(MainActivity.java:65)03-17 08:10:18.760 16029-16029/tech.androidstudio.tulingdemo E/AndroidRuntime: at java.lang.reflect.Method.invoke(Native Method) 03-17 08:10:18.760 16029-16029/tech.androidstudio.tulingdemo E/AndroidRuntime: at java.lang.reflect.Method.invoke(Method.java:372) 03-17 08:10:18.760 16029-16029/tech.androidstudio.tulingdemo E/AndroidRuntime: at android.support.v7.app.AppCompatViewInflater$DeclaredOnClickListener.onClick(AppCompatViewInflater.java:270) 03-17 08:10:18.760 16029-16029/tech.androidstudio.tulingdemo E/AndroidRuntime: at android.view.View.performClick(View.java:4761) 03-17 08:10:18.760 16029-16029/tech.androidstudio.tulingdemo E/AndroidRuntime: at android.view.View$PerformClick.run(View.java:19767) 03-17 08:10:18.760 16029-16029/tech.androidstudio.tulingdemo E/AndroidRuntime: at android.os.Handler.handleCallback(Handler.java:739) 03-17 08:10:18.760 16029-16029/tech.androidstudio.tulingdemo E/AndroidRuntime: at android.os.Handler.dispatchMessage(Handler.java:95) 03-17 08:10:18.760 16029-16029/tech.androidstudio.tulingdemo E/AndroidRuntime: at android.os.Looper.loop(Looper.java:135) 03-17 08:10:18.760 16029-16029/tech.androidstudio.tulingdemo E/AndroidRuntime: at android.app.ActivityThread.main(ActivityThread.java:5310) 03-17 08:10:18.760 16029-16029/tech.androidstudio.tulingdemo E/AndroidRuntime: at java.lang.reflect.Method.invoke(Native Method) 03-17 08:10:18.760 16029-16029/tech.androidstudio.tulingdemo E/AndroidRuntime: at java.lang.reflect.Method.invoke(Method.java:372) 03-17 08:10:18.760 16029-16029/tech.androidstudio.tulingdemo E/AndroidRuntime: at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:901)
03-17 08:10:18.760 16029-16029/tech.androidstudio.tulingdemo E/AndroidRuntime: at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:696)
原因分析 ：
子執行緒handler 報錯，是因為沒有啟動子執行緒就開始使用了。
解決辦法：
在onCreate方法中啟動Thread，千萬別忘了Thread裡面的this 引數，不然還會報錯。
Thread thread = new Thread(this); thread.start();public class MainActivity extends AppCompatActivity implements Runnable {private EditText mEditText; private ListView mListView; private List<String>mData; private ListViewAdapter mAdapter; private Handler subHandler; private Handler mainHandler; private final int MAIN_HANDLER_ADD=98; private final int SUB_HANDLER_ADD=998; private final int SUB_HANDLER_EXIT=199; @Overrideprotected void onCreate(Bundle savedInstanceState) {super.onCreate(savedInstanceState); setContentView(R.layout.activity_main); mEditText=(EditText)findViewById(R.id.editText); mListView=(ListView)findViewById(R.id.listView); mData = new ArrayList<>(); mAdapter = new ListViewAdapter(mData,this); mListView.setAdapter(mAdapter); mainHandler = new Handler(){ @Overridepublic void handleMessage(Message msg) { super.handleMessage(msg); int what = msg.what; switch (what){ case MAIN_HANDLER_ADD: String msg_reply = (String)msg.obj; mData.add(msg_reply); mAdapter.notifyDataSetChanged(); break; } } }; //千萬別忘了啟動子執行緒，不然會報錯//Attempt to invoke virtual method 'boolean android.os.Handler.sendMessage(android.os.Message)' on a null object referenceThread thread = new Thread(this); thread.start(); } public void btnSendMessage(View view) { String message_send = mEditText.getText().toString(); if(message_send!=null){ mData.add(message_send); mAdapter.notifyDataSetChanged(); //將要傳送的訊息傳送給子執行緒,(給子執行緒的handler)，因為耗時操作不能在主執行緒進行// 然後子執行緒請求資料再返回給主執行緒（主執行緒的 handler），因為 子執行緒不能修改介面的UIMessage message = Message.obtain(); message.what=SUB_HANDLER_ADD; message.obj=message_send; subHandler.sendMessage(message);//之前報錯的位置是這一步 } } @Overridepublic void run() { //繫結 當前執行緒的LooperLooper.prepare(); subHandler= new Handler(){ @Overridepublic void handleMessage(Message msg) { super.handleMessage(msg); int what = msg.what; switch (what){ case SUB_HANDLER_ADD: //獲取傳送的訊息，然後通過HttpUtils來發送，並且得到返回值，//把這個返回值 再給主執行緒的 handler來處理。//先寫一個模擬資料 ，例如"收到了"傳送給主執行緒。Message message = Message.obtain(); message.what=MAIN_HANDLER_ADD; message.obj="收到了"; mainHandler.sendMessage(message); break; case SUB_HANDLER_EXIT: //在onDestroy裡面停止這個LooperLooper looper = Looper.myLooper(); looper.quit(); break; } } }; //不停的迴圈 ，就像是while一樣。Looper.loop(); }}