Message m=handler.obtainMessage();出现程序闪退

Question

package com.example.administrator.a6_666;

import android.os.Handler;
import android.os.Message;
import android.support.v7.app.AppCompatActivity;
import android.os.Bundle;
import android.widget.TextView;

import java.util.Random;

public class MainActivity extends AppCompatActivity implements Runnable{
private TextView tv;
private Handler handler;

@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
tv=(TextView)findViewById(R.id.txt);
Thread t=new Thread(this);
t.start();
handler=new Handler(){
@Override
public void handleMessage(Message msg){
if(msg.what==0x101){
tv.setText(msg.obj.toString());
}
super.handleMessage(msg);
}
};
}
@Override
public void run(){
String value="";
int max=99999;
int min=11111;
while(!Thread.currentThread().isInterrupted()){
value=String.valueOf(new Random().nextInt(max)%(max-min+1)+min);

        Message m=handler.obtainMessage();//显示这句出现错误

m.obj=value;
m.what=0x101;
handler.sendMessage(m);
try{
Thread.sleep(1000);
}catch(InterruptedException e){
e.printStackTrace();
}
}
}
以下是错误
com.example.administrator.a6_666 E/AndroidRuntime: FATAL EXCEPTION: Thread-1626
Process: com.example.administrator.a6_666, PID: 10217
java.lang.NullPointerException: Attempt to invoke virtual method 'android.os.Message android.os.Handler.obtainMessage()' on a null object reference
at com.example.administrator.a6_666.MainActivity.run(MainActivity.java:41)
at java.lang.Thread.run(Thread.java:818)

Answer 1

Thread t开始run的时候handler还没有被赋值，handler是null的。
需要将handler=new Handler(){ ...};这部分代码放到t.start()之前。