我在开发应用时遇到问题。 我在活动B上有一个按钮，它启动了活动C.我在活动A上有一个textView。我希望每次用户触摸活动B中的按钮时，用一个计数器将活动A的textView增加1。 有人告诉我，我可以使用BroadcastReceiver向活动A发送信息。我试图使用它，但是当我打开活动A时，应用程序崩溃了。 你能帮助我吗？
sendBroadcast（活动B）：
public static String BROADCAST_ACTION = "com.example.appquiz.firstimagelogo.COUNTER";
public void sendBroadcast(View v){
Intent broadcast = new Intent();
broadcast.setAction(BROADCAST_ACTION);
sendBroadcast(broadcast);
}
BroadcastReceiver（活动A）：
//the whole code
package com.example.appquiz;
import android.os.Bundle;
import android.app.ActionBar;
import android.app.Activity;
import android.view.Menu;
import android.view.MenuItem;
import android.view.View;
import android.widget.TextView;
import android.support.v4.app.NavUtils;
import android.annotation.TargetApi;
import android.content.BroadcastReceiver;
import android.content.Context;
import android.content.Intent;
import android.content.IntentFilter;
import android.os.Build;
public class Levels extends Activity {
int counter;
TextView txView ;
public void sendMessage (View view) {
Intent intent = new Intent(this, DisplayMessageActivity.class);
startActivity(intent);
}
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_levels);
// Show the Up button in the action bar.
setupActionBar();
ActionBar actionBar = getActionBar();
actionBar.setIcon(R.drawable.list);
actionBar.setTitle("Levels");
counter=0;
registerReceiver(mReceive , new IntentFilter(
FirstImageLogo.BROADCAST_ACTION));
txView = (TextView)findViewById(R.id.counter1);
}
private BroadcastReceiver mReceive = new BroadcastReceiver() {
@Override
public void onReceive(Context context, Intent intent) {
counter++;
txView.setText(counter + "");
}
};
@Override
public void onBackPressed() {
Intent intent = new Intent (this, MainActivity.class);
startActivity(intent);
return;
}
@Override
public void onResume() {
IntentFilter filter = new IntentFilter();
filter.addAction(FirstImageLogo.BROADCAST_ACTION);
registerReceiver(mReceive, filter);
super.onResume();
}
@Override
public void onPause() {
unregisterReceiver(mReceive);
super.onPause();
}
/**
* Set up the {@link android.app.ActionBar}, if the API is available.
*/
@TargetApi(Build.VERSION_CODES.HONEYCOMB)
private void setupActionBar() {
if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.HONEYCOMB) {
getActionBar().setDisplayHomeAsUpEnabled(true);
}
}
@Override
public boolean onCreateOptionsMenu(Menu menu) {
// Inflate the menu; this adds items to the action bar if it is present.
getMenuInflater().inflate(R.menu.levels, menu);
return true;
}
@Override
public boolean onOptionsItemSelected(MenuItem item) {
switch (item.getItemId()) {
case android.R.id.home:
// This ID represents the Home or Up button. In the case of this
// activity, the Up button is shown. Use NavUtils to allow users
// to navigate up one level in the application structure. For
// more details, see the Navigation pattern on Android Design:
//
// http://developer.android.com/design/patterns/navigation.html#up-vs-back
//
NavUtils.navigateUpFromSameTask(this);
return true;
case R.id.action_settings:
Intent intent = new Intent (this, Settings.class);
startActivity(intent);
}
return super.onOptionsItemSelected(item);
}
}
清单（活动A）：
//codes before
<intent-filter>
<action android:name="com.example.appquiz.firstimagelogo.COUNTER"></action>
</intent-filter>
谢谢：）
编辑：当它崩溃时，这就是日志猫：
01-29 15:26:16.190: D/OpenGLRenderer(22554): Enabling debug mode 0
01-29 15:26:17.210: D/dalvikvm(22554): GC_FOR_ALLOC freed 110K, 1% free 17784K/17932K, paused 10ms, total 10ms
01-29 15:26:18.420: D/AndroidRuntime(22554): Shutting down VM
01-29 15:26:18.420: W/dalvikvm(22554): threadid=1: thread exiting with uncaught exception (group=0x41c22ba8)
01-29 15:26:18.430: E/AndroidRuntime(22554): FATAL EXCEPTION: main
01-29 15:26:18.430: E/AndroidRuntime(22554): Process: com.example.appquiz, PID: 22554
01-29 15:26:18.430: E/AndroidRuntime(22554): java.lang.RuntimeException: Unable to instantiate activity ComponentInfo{com.example.appquiz/com.example.appquiz.Levels}: java.lang.NullPointerException
01-29 15:26:18.430: E/AndroidRuntime(22554): at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2121)
01-29 15:26:18.430: E/AndroidRuntime(22554): at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2245)
01-29 15:26:18.430: E/AndroidRuntime(22554): at android.app.ActivityThread.access$800(ActivityThread.java:135)
01-29 15:26:18.430: E/AndroidRuntime(22554): at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1196)
01-29 15:26:18.430: E/AndroidRuntime(22554): at android.os.Handler.dispatchMessage(Handler.java:102)
01-29 15:26:18.430: E/AndroidRuntime(22554): at android.os.Looper.loop(Looper.java:136)
01-29 15:26:18.430: E/AndroidRuntime(22554): at android.app.ActivityThread.main(ActivityThread.java:5017)
01-29 15:26:18.430: E/AndroidRuntime(22554): at java.lang.reflect.Method.invokeNative(Native Method)
01-29 15:26:18.430: E/AndroidRuntime(22554): at java.lang.reflect.Method.invoke(Method.java:515)
01-29 15:26:18.430: E/AndroidRuntime(22554): at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:779)
01-29 15:26:18.430: E/AndroidRuntime(22554): at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:595)
01-29 15:26:18.430: E/AndroidRuntime(22554): at dalvik.system.NativeStart.main(Native Method)
01-29 15:26:18.430: E/AndroidRuntime(22554): Caused by: java.lang.NullPointerException
01-29 15:26:18.430: E/AndroidRuntime(22554): at android.app.Activity.findViewById(Activity.java:1884)
01-29 15:26:18.430: E/AndroidRuntime(22554): at com.example.appquiz.Levels.<init>(Levels.java:21)
01-29 15:26:18.430: E/AndroidRuntime(22554): at java.lang.Class.newInstanceImpl(Native Method)
01-29 15:26:18.430: E/AndroidRuntime(22554): at java.lang.Class.newInstance(Class.java:1208)
01-29 15:26:18.430: E/AndroidRuntime(22554): at android.app.Instrumentation.newActivity(Instrumentation.java:1061)
01-29 15:26:18.430: E/AndroidRuntime(22554): at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2112)
01-29 15:26:18.430: E/AndroidRuntime(22554): ... 11 more
答案 0 :(得分：2)
好像你没有注册接收器...这是你注册的方式
registerReceiver(mReceive , new IntentFilter(
ActivityA or whatever the name of the activity is.BROADCAST_ACTION));
答案 1 :(得分：1)
您可以使用SharedPreferences。每次按下按钮，增加计数器并写入首选项，然后在ActivityA中读取该值并设置TextView，例如：
按下按钮时：
SharedPreferences prefs = getSharedPreferences("prefs", Context.MODE_PRIVATE);
SharedPreferenes.Editor editor = prefs.edit();
int counter = prefs.getInt("counter", 0);
counter++;
editor.putInt("counter", counter);
editor.commit();
在ActivityA中，读取计数器的值并设置TextView：
SharedPreferences prefs = getSharedPreferences("prefs", Context.MODE_PRIVATE);
int counter = prefs.getInt("counter", 0);
someTextView.setText("Counter is: " + counter);