代码是从https://github.com/hastarin/android-udpsender大量借用的,而且他的代码非常通用,我想要一个简单的方法将一个udp数据包发送到一个能解锁车库门的Arduino。
基本上第一页(MainActivity)有一个很大的" Open"按钮和一个小" Set Params"按钮。第二页(Main2Activity)主要是带有批量删除的借用代码,并提供了输入IP地址,端口和解锁代码字的方法。目前有"发送"将已组装的udp数据包发送到客户端的按钮,它按预期工作。
问题是我真的不想定期访问第二页。我需要" sendData" MainActivity中的例程,可以访问存储的值进行处理。
此时,按MainActivity页面上的Send按钮会导致:
java.lang.NullPointerException: Attempt to invoke virtual method 'java.lang.String android.os.Bundle.getString(java.lang.String)' on a null object reference
at com.kke.android.opener.MainActivity.sendData(MainActivity.java:47)
at com.kke.android.opener.MainActivity.onClick(MainActivity.java:30)
我认为该变量值对该页面上的sendData例程不可用。
MainActivity
package com.kke.android.opener;
import android.content.Context;
import android.content.Intent;
import android.net.Uri;
import android.os.Bundle;
import android.app.Activity;
import android.view.View;
import android.widget.Button;
import android.widget.Toast;
public class MainActivity extends Activity implements View.OnClickListener{
private View view;
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
Button btnsend = (Button) findViewById(R.id.buttonSend);
Button btnset = (Button) findViewById(R.id.buttonSet);
btnsend.setOnClickListener(this);
btnset.setOnClickListener(this);
}
@Override
public void onClick(View v) {
switch (v.getId()) {
case R.id.buttonSend:
sendData(v);
break;
case R.id.buttonSet:
editParams(view);
break;
}
}
public void sendData(View view) {
Context context = getApplicationContext();
/**Load global variable from Main2Activity*/
Bundle bundle = getIntent().getExtras();
String host = bundle.getString("host");
String port = bundle.getString("port");
String dataText = bundle.getString("dataText");
//EditText editText = (EditText) findViewById(R.id.editTextIP);
//String host = editText.getText().toString();
if (!host.matches("\\b(?:\\d{1,3}\\.){3}\\d{1,3}\\b")) {
CharSequence text = "Error: Invalid IP Address";
Toast toast = Toast.makeText(context, text, Toast.LENGTH_SHORT);
toast.show();
return;
}
//editText = (EditText) findViewById(R.id.editTextPort);
//String port = editText.getText().toString();
if (!port.matches("^(6553[0-5]|655[0-2]\\d|65[0-4]\\d\\d|6[0-4]\\d{3}|[1-5]\\d{4}|[1-9]\\d{0,3}|0)$")) {
CharSequence text = "Error: Invalid Port Number";
Toast toast = Toast.makeText(context, text, Toast.LENGTH_SHORT);
toast.show();
return;
}
// editText = (EditText) findViewById(R.id.editTextData);
//String dataText = editText.getText().toString();
if (dataText.length() < 1 ) {
CharSequence text = "Error: Text required to send";
Toast toast = Toast.makeText(context, text, Toast.LENGTH_SHORT);
toast.show();
return;
}
String uriString = "udp://" + host + ":" + port + "/";
uriString += Uri.encode(dataText);
Uri uri = Uri.parse(uriString);
Intent intent = new Intent(Intent.ACTION_SENDTO, uri);
intent.addFlags(Intent.FLAG_ACTIVITY_PREVIOUS_IS_TOP);
intent.addCategory(Intent.CATEGORY_DEFAULT);
startActivity(intent);
}
/** Called when the user taps the Set Params button */
public void editParams(View view) {
Intent intent = new Intent(this, Main2Activity.class);
startActivity(intent);
}
}
Main2Activity
package com.kke.android.opener.ui;
import android.app.Activity;
import android.content.Context;
import android.content.Intent;
import android.content.SharedPreferences;
import android.net.Uri;
import android.os.Bundle;
import android.text.InputType;
import android.view.Menu;
import android.view.MenuItem;
import android.view.View;
import android.widget.EditText;
import android.widget.TextView;
import android.widget.Toast;
import android.widget.ToggleButton;
import com.kke.android.opener.R;
public class Main2Activity extends Activity {
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
// Restore preferences
SharedPreferences settings = getPreferences(0);
ToggleButton toggleButton = ((ToggleButton) findViewById(R.id.toggleButton));
boolean checked = settings.getBoolean("toggleChecked", false);
toggleButton.setChecked(checked);
toggleButton.setVisibility(View.GONE);
EditText editText = (EditText) findViewById(R.id.editTextIP);
if (checked) {
editText.setInputType(InputType.TYPE_CLASS_TEXT);
}
editText.setText(settings.getString("host", ""), TextView.BufferType.EDITABLE);
editText = (EditText) findViewById(R.id.editTextPort);
if (checked) {
editText.setInputType(InputType.TYPE_CLASS_TEXT);
}
editText.setText(settings.getString("port", ""), TextView.BufferType.EDITABLE);
editText = (EditText) findViewById(R.id.editTextData);
editText.setText(settings.getString("dataText", ""), TextView.BufferType.EDITABLE);
/** Set up global variable to pass to MainActivity */
Intent intent = new Intent(Main2Activity.this, MainActivity.class);
intent.putExtra("host", "host");
intent.putExtra("port", "port");
intent.putExtra("dataText", "dataText");
startActivity(intent);
}
@Override
public void onPause() {
super.onPause();
// Get current values
EditText editText = (EditText) findViewById(R.id.editTextIP);
String host = editText.getText().toString();
editText = (EditText) findViewById(R.id.editTextPort);
String port = editText.getText().toString();
editText = (EditText) findViewById(R.id.editTextData);
String dataText = editText.getText().toString();
// We need an Editor object to make preference changes.
// All objects are from android.context.Context
SharedPreferences settings = getPreferences(0);
SharedPreferences.Editor editor = settings.edit();
editor.putString("host", host);
editor.putString("port", port);
editor.putString("dataText", dataText);
editor.putBoolean("toggleChecked", ((ToggleButton) findViewById(R.id.toggleButton)).isChecked());
// Commit the edits!
editor.commit();
}
@Override
public boolean onOptionsItemSelected(MenuItem item) {
// Handle item selection
switch (item.getItemId()) {
case R.id.action_send:
this.sendData(null);
return true;
default:
return super.onOptionsItemSelected(item);
}
}
public void sendData(View view) {
Context context = getApplicationContext();
EditText editText = (EditText) findViewById(R.id.editTextIP);
String host = editText.getText().toString();
if (!host.matches("\\b(?:\\d{1,3}\\.){3}\\d{1,3}\\b")) {
CharSequence text = "Error: Invalid IP Address";
Toast toast = Toast.makeText(context, text, Toast.LENGTH_SHORT);
toast.show();
return;
}
editText = (EditText) findViewById(R.id.editTextPort);
String port = editText.getText().toString();
if (!port.matches("^(6553[0-5]|655[0-2]\\d|65[0-4]\\d\\d|6[0-4]\\d{3}|[1-5]\\d{4}|[1-9]\\d{0,3}|0)$")) {
CharSequence text = "Error: Invalid Port Number";
Toast toast = Toast.makeText(context, text, Toast.LENGTH_SHORT);
toast.show();
return;
}
editText = (EditText) findViewById(R.id.editTextData);
String dataText = editText.getText().toString();
if (dataText.length() < 1 ) {
CharSequence text = "Error: Text/Hex required to send";
Toast toast = Toast.makeText(context, text, Toast.LENGTH_SHORT);
toast.show();
return;
}
String uriString = "udp://" + host + ":" + port + "/";
uriString += Uri.encode(dataText);
Uri uri = Uri.parse(uriString);
Intent intent = new Intent(Intent.ACTION_SENDTO, uri);
intent.addFlags(Intent.FLAG_ACTIVITY_PREVIOUS_IS_TOP);
intent.addCategory(Intent.CATEGORY_DEFAULT);
startActivity(intent);
}
public void onToggleClicked(View view) {
boolean on = ((ToggleButton) view).isChecked();
EditText editTextIp = (EditText) findViewById(R.id.editTextIP);
EditText editTextPort = (EditText) findViewById(R.id.editTextPort);
if (on) {
editTextIp.setInputType(InputType.TYPE_CLASS_TEXT);
editTextPort.setInputType(InputType.TYPE_CLASS_TEXT);
} else {
editTextIp.setInputType(InputType.TYPE_CLASS_PHONE);
editTextPort.setInputType(InputType.TYPE_CLASS_PHONE);
}
}
}
所有建议将不胜感激。 请记住我对此很新。
答案 0 :(得分:1)
你的两个活动都有完全相同的布局......这可能令人困惑......
无论如何,当没有额外的东西(刚开始的那个活动)时,你打电话给getIntent().getExtras()
。
您的代码示例
Bundle bundle = getIntent().getExtras(); String host = bundle.getString("host"); String port = bundle.getString("port"); String dataText = bundle.getString("dataText");
你可以简单地这样做
Bundle extras = getIntent().getExtras();
// TODO: declare some variables here
String host, port, text;
if (extras != null) {
// TODO: assign your variables here
String host = extras.getString("host");
String port = extras.getString("port");
String dataText = extras.getString("dataText");
}
然而,如果你因为意图仍然是空的而得不到任何东西,不要感到惊讶
答案 1 :(得分:1)
发生的事情是您的MainActivity可能是从Android启动器启动的,而不是从MainActivity2启动的。
基本上,当您单击“发送”时,您将检查将您带到此处的意图(对此活动)。由于您来自启动程序,因此该意图没有执行该函数所需的数据。请记住,您正在MainActivity2中设置此意图的数据(在您的oncreate方法上,这在此上下文中是一种不好的做法)。
要解决此问题,请转到清单并将MainActivity2作为启动器活动:
<activity android:name="<YOUR_ACTIVITY_TWO_NAME">
<intent-filter>
<action android:name="android.intent.action.MAIN" />
<category android:name="android.intent.category.LAUNCHER" />
</intent-filter>
</activity>
这将确保首先调用您的Activity2,这将链接到MainActivity并发送具有实际数据的意图。