作为Android的新手，我正在开发一款应该将信息从一个活动传递到另一个活动的Android应用。在第一个活动中以正确的方式检索信息 - 它记录到日志cat中 - 但是在第二个活动中没有收到，因为通过意图传递的值返回null。这就是我被困住的地方，以及任何提示或帮助将非常感激。
第一个Java类：
package de.die_web_agenten.www.runinstant;
import android.app.Activity;
import android.app.AlertDialog;
import android.content.ActivityNotFoundException;
import android.content.DialogInterface;
import android.content.Intent;
import android.database.Cursor;
import android.database.sqlite.SQLiteDatabase;
import android.net.Uri;
import android.os.Bundle;
import android.util.Log;
import android.view.View;
import android.widget.ListAdapter;
import android.widget.SimpleCursorAdapter;
import android.widget.Toast;
import de.die_web_agenten.www.runinstant.db.TaskContract;
import de.die_web_agenten.www.runinstant.db.TaskDBHelper;
public class AndroidBarcodeQrExample extends Activity {
/** Called when the activity is first created. */
static final String ACTION_SCAN = "com.google.zxing.client.android.SCAN";
private ListAdapter listAdapter;
private TaskDBHelper helper;
@Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_barcode);
}
public void scanBar(View v) {
try {
Intent intent = new Intent(ACTION_SCAN);
intent.putExtra("SCAN_MODE", "PRODUCT_MODE");
startActivityForResult(intent, 0);
} catch (ActivityNotFoundException anfe) {
showDialog(AndroidBarcodeQrExample.this, "No Scanner Found", "Download a scanner code activity?", "Yes", "No").show();
}
}
public void scanQR(View v) {
try {
Intent intent = new Intent(ACTION_SCAN);
intent.putExtra("SCAN_MODE", "QR_CODE_MODE");
startActivityForResult(intent, 0);
} catch (ActivityNotFoundException anfe) {
showDialog(AndroidBarcodeQrExample.this, "No Scanner Found", "Download a scanner code activity?", "Yes", "No").show();
}
}
private static AlertDialog showDialog(final Activity act, CharSequence title, CharSequence message, CharSequence buttonYes, CharSequence buttonNo) {
AlertDialog.Builder downloadDialog = new AlertDialog.Builder(act);
downloadDialog.setTitle(title);
downloadDialog.setMessage(message);
downloadDialog.setPositiveButton(buttonYes, new DialogInterface.OnClickListener() {
public void onClick(DialogInterface dialogInterface, int i) {
Uri uri = Uri.parse("market://search?q=pname:" + "com.google.zxing.client.android");
Intent intent = new Intent(Intent.ACTION_VIEW, uri);
try {
act.startActivity(intent);
} catch (ActivityNotFoundException anfe) {
}
}
});
downloadDialog.setNegativeButton(buttonNo, new DialogInterface.OnClickListener() {
public void onClick(DialogInterface dialogInterface, int i) {
}
});
return downloadDialog.show();
}
private void updateUI() {
helper = new TaskDBHelper(AndroidBarcodeQrExample.this);
SQLiteDatabase sqlDB = helper.getReadableDatabase();
Cursor cursor = sqlDB.query(TaskContract.TABLE,
new String[]{ TaskContract.Columns.SCAN_RESULT, TaskContract.Columns.SCAN_FORMAT,TaskContract.Columns._id,
TaskContract.Columns.DATE},
null, null, null, null, null
);
listAdapter = new SimpleCursorAdapter(
this,
R.layout.task_view,
cursor,
new String[]{TaskContract.Columns.SCAN_FORMAT, TaskContract.Columns.SCAN_RESULT, TaskContract.Columns._id},
new int[]{R.id.taskTextView},
0
);
this.setListAdapter(listAdapter);
}
public void onActivityResult(int requestCode, int resultCode, Intent intent) {
if (requestCode == 0) {
if (resultCode == RESULT_OK) {
String contents = intent.getStringExtra("SCAN_RESULT");
String format = intent.getStringExtra("SCAN_RESULT_FORMAT");
Toast toast = Toast.makeText(this, "Content:" + contents + " Format:" + format, Toast.LENGTH_LONG);
toast.show();
/*Intent SecondIntent = new Intent(AndroidBarcodeQrExample.this, SecondListActivity.class);
SecondIntent.putExtra("SCAN_RESULT", contents);
startActivity(SecondIntent);*/
Intent SecondIntent = new Intent(getBaseContext(), SecondListActivity.class);
intent.putExtra("SCAN_RESULT", contents);
intent.putExtra("SCAN_RESULT_FORMAT", format);
startActivity(SecondIntent);
Log.d("ADebugTag", "Value: " + (contents));
Log.d("BDebugTag", "Value: " + (format));
//updateUI();
//Context context = getApplicationContext();
//CharSequence text = "Informationen erfolgreich gespeichert!";
//int duration = Toast.LENGTH_SHORT;
//Toast toast = Toast.makeText(context, text, duration);
}
}
}
public void setListAdapter(ListAdapter listAdapter) {
this.listAdapter = listAdapter;
}
}
这是第二项活动，不会以正确的方式检索信息：
package de.die_web_agenten.www.runinstant;
import android.app.ListActivity;
import android.content.Intent;
import android.database.Cursor;
import android.database.sqlite.SQLiteDatabase;
import android.os.Bundle;
import android.os.Handler;
import android.os.Message;
import android.util.Log;
import android.widget.ListAdapter;
import android.widget.SimpleCursorAdapter;
import java.util.ArrayList;
import de.die_web_agenten.www.runinstant.db.TaskContract;
import de.die_web_agenten.www.runinstant.db.TaskDBHelper;
public class SecondListActivity extends ListActivity {
// declare class variables
private ArrayList<Item> m_parts = new ArrayList<Item>();
private Runnable viewParts;
private ItemAdapter m_adapter;
private ListAdapter listAdapter;
private TaskDBHelper helper;
/** Called when the activity is first created. */
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.main);
// instantiate our ItemAdapter class
m_adapter = new ItemAdapter(this, R.layout.list_item, m_parts);
setListAdapter(m_adapter);
// here we are defining our runnable thread.
viewParts = new Runnable(){
public void run(){
handler.sendEmptyMessage(0);
}
};
// here we call the thread we just defined - it is sent to the handler below.
Thread thread = new Thread(null, viewParts, "MagentoBackground");
thread.start();
}
private void updateUI() {
helper = new TaskDBHelper(SecondListActivity.this);
SQLiteDatabase sqlDB = helper.getReadableDatabase();
Cursor cursor = sqlDB.query(TaskContract.TABLE,
new String[]{TaskContract.Columns.SCAN_RESULT, TaskContract.Columns.SCAN_FORMAT,
TaskContract.Columns.DATE, TaskContract.Columns._id },
null, null, null, null, null
);
listAdapter = new SimpleCursorAdapter(
this,
R.layout.task_view,
cursor,
new String[]{TaskContract.Columns.SCAN_FORMAT, TaskContract.Columns.SCAN_RESULT, TaskContract.Columns._id},
new int[]{R.id.taskTextView},
0
);
this.setListAdapter(listAdapter);
}
private Handler handler = new Handler()
{
public void handleMessage(Message msg)
{
// create some objects
// here is where you could also request data from a server
// and then create objects from that data.
/*String sql = String.format("DELETE FROM %s WHERE %s = '%s'",
TaskContract.TABLE,
TaskContract.Columns.SCAN_FORMAT,
TaskContract.Columns.SCAN_RESULT
);
helper = new TaskDBHelper(SecondListActivity.this);
SQLiteDatabase sqlDB = helper.getWritableDatabase();
sqlDB.execSQL(sql);*/
Intent SecondIntent = getIntent();
String contents = SecondIntent.getStringExtra("SCAN_RESULT");
//String contents = SecondIntent.getStringExtra("SCAN_RESULT", contents);
String format = SecondIntent.getStringExtra("SCAN_RESULT_FORMAT");
m_parts.add(new Item(contents, format, 0));
m_parts.add(new Item("MyItemName #2", "This is item #2", 0));
Log.d("CDebugTag", "Value: " + (contents));
//Log.d("DDebugTag", "Value: " + (format));
/*m_parts.add(new Item("MyItemName", "This is item #3", 0));
m_parts.add(new Item("MyItemName #2", "This is item #4", 0));
m_parts.add(new Item("MyItemName", "This is item #5", 0));
m_parts.add(new Item("MyItemName #2", "This is item #6", 0));
m_parts.add(new Item("MyItemName", "This is item #7", 0));
m_parts.add(new Item("MyItemName #2", "This is item #8", 0));
m_parts.add(new Item("MyItemName", "This is item #9", 0));
m_parts.add(new Item("MyItemName #2", "This is item #10", 0));*/
m_adapter = new ItemAdapter(SecondListActivity.this, R.layout.list_item, m_parts);
// display the list.
setListAdapter(m_adapter);
//updateUI();
}
};
}
这两项活动都在应用的Android清单中注册：
<activity
android:name=".MapsActivity"
android:label="@string/title_activity_maps" />
<activity
android:name=".ResultsActivity"
android:label="@string/title_activity_results"
android:theme="@style/AppTheme.NoActionBar" />
<activity
android:name=".TrainingActivity"
android:label="@string/title_activity_training"
android:theme="@style/AppTheme.NoActionBar" />
<activity
android:name=".SecondListActivity"
android:label="@string/title_activity_list"
android:theme="@style/AppTheme.NoActionBar" />
<activity
android:name=".AndroidBarcodeQrExample"
android:label="@string/title_barcode_class"
android:theme="@style/AppTheme.NoActionBar" />
我被困在这里，因为我不明白为什么信息不会通过第二个活动中的意图进行检索，因为Android应该发送意图而我在日志猫中没有任何错误。任何提示或信息都非常受欢迎，谢谢。
答案 0 :(得分：2)
您的处理程序对象需要一个Callback参数
Handler handler = new Handler(new Handler.Callback() {
@Override
public boolean handleMessage(Message message) {
smth();
...
return messageHandled;
}
});
你可以使用Handler.Callback接口或实现你自己的子类，这比第一个选项更难，所以我建议使用上面的实现。我试过了，它确实有用。
编辑1：返回是否处理了消息，确保处理程序不会处理多次消息。