我最近开始上大学的第一个应用程序,作为我的应用程序的一部分,我想使用this guide.
访问手机的联系人在指南中,onActivityResult看起来像这样:
@Override
protected void onActivityResult(int requestCode, int resultCode, Intent data) {
// Check which request it is that we're responding to
if (requestCode == PICK_CONTACT_REQUEST) {
// Make sure the request was successful
if (resultCode == RESULT_OK) {
// Get the URI that points to the selected contact
Uri contactUri = data.getData();
// We only need the NUMBER column, because there will be only one row in the result
String[] projection = {Phone.NUMBER};
// Perform the query on the contact to get the NUMBER column
// We don't need a selection or sort order (there's only one result for the given URI)
// CAUTION: The query() method should be called from a separate thread to avoid blocking
// your app's UI thread. (For simplicity of the sample, this code doesn't do that.)
// Consider using CursorLoader to perform the query.
Cursor cursor = getContentResolver()
.query(contactUri, projection, null, null, null);
cursor.moveToFirst();
// Retrieve the phone number from the NUMBER column
int column = cursor.getColumnIndex(Phone.NUMBER);
String number = cursor.getString(column);
// Do something with the phone number...
}
}
}
它说我应该使用一个线程或CursorLoader来进行查询,但到目前为止我无法为此找到一个好的解决方案。如果我将查询方法放在一个线程中,那么我就无法从中访问数据:
Runnable r = new Runnable() {
@Override
public void run() {
Cursor cursor = getContentResolver()
.query(contactUri, projection, null, null, null);
}
};
Thread queryThread = new Thread(r);
queryThread.start();
cursor.moveToFirst();
int column = cursor.getColumnIndex(ContactsContract.CommonDataKinds.Phone.NUMBER);
所以在这段代码中Android Studio无法解析符号“cursor”:( 到目前为止,我找不到我理解如何使用CursorLoaders进行此操作的指南。
答案 0 :(得分:3)
您可以使用AsyncTask作业!
class WorkCursor extends AsyncTask<Cursor,Object,String> {
String[] projection;
Uri contactUri;
public WorkCursor(String[] projection,Uri contactUri){
this.contactUri = contactUri;
this.projection = projection;
}
@Override
protected String doInBackground(Cursor... cursors) {
//This is done in the background
Cursor cursor = MyActivity.this.getContentResolver()
.query(contactUri, projection, null, null, null);
int column = cursor.getColumnIndex(ContactsContract.CommonDataKinds.Phone.NUMBER);
String number = cursor.getString(column);
return number;
}
@Override
protected void onPostExecute(String number) {
super.onPostExecute(number);
//This is done on the UI thread
functionCall(number);
}
}
public void functionCall(String number){
//This is the UI thread
//You can do whatever you with your number
Toast.makeText(this,"This is the number: "+number,Toast.LENGTH_SHORT).show();
}
然后像这样调用Asynctask:
new WorkCursor(projection,contactUri).execute();
另一种方法是像你一样做但是在线程中完成所有工作然后在UI线程上运行结果,如下所示:
new Thread(new Runnable() {
@Override
public void run() {
Cursor cursor = getContentResolver()
.query(contactUri, projection, null, null, null);
cursor.moveToFirst();
int column = cursor.getColumnIndex(ContactsContract.CommonDataKinds.Phone.NUMBER);
final String number = cursor.getString(column);
runOnUiThread(new Runnable() {
@Override
public void run() {
functionCall(number);
}
});
}
}).run();
字符串编号必须是最终的才能在另一个(在UI上运行)线程中访问!
免责声明:代码未经测试。
答案 1 :(得分:0)
您似乎无法理解启动单独线程意味着什么。光标不仅在示例中超出范围,而且还异步初始化,这意味着在您调用start()
后它不会立即可用。 start()
总是立即完成,只是导致线程在一段时间后执行,而不会阻塞主线程。
在android中,对于大多数用例来说,使用AsyncTask最方便,而不是手动创建单独的线程。有关详细信息,请参阅Processes and Threads guide。