[英]How to call a function from a class other than MainActivity on button click in Android Java
[英]Call intent from class other than MainActivity
首先讓我指出,這是我第一次編寫應用程序,甚至是Java。 我習慣於對PHP和JS進行編碼,所以請客氣
我遵循Google指南http://developer.android.com/training/basics/network-ops/connecting.html
這是我的主要活動
package com.example.eerstetest;
import android.app.Activity;
import android.content.Context;
import android.content.Intent;
import android.net.ConnectivityManager;
import android.net.NetworkInfo;
import android.os.Bundle;
import android.view.Menu;
import android.view.View;
import android.widget.EditText;
public class MainActivity extends Activity {
public final static String EXTRA_MESSAGE = "com.example.eerstetest.MESSAGE";
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
}
@Override
public boolean onCreateOptionsMenu(Menu menu) {
// Inflate the menu; this adds items to the action bar if it is present.
getMenuInflater().inflate(R.menu.main, menu);
return true;
}
public void sendMessage(View view) {
Intent intent = new Intent(this, DisplayMessageActivity.class);
EditText editText = (EditText) findViewById(R.id.edit_message);
String message = editText.getText().toString();
intent.putExtra(EXTRA_MESSAGE, message);
startActivity(intent);
}
public void getUpdate(View view) {
Intent intent = new Intent(this, DisplayMessageActivity.class);
// see if there is a data connection
ConnectivityManager connMgr = (ConnectivityManager) getSystemService(Context.CONNECTIVITY_SERVICE);
NetworkInfo networkInfo = connMgr.getActiveNetworkInfo();
if (networkInfo != null && networkInfo.isConnected()) {
// fetch data
//textView.setText("Network connection available.");
String dataUrl = "http://www.myurl.com";
new DownloadUpdate().execute(dataUrl);
} else {
// display error
//textView.setText("No network connection available.");
String message = "No network connection available.";
intent.putExtra(EXTRA_MESSAGE, message);
startActivity(intent);
}
}
}
如您所見,我有一個可以使用DisplayMessageActivity的sendMessage方法,還有一個getUpdate方法,可以調用單獨的.java文件中的DownloadUpdate類。
package com.example.eerstetest;
import java.io.IOException;
import java.io.InputStream;
import java.io.InputStreamReader;
import java.io.Reader;
import java.io.UnsupportedEncodingException;
import java.net.HttpURLConnection;
import java.net.URL;
import android.content.Context;
import android.content.Intent;
import android.os.AsyncTask;
import android.util.Log;
// Uses AsyncTask to create a task away from the main UI thread. This task takes a
// URL string and uses it to create an HttpUrlConnection. Once the connection
// has been established, the AsyncTask downloads the contents of the webpage as
// an InputStream. Finally, the InputStream is converted into a string, which is
// displayed in the UI by the AsyncTask's onPostExecute method.
public class DownloadUpdate extends AsyncTask<String, Integer, String> {
private static final String DEBUG_TAG = "HttpExample";
//private TextView textView;
public final static String EXTRA_MESSAGE = "com.example.eerstetest.MESSAGE";
@Override
protected String doInBackground(String... url) {
// params comes from the execute() call: params[0] is the url.
try {
return downloadUrl(url[0]);
} catch (IOException e) {
return "Unable to retrieve web page. URL may be invalid.";
}
}
// onPostExecute displays the results of the AsyncTask.
@Override
protected void onPostExecute(String result) {
//textView.setText(result);
Intent intent = new Intent(this, DisplayMessageActivity.class);
intent.putExtra(EXTRA_MESSAGE, result);
startActivity(intent);
}
// Given a URL, establishes an HttpUrlConnection and retrieves
// the web page content as a InputStream, which it returns as
// a string.
private String downloadUrl(String myurl) throws IOException {
InputStream is = null;
// Only display the first 500 characters of the retrieved
// web page content.
int len = 500;
try {
URL url = new URL(myurl);
HttpURLConnection conn = (HttpURLConnection) url.openConnection();
conn.setReadTimeout(10000 /* milliseconds */);
conn.setConnectTimeout(15000 /* milliseconds */);
conn.setRequestMethod("GET");
conn.setDoInput(true);
// Starts the query
conn.connect();
int response = conn.getResponseCode();
Log.d(DEBUG_TAG, "The response is: " + response);
is = conn.getInputStream();
// Convert the InputStream into a string
String contentAsString = readIt(is, len);
return contentAsString;
// Makes sure that the InputStream is closed after the app is
// finished using it.
} finally {
if (is != null) {
is.close();
}
}
}
// Reads an InputStream and converts it to a String.
public String readIt(InputStream stream, int len) throws IOException, UnsupportedEncodingException {
Reader reader = null;
reader = new InputStreamReader(stream, "UTF-8");
char[] buffer = new char[len];
reader.read(buffer);
return new String(buffer);
}
}
我不明白從此處調用DisplayMessageActivity時必須為上下文填寫什么
為了完整起見,這是清單文件
<?xml version="1.0" encoding="utf-8"?>
<manifest xmlns:android="http://schemas.android.com/apk/res/android"
package="com.example.eerstetest"
android:versionCode="1"
android:versionName="1.0" >
<uses-sdk
android:minSdkVersion="8"
android:targetSdkVersion="17" />
<uses-permission android:name="android.permission.INTERNET" />
<uses-permission android:name="android.permission.ACCESS_NETWORK_STATE" />
<application
android:allowBackup="true"
android:icon="@drawable/ic_launcher"
android:label="@string/app_name"
android:theme="@style/AppTheme" >
<activity
android:name="com.example.eerstetest.MainActivity"
android:label="@string/app_name" >
<intent-filter>
<action android:name="android.intent.action.MAIN" />
<category android:name="android.intent.category.LAUNCHER" />
</intent-filter>
</activity>
<activity
android:name="com.example.eerstetest.DisplayMessageActivity"
android:label="@string/title_activity_display_message"
android:parentActivityName="com.example.eerstetest.MainActivity" >
<meta-data
android:name="android.support.PARENT_ACTIVITY"
android:value="com.example.eerstetest.MainActivity" />
</activity>
<activity
android:name="com.example.eerstetest.DownloadUpdate"
android:label="@string/title_activity_download_update" >
</activity>
</application>
</manifest>
如果我可以提供其他任何服務,請告訴我
像這樣傳遞上下文作為參數:
new DownloadUpdate(MainActivity.this).execute(dataUrl);
在DownloadUpdate中添加構造函數:
Context context;
public DownloadUpdate(Context context){
this.context = context
}
然后使用DownloadUpdate類中的上下文作為全局參數,並使用此方法調用意圖
Intent intent = new Intent(DownloadUpdate.this, DisplayMessageActivity.class);
intent.putExtra(EXTRA_MESSAGE, result);
context.startActivity(intent);
像這樣打電話:
Intent intent = new Intent(DownloadUpdate.this, DisplayMessageActivity.class);
intent.putExtra(EXTRA_MESSAGE, result);
startActivity(intent);
我認為您從另一個類或活動中調用DownloadUpdate
為:
new DownloadUpdate().execute(params);
要解決DownloadUpdate
的上下文問題,請創建類似以下的構造函數:
public DownloadUpdate(Context context){
this.context = context;
}
這里this.context
表示您在DownloadUpdate
類中全局聲明的Context
變量。 然后以以下方式調用DownloadUpdate
:
new DownloadUpdate(your_context).execute(params);
然后使用您在DownloadUpdate
獲得的上下文來創建您的意圖。 喜歡:
@Override
protected void onPostExecute(String result) {
//textView.setText(result);
Intent intent = new Intent(context, DisplayMessageActivity.class);
intent.putExtra(EXTRA_MESSAGE, result);
startActivity(intent);
}
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