Question

activity_main.xml的代码：

<ScrollView
    xmlns:android="http://schemas.android.com/apk/res/android"
    android:layout_height="match_parent"
    android:layout_width="match_parent">
    <LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
            xmlns:tools="http://schemas.android.com/tools"
            android:layout_width="match_parent"
            android:layout_height="match_parent"
            android:paddingBottom="@dimen/activity_vertical_margin"
            android:paddingLeft="@dimen/activity_horizontal_margin"
            android:paddingRight="@dimen/activity_horizontal_margin"
            android:paddingTop="@dimen/activity_vertical_margin"
            tools:context="com.example.android.httptry.MainActivity"
            android:orientation="vertical">


            <EditText
                android:id="@+id/myUrl"
                android:layout_width="match_parent"
                android:layout_height="wrap_content"
                android:hint="@string/hint"/>

            <Button
                android:layout_width="wrap_content"
                android:layout_height="wrap_content"
                android:id="@+id/button"
                android:text="@string/button"
                android:layout_gravity="center_horizontal"
                android:layout_marginTop="20dp"
                android:layout_marginBottom="20dp"
                android:onClick="myClickHandler"
                />

            <TextView
                android:id="@+id/myText"
                android:layout_width="wrap_content"
                android:layout_height="wrap_content"
                />
    </LinearLayout>
</ScrollView>

HttpExampleActivity.java的代码：

public class HttpExampleActivity extends Activity {
private static final String DEBUG_TAG = "HttpExample";
private EditText urlText;
private TextView textView;

@Override
public void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_main);
    urlText = (EditText) findViewById(R.id.myUrl);
    textView = (TextView) findViewById(R.id.myText);
}

// When user clicks button, calls AsyncTask.

public void myClickHandler(View view) {
    // Gets the URL from the UI's text field.
    String stringUrl = urlText.getText().toString();
    ConnectivityManager connMgr = (ConnectivityManager)
            getSystemService(Context.CONNECTIVITY_SERVICE);
    NetworkInfo networkInfo = connMgr.getActiveNetworkInfo();
    if (networkInfo != null && networkInfo.isConnected()) {
        new DownloadWebpageTask().execute(stringUrl);
    } else {
        textView.setText("No network connection available.");
    }
}

private class DownloadWebpageTask extends AsyncTask<String, Void, String> {
    @Override
    protected String doInBackground(String... urls) {

        // params comes from the execute() call: params[0] is the url.
        try {
            return downloadUrl(urls[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);
    }
}

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);
}

}

在检查logcat时，我发现了以下错误消息：

Process: com.example.android.httptry, PID: 29936


java.lang.IllegalStateException: Could not find method myClickHandler(View) in a parent or ancestor Context for android:onClick attribute defined on view class android.support.v7.widget.AppCompatButton with id 'button'

我对Android开发相当新，所以无法理解为什么尽管命名onClick（）方法我得到了上述错误。解决这个问题的任何解决方案？

Answer 1

我知道这很傻，但它发生在我身上，我错过了 android：clickable =＆＃34; true＆＃34;

Answer 2

更改

tools:context="com.example.android.httptry.MainActivity"

到

tools:context="com.yourpackage.HttpExampleActivity"

或在myClickHandler课程中定义com.example.android.httptry.MainActivity方法（如果有任何此类课程）

您共享的堆栈跟踪清楚地表明了这一点它正在寻找在给定的上下文中定义的myClickHandler(View)方法，在这种情况下是com.example.android.httptry.MainActivity，但在该活动中没有定义这样的方法。

它在HttpExampleActivity。

因此，无论是更改上下文还是在上下文类中定义此类方法，都可以清楚地表明这一点。

按钮onClick（）不加载自定义类HttpExampleActivity.java中定义的myClickHandler方法

2 个答案: