java - onClick 方法不存在

Question

(!)onClick 方法不存在

Corresponding method handler 'public void navigate(android.view.View)' not found The onClick attribute value should be the name of a method in this View's context to invoke when the view is clicked. This name must correspond to a public method that takes exactly one parameter of type View. Must be a string value, using '\;' to escape characters such as '\n' or '\uxxxx' for a unicode character.

* 您好，我是新来的，我只是在 Coursera 上尝试类(class)，但它似乎已经过时了，而且有些东西没有按预期正常工作。 我一直试图在论坛上搜索以找到答案，并且尝试了一些方法，但似乎我太弱智了，而且还是个新手。 这可能与我的工具:上下文有关吗？

这是我的 xml:

<RelativeLayout
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:padding="16dp"
tools:context="MainActivity"
android:background="#ffffff">


<NumberPicker
    android:id="@+id/numberPicker"
    android:layout_width="wrap_content"
    android:layout_height="wrap_content"
    android:layout_alignParentTop="true"
    android:layout_alignParentLeft="true"
    android:layout_alignParentStart="true"
    />

<Button
    android:layout_width="wrap_content"
    android:layout_height="wrap_content"
    android:text="OK"
    android:id="@+id/button"
    android:layout_below="@+id/numberPicker"
    android:layout_alignParentLeft="true"
    android:layout_alignParentStart="true"
    android:onClick="navigate"/>

<WebView
    android:layout_width="wrap_content"
    android:layout_height="wrap_content"
    android:id="@+id/webView"
    android:layout_below="@+id/button"
    android:layout_alignParentLeft="true"
    android:layout_alignParentStart="true" />

这是我的java:

import android.support.v7.app.AppCompatActivity;
import android.os.Bundle;
import android.webkit.WebView;
import android.webkit.WebViewClient;
import android.widget.NumberPicker;
import android.view.View;

public class MainActivity extends AppCompatActivity {

NumberPicker possibilities;
WebView webView;


@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_main);

    possibilities = (NumberPicker) findViewById(R.id.numberPicker);
    webView = (WebView) findViewById(R.id.webView);
    String[] possibilitiesStrings = {
            "Android",
            "Checklist text-input fields",
            "Coursera",
            "Supelec",
    };
    possibilities.setDisplayedValues(possibilitiesStrings);
    possibilities.setMinValue(0);
    possibilities.setMaxValue(possibilitiesStrings.length - 1);

    /**
     * called when the OK button from activity_main.xml is clicked
     * @param v the View which triggered the method call: the OK button
     */
    public void navigate(View v) {
    int choice = possibilities.getValue();
        webView.setWebViewClient(new WebViewClient());
    if (choice == 0)
        webView.loadUrl("file:///android_asset/android.html");
    else if (choice == 1)
    webView.loadUrl("file:///android_asset/checklist.html");
else if (choice == 2)
    webView.loadUrl("http:///www.coursera.org");
else if (choice == 3)
    webView.loadUrl("file:///android_asset/supelec.html");
}

}


}
}

Answer 1

我分析了您的代码，发现您在 onCreate() 方法中声明了您的导航方法，因此您可以从 xml 中找到它。

如何在 xml 中声明方法的示例

import android.support.v7.app.AppCompatActivity;
import android.os.Bundle;
import android.webkit.WebView;
import android.webkit.WebViewClient;
import android.widget.NumberPicker;
import android.view.View;

public class MainActivity extends AppCompatActivity {

    NumberPicker possibilities;
    WebView webView;


    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);

        possibilities = (NumberPicker) findViewById(R.id.numberPicker);
        webView = (WebView) findViewById(R.id.webView);
        String[] possibilitiesStrings = {
                "Android",
                "Checklist text-input fields",
                "Coursera",
                "Supelec",
        };
        possibilities.setDisplayedValues(possibilitiesStrings);
        possibilities.setMinValue(0);
        possibilities.setMaxValue(possibilitiesStrings.length - 1);

    }

    /**
     * called when the OK button from activity_main.xml is clicked
     * @param v the View which triggered the method call: the OK button
     */
    public void navigate(View v) {
        int choice = possibilities.getValue();
        webView.setWebViewClient(new WebViewClient());
        if (choice == 0)
            webView.loadUrl("file:///android_asset/android.html");
        else if (choice == 1)
            webView.loadUrl("file:///android_asset/checklist.html");
        else if (choice == 2)
            webView.loadUrl("http:///www.coursera.org");
        else if (choice == 3)
            webView.loadUrl("file:///android_asset/supelec.html");
    }
}