Question

这是我的Activity类中的代码部分。这是onListItemClick方法。我使用String数组输入菜单活动类名。 classes是数组。

protected void onListItemClick(ListView l, View v, int position, long id) {
        super.onListItemClick(l, v, position, id);
        String cheese = classes[position];
        try {
            Class ourClass = Class.forName("com.example.image_and_sound_app."+cheese);
            Intent ourIntent = new Intent(Menu.this,ourClass);
            startActivity(ourIntent);
        } catch (ClassNotFoundException e) {
            e.printStackTrace();
        }

    }

但是当我点击一个列表项时，会发生这样的异常

nd_sound_app.app W/System.err﹕ Caused by: java.lang.ClassNotFoundException: Didn't find class "com.example.image_and_sound_app.MainActivity" on path: DexPathList[[zip file "/data/app/com.example.image_and_sound_app.app-2.apk"],nativeLibraryDirectories=[/data/app-lib/com.example.image_and_sound_app.app-2, /system/lib]]
07-09 15:50:14.220    1288-1288/com.example.image_and_sound_app.app W/System.err﹕ at dalvik.system.BaseDexClassLoader.findClass(BaseDexClassLoader.java:56)
07-09 15:50:14.220    1288-1288/com.example.image_and_sound_app.app W/System.err﹕ at java.lang.ClassLoader.loadClass(ClassLoader.java:497)
07-09 15:50:14.220    1288-1288/com.example.image_and_sound_app.app W/System.err﹕ at java.lang.ClassLoader.loadClass(ClassLoader.java:457)

已经存在MainActivity类。但是例外表明找不到类。我该如何解决这个问题？

Answer 1

所以你给错了类名。 MainActivity类名称不是：com.example.image_and_sound_app.MainActivity。仔细检查主要活动的所有包名称。不能做任何其他事情。

Answer 2

很抱歉，如果我不使用评论选项，我的代表太低了。我知道如何帮助你......

我看到你在buckysroom上做了Android教程。

您在上述评论中所写的内容并非主要活动的声明。您只需将链接构建到活动本身。

String classes[] = {"MainActivity", "TextPlay", "Email", "Notebook", "example4", "example5", "example6" };

这一行只是一个后来的代码构建链接的数组。

 Class ourClass = null;
    try {
        ourClass = Class.forName("com.awo.travistut."+links);
        Intent ourIntent = new Intent(Menu.this, ourClass);
        startActivity(ourIntent);
    } catch (ClassNotFoundException e) {
        e.printStackTrace();
    }

这是缺少的主要类：

import android.support.v7.app.ActionBarActivity;
import android.os.Bundle;
import android.view.Menu;
import android.view.MenuItem;
import android.view.SoundEffectConstants;
import android.view.View;
import android.widget.Button;
import android.widget.TextView;


public class MainActivity extends ActionBarActivity {

int counter;
Button add, sub;
TextView display;

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

    counter = 0;
    add = (Button) findViewById(R.id.bAdd);
    sub = (Button) findViewById(R.id.bDelete);
    display = (TextView) findViewById(R.id.tvDisplay);

    add.setOnClickListener(new View.OnClickListener() {
        @Override
        public void onClick(View v) {
            counter = counter+1;
            display.setText("Your total is " + counter);
            v.playSoundEffect(SoundEffectConstants.CLICK);
        }
    });

    sub.setOnClickListener(new View.OnClickListener() {
        @Override
        public void onClick(View v) {
            counter = counter-1;
            display.setText("Your total is " + counter);
            v.playSoundEffect(SoundEffectConstants.CLICK);
        }
    });

}


@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;
}

@Override
public boolean onOptionsItemSelected(MenuItem item) {
    // Handle action bar item clicks here. The action bar will
    // automatically handle clicks on the Home/Up button, so long
    // as you specify a parent activity in AndroidManifest.xml.
    int id = item.getItemId();
    if (id == R.id.action_settings) {
        return true;
    }
    return super.onOptionsItemSelected(item);
}

@Override
protected void onPause(){
    super.onPause();
    finish();
}

}

这是构建导航的菜单代码：

public class Menu extends ListActivity {

String classes[] = {"MainActivity", "TextPlay", "Email", "Notebook", "example4", "example5", "example6" };

@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);

    setListAdapter(new ArrayAdapter<String>(Menu.this, android.R.layout.simple_list_item_1, classes));
}

@Override
protected void onListItemClick(ListView l, View v, int position, long id) {

    super.onListItemClick(l, v, position, id);

    String links = classes[position];

    Class ourClass = null;
    try {
        ourClass = Class.forName("com.awo.travistut."+links);
        Intent ourIntent = new Intent(Menu.this, ourClass);
        startActivity(ourIntent);
    } catch (ClassNotFoundException e) {
        e.printStackTrace();
    }

}

Answer 3

为什么你们将解决方法拉到简单的问题？您可以采用更高效，更可靠的方式，而不是使用反射。这是你的代码：

protected void onListItemClick(ListView l, View v, int position, long id) {
    super.onListItemClick(l, v, position, id);
    String cheese = classes[position];
    try {
        Class ourClass = Class.forName("com.example.image_and_sound_app."+cheese);
        Intent ourIntent = new Intent(Menu.this,ourClass);
        startActivity(ourIntent);
    } catch (ClassNotFoundException e) {
        e.printStackTrace();
    }
}

让我们假设类是：

private static final String[] classes = {
    "A",
    "B",
    "C"
};

等等。不是动态构建类，而是构建它们！

private static final Class<?>[] classes = {
    A.class,
    B.class,
    C.class
};

...

protected void onListItemClick(ListView l, View v, int position, long id) {
    super.onListItemClick(l, v, position, id); // this line is redundant
    Class<?> ourClass = classes[position];
    Intent ourIntent = new Intent(Menu.this,ourClass);
    startActivity(ourIntent);
}

还有一个很好的导航处理模式，但我不知道你是否会使用它。

在android中提供正确的类时会发生class not found异常

3 个答案: