Question

我试图构建一个简单的应用程序，通过以下代码从URL获取Image，但找不到findViewById(FloatingActionButton)错误找到合适的方法，帮助将不胜感激。大多数代码都是android studio的基本版activity的生物传感器，但无论如何都找不到故障代码。

    import android.graphics.Bitmap;
    import android.graphics.BitmapFactory;
    import android.os.AsyncTask;
    import android.os.Bundle;
    import android.support.design.widget.FloatingActionButton;
    import android.support.design.widget.Snackbar;
    import android.support.v7.app.AppCompatActivity;
    import android.support.v7.widget.Toolbar;
    import android.view.Menu;
    import android.view.MenuItem;
    import android.view.View;
    import android.widget.ImageView;
    import java.io.IOException;
    import java.io.InputStream;
    import java.net.HttpURLConnection;
    import java.net.MalformedURLException;
    import java.net.URL;

    import static singh.rahul.com.imagedownloader.R.id.fab;

    public class MainActivity extends AppCompatActivity {

    ImageView imgDownloaded;

    public void DownloadImage(View v){
        ImageDownloaderClass task=new ImageDownloaderClass();
        Bitmap myRawImage;
        try{
            myRawImage=task.execute("Any Image URL").get();
            imgDownloaded.setImageBitmap(myRawImage);
        }catch(Exception e){
            e.printStackTrace();
        }

    }

    public class ImageDownloaderClass extends AsyncTask<String,Void,Bitmap>{
        @Override
        protected Bitmap doInBackground(String... urls){
            try{
                URL url=new URL(urls[0]);
                HttpURLConnection connections=(HttpURLConnection) url.openConnection();
                connections.connect();
                InputStream is=connections.getInputStream();
                Bitmap theBitmap= BitmapFactory.decodeStream(is);
                return theBitmap;

            }catch (MalformedURLException mue){
                mue.printStackTrace();
            }catch(IOException ioe){
                ioe.printStackTrace();
            }

            return null;
        }
    }

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        Toolbar toolbar = (Toolbar) findViewById(R.id.toolbar);
        setSupportActionBar(toolbar);
        imgDownloaded=(ImageView) findViewById(R.id.imageView);
        FloatingActionButton fab = (FloatingActionButton) findViewById(fab);
        fab.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View view) {
                Snackbar.make(view, "Downloading Image...", Snackbar.LENGTH_LONG)
                        .setAction("Action", null).show();
                DownloadImage(View);
            }
        });
    }

    @Override
    public boolean onCreateOptionsMenu(Menu menu) {
        // Inflate the menu; this adds items to the action bar if it is present.
        getMenuInflater().inflate(R.menu.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();

        //noinspection SimplifiableIfStatement
        if (id == R.id.action_settings) {
            return true;
        }

        return super.onOptionsItemSelected(item);
    }
}

期待您的帮助！

Answer 1

而不是fab

FloatingActionButton fab = (FloatingActionButton) findViewById(fab);

您需要传递id（来自xml布局）：

FloatingActionButton fab = (FloatingActionButton) findViewById(R.id.your_fab);

另外，在fab按钮监听器中，这一行：

DownloadImage(View);

应该是：

DownloadImage(view); //lower case

Answer 2

findViewById（int id）

此方法将参数作为int（视图的id）。

FloatingActionButton fab = (FloatingActionButton) findViewById(R.id.yourId);

Answer 3

使用此

FloatingActionButton fab = (FloatingActionButton) findViewById(R.id.fab);

而不是这个

FloatingActionButton fab = (FloatingActionButton) findViewById(fab);

希望这会有所帮助。

找不到适合findViewById的方法（FloatingActionButton）

3 个答案: