为什么setOnLongClickListener for TouchImageView不起作用？

Question

帮帮我，为什么“ img.setOnLongClickListener”在此代码中不起作用？ 我在屏幕上拨动很长，但是没有显示出alertdialog。

打包com.me.life;

    import android.app.AlertDialog;
    import android.content.DialogInterface;
    import android.graphics.Bitmap;
    import android.graphics.BitmapFactory;
    import android.os.Bundle;
    import android.os.Environment;
    import android.support.annotation.Nullable;
    import android.support.v7.app.AppCompatActivity;
    import android.view.View;
    import android.widget.EditText;
    import android.widget.Toast;
    import java.io.File;

公共类Show_big_image扩展了AppCompatActivity {     私有字符串表，文件夹= Environment.getExternalStorageDirectory（）+“ /life/.images”;     私有String []轴名；     选择了私有int;     私有位图myBitmap;     Database_class db;

@Override
protected void onCreate(@Nullable Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.show_big_image);
    db = new Database_class(this);
}

@Override
protected void onResume() {
    super.onResume();
    selected=getIntent().getIntExtra("selectedpic", 0);
    axname = getIntent().getStringArrayExtra("allpicname");
    table= getIntent().getExtras().getString("table");
    show_pic();

}

public void show_pic ()
{
    try {
        db.open();
        final String toz=db.get_image_tozih(axname[selected] ,table);
        db.close();
        File imgFile = new File(folder +"/"+axname[selected]+".png");
        myBitmap = BitmapFactory.decodeFile(imgFile.getAbsolutePath());
        TouchImageView img = new TouchImageView(this);
        img.setImageBitmap(myBitmap);
        img.setMaxZoom(4f);
        setContentView(img);
        img.setOnLongClickListener(new View.OnLongClickListener() {
            @Override
            public boolean onLongClick(View view) {

                AlertDialog.Builder alert = new AlertDialog.Builder(Show_big_image.this);
                final EditText edittext = new EditText(Show_big_image.this);
                edittext.setText(toz);
                alert.setView(edittext);
                alert.setPositiveButton("ok", new DialogInterface.OnClickListener() {
                    public void onClick(DialogInterface dialog, int whichButton) {
                        db.open();
                        db.edit_image_tozih(edittext.getText().toString(), axname[selected] ,table);
                        db.close();
                        show_pic();
                    }
                });
                alert.show();

                return false;
            }
        });
        img.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View view) {
                AlertDialog.Builder alert = new AlertDialog.Builder(Show_big_image.this);
                alert.setPositiveButton("next", new DialogInterface.OnClickListener() {
                    public void onClick(DialogInterface dialog, int whichButton) {
                        if((axname.length-selected)>=2){
                            myBitmap.recycle();
                            selected=selected+1;
                            show_pic();
                        }
                    }
                });
                alert.setNegativeButton("back", new DialogInterface.OnClickListener() {
                    public void onClick(DialogInterface dialog, int whichButton) {
                        if(selected!=0) {
                            myBitmap.recycle();
                            selected = selected - 1;
                            show_pic();
                        }
                    }
                });
                alert.show();
            }
        });

    } catch (Exception e) {
        Toast.makeText(getApplicationContext(),"error",Toast.LENGTH_SHORT).show();
    }
}

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

@Override
public void onBackPressed() {
    super.onBackPressed();
    myBitmap.recycle();
    finish();
}

}