手机截屏并用Dialog展示

public class MainActivity extends AppCompatActivity {
ImageView image;
Button button;
Bitmap bitmap;
Dialog dia;
Context context;
ImageView imageView;
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
context=this;
image = (ImageView) findViewById(R.id.image);
button = (Button) findViewById(R.id.button);

button.setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View v) {
//截屏
View view = getWindow().getDecorView();
view.setDrawingCacheEnabled(true);
view.buildDrawingCache();
bitmap = view.getDrawingCache();
//截屏后用Dialog展示
showDialog(bitmap);

}
});
}

public void showDialog(Bitmap bitmap){
dia = new Dialog(context, R.style.edit_AlertDialog_style);
dia.setContentView(R.layout.activity_start_dialog);
imageView=(ImageView) dia.findViewById(R.id.im);
imageView.setImageBitmap(bitmap);
dia.show();
}
}