Android 在一个应用中怎么启动另外一个已安装的应用

在自己的apk中如何来启动另外的一个apk

package com.cn;import android.app.Activity;import android.content.ComponentName;import android.content.Intent;import android.os.Bundle;import android.view.View;import android.widget.Button;public class MainActivity extends Activity {	private Button myBut;	private String tongfang = "com.android.tongfang";	@Override	public void onCreate(Bundle savedInstanceState) {		super.onCreate(savedInstanceState);		setContentView(R.layout.main);		myBut = (Button) findViewById(R.id.my_but);		myBut.setOnClickListener(new Button.OnClickListener() {			public void onClick(View v) {				//Intent intent = new Intent(tongfang);				//startActivity(intent);			Intent mIntent = new Intent( ); 				ComponentName comp = new ComponentName(tongfang, "com.android.tongfang.MainActivity");     				mIntent.setComponent(comp); 				mIntent.setAction("android.intent.action.VIEW"); 				startActivity(mIntent);			}		});	}}

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