Getting started with the Android messaging mechanism

Then deal with the problems that appear in the Android Network picture Viewer

To modify the original program using the Add child thread:

 PackageCom.wuyudong.imagesviewer;ImportJava.io.InputStream;Importjava.net.HttpURLConnection;Importjava.net.MalformedURLException;ImportJava.net.URL;Importorg.apache.http.HttpConnection;ImportAndroid.os.Bundle;Importandroid.app.Activity;ImportAndroid.graphics.Bitmap;Importandroid.graphics.BitmapFactory;Importandroid.text.TextUtils;ImportAndroid.view.Menu;ImportAndroid.view.View;ImportAndroid.widget.EditText;ImportAndroid.widget.ImageView;ImportAndroid.widget.Toast; Public classMainactivityextendsActivity {PrivateEditText Et_path; PrivateImageView IV; @Overrideprotected voidonCreate (Bundle savedinstancestate) {Super. OnCreate (savedinstancestate);        Setcontentview (R.layout.activity_main); Et_path=(EditText) Findviewbyid (R.id.et_path); IV=(ImageView) Findviewbyid (R.ID.IV); }     Public voidClick (View view) {FinalString Path =Et_path.gettext (). toString (). Trim (); if(Textutils.isempty (path)) {Toast.maketext ( This, "Picture path cannot be empty", 0). Show (); } Else {             New  Thread () {@Override   public void  run () { //Connect server GET request get picture                    Try{URL URL=NewURL (path); //request to send HTTP from URLHttpURLConnection conn =(httpurlconnection) URL. OpenConnection (); //How to set the requestConn.setrequestmethod ("GET"); Conn.setconnecttimeout (5000); Conn.setreadtimeout (5000); Conn.setrequestproperty ("User-agent",                                "mozilla/5.0 (Windows NT 6.1; WOW64) applewebkit/537.36 (khtml, like Gecko) chrome/45.0.2454.101 safari/537.36 "); intCode =Conn.getresponsecode (); if(Code = = 200) {InputStream is=Conn.getinputstream (); Bitmap Bitmap=Bitmapfactory.decodestream (IS);                        Iv.setimagebitmap (bitmap); } Else{toast.maketext (mainactivity). This, "Show Picture Failed", 0). Show (); }                    } Catch(Exception e) {//TODO auto-generated Catch blockE.printstacktrace (); Toast.maketext (mainactivity. This, "Access failed to get picture", 0). Show ();        }}}.start (); }    }}

Error after running the project:

06-27 19:27:59.613:w/system.err (2471): Android.view.viewrootimpl$calledfromwrongthreadexception:only the original Thread that created a view hierarchy can touch it views.

Who created the View object, who can move the view.

Code: Iv.setimagebitmap (bitmap), the goal is to modify the UI

It is the main thread that can be modified. To control multi-threaded changes to the view synchronization problem set

The modified code is as follows:

 PackageCom.wuyudong.imagesviewer;ImportJava.io.InputStream;Importjava.net.HttpURLConnection;Importjava.net.MalformedURLException;ImportJava.net.URL;Importorg.apache.http.HttpConnection;ImportAndroid.os.Bundle;ImportAndroid.os.Handler;ImportAndroid.os.Message;Importandroid.app.Activity;ImportAndroid.graphics.Bitmap;Importandroid.graphics.BitmapFactory;Importandroid.text.TextUtils;ImportAndroid.view.Menu;ImportAndroid.view.View;ImportAndroid.widget.EditText;ImportAndroid.widget.ImageView;ImportAndroid.widget.Toast; Public classMainactivityextendsActivity {protected Static Final intCHANGE_UI = 1; protected Static Final intERROR = 2; PrivateEditText Et_path; PrivateImageView IV; //1, the main thread to create the message processor Private Handler Handler = new  Handler () {   public void  Handleme Ssage (Android.os.Message msg) {  if (msg.what = = change_ui) {Bitmap Bitmap 
     = (Bitmap) msg.obj;            Iv.setimagebitmap (bitmap); }  Else if (msg.what = = ERROR) {toast.maketext (mainactivity. This, "Access failed to get Picture", 0      ). Show ();    }        };    }; @Overrideprotected voidonCreate (Bundle savedinstancestate) {Super. OnCreate (savedinstancestate);        Setcontentview (R.layout.activity_main); Et_path=(EditText) Findviewbyid (R.id.et_path); IV=(ImageView) Findviewbyid (R.ID.IV); }     Public voidClick (View view) {FinalString Path =Et_path.gettext (). toString (). Trim (); if(Textutils.isempty (path)) {Toast.maketext ( This, "Picture path cannot be empty", 0). Show (); } Else {            NewThread () {@Override Public voidrun () {//Connect server GET request get picture                    Try{URL URL=NewURL (path); //request to send HTTP from URLHttpURLConnection conn =(httpurlconnection) URL. OpenConnection (); //How to set the requestConn.setrequestmethod ("GET"); Conn.setconnecttimeout (5000); Conn.setreadtimeout (5000); Conn.setrequestproperty ("User-agent",                                "mozilla/5.0 (Windows NT 6.1; WOW64) applewebkit/537.36 (khtml, like Gecko) chrome/45.0.2454.101 safari/537.36 "); //get the response code returned by the server                        intCode =Conn.getresponsecode (); if(Code = = 200) {InputStream is=Conn.getinputstream (); Bitmap Bitmap=Bitmapfactory.decodestream (IS); //Iv.setimagebitmap (bitmap); //TODO: Tell the main thread a message: Help me change the interface, content: Bitmap                       message msg = new  message ();                            Msg.what = change_ui; Msg.obj = bitmap;                        Handler.sendmessage (msg); } Else {                            //Toast.maketext (Mainactivity.this, "show Picture Failed", 0)//. Show ();                        message msg = new  message (); Msg.what = ERROR;                        Handler.sendmessage (msg); }                    } Catch(Exception e) {//TODO auto-generated Catch blockE.printstacktrace (); //Toast.maketext (mainactivity.this, "Access failed to get Picture",//0). Show ();                     message msg = new  message (); Msg.what = ERROR;                    Handler.sendmessage (msg);        }}}.start (); }    }}

Getting started with the Android messaging mechanism