安卓开发日记---2017.10.23

继续积累吧。

Intent

这周我主要学习了Android中的Intent模块，做了一些小的练习，熟悉了这个模块的使用方法。从直观上理解，Intent可以看作一种消息机制，从一个Activity到另一个Activity，或者从一个app到另一个app。

创建一个新的Activity

在Android中，我们需要从一个Activity中，创建另一个Activity，来实现UI的切换。实现之一目标的方法是startActivity方法。在startActivity方法中，我们需要一个Intent类型的参数，这个参数可以携带一些key-value数据，并将其传入到新创建的Activity中。

                String textEntered = mNameEntry.getText().toString();                /*                 * Storing the Context in a variable in this case is redundant since we could have                 * just used "this" or "MainActivity.this" in the method call below. However, we                 * wanted to demonstrate what parameter we were using "MainActivity.this" for as                 * clear as possible.                 */                Context context = MainActivity.this;                /* This is the class that we want to start (and open) when the button is clicked. */                Class destinationActivity = ChildActivity.class;                /*                 * Here, we create the Intent that will start the Activity we specified above in                 * the destinationActivity variable. The constructor for an Intent also requires a                 * context, which we stored in the variable named "context".                 */                Intent startChildActivityIntent = new Intent(context, destinationActivity);                // COMPLETED (2) Use the putExtra method to put the String from the EditText in the Intent                /*                 * We use the putExtra method of the Intent class to pass some extra stuff to the                 * Activity that we are starting. Generally, this data is quite simple, such as                 * a String or a number. However, there are ways to pass more complex objects.                 */                startChildActivityIntent.putExtra(Intent.EXTRA_TEXT, textEntered);                /*                 * Once the Intent has been created, we can use Activity's method, "startActivity"                 * to start the ChildActivity.                 */                startActivity(startChildActivityIntent);

隐式Intent

隐式Intent的主要目的是使用Android系统中其他App提供的公共服务，例如：浏览器，地图等工具。这些隐式Intent的信息可以在Android的官方开发文档中找到。

打开一个网页

    private void openWebPage(String url) {        /*         * We wanted to demonstrate the Uri.parse method because its usage occurs frequently. You         * could have just as easily passed in a Uri as the parameter of this method.         */        Uri webpage = Uri.parse(url);        /*         * Here, we create the Intent with the action of ACTION_VIEW. This action allows the user         * to view particular content. In this case, our webpage URL.         */        Intent intent = new Intent(Intent.ACTION_VIEW, webpage);        /*         * This is a check we perform with every implicit Intent that we launch. In some cases,         * the device where this code is running might not have an Activity to perform the action         * with the data we've specified. Without this check, in those cases your app would crash.         */        if (intent.resolveActivity(getPackageManager()) != null) {            startActivity(intent);        }    }

打开地图，并进行定位

    public void onClickOpenAddressButton(View v) {        String addressString = "1600 Amphitheatre Parkway, CA";        Uri.Builder builder = new Uri.Builder();        builder.scheme("geo")                .path("0,0")                .query(addressString);        Uri addressUri = builder.build();        showMap(addressUri);    }    private void showMap(Uri geoLocation) {        /*         * Again, we create an Intent with the action, ACTION_VIEW because we want to VIEW the         * contents of this Uri.         */        Intent intent = new Intent(Intent.ACTION_VIEW);        /*         * Using setData to set the Uri of this Intent has the exact same affect as passing it in         * the Intent's constructor. This is simply an alternate way of doing this.         */        intent.setData(geoLocation);        if (intent.resolveActivity(getPackageManager()) != null) {            startActivity(intent);        }    }

共享消息

在Android中，我们会将一些内容进行共享，例如：文本，音频，视频等。这时候我们需要ShareCompat创建一个共享的Intent，并提供给可以处理的App。例如：将文本信息交给剪贴板。

    void shareTest(String textToShare){        String mineType = "text/plain";        String title = "Learning how to share";        ShareCompat.IntentBuilder.from(this)                .setType(mineType)                .setChooserTitle(title)                .setText(textToShare)                .startChooser();    }

在这里，如果我们将一个Intent绑定到一个MenuItem中，可以使用setIntent方法。在点击这个MenuItem之后，就会自动使用这个共享Intent分享到其他的应用中。

    private Intent createShareForecastIntent() {        Intent shareIntent = ShareCompat.IntentBuilder.from(this)                .setType("text/plain")                .setText(mForecast + FORECAST_SHARE_HASHTAG)                .getIntent();        return shareIntent;    }    @Override    public boolean onCreateOptionsMenu(Menu menu) {        getMenuInflater().inflate(R.menu.detail, menu);        MenuItem menuItem = menu.findItem(R.id.action_share);        menuItem.setIntent(createShareForecastIntent());        return true;    }